The session welcomes papers on:

1) Forecasting and simulating high impact weather events - research on improvement of high-resolution numerical model prediction of severe weather events (such as winter storms, tropical storms, and severe mesoscale convective storms) using data from various observational platforms, evaluation of the impact of new remote sensing data;

2) Development and improvement of model numerics - basic research on advanced numerical techniques for weather and climate models (such as cloud resolving global model and high-resolution regional models specialized for extreme weather events on sub-synoptic scales);

3) Development and improvement of model physics - progress in research on advanced model physics parametrization schemes (such as stochastic physics, air-wave-oceans coupling physics, turbulent diffusion and interaction with the surface, sub-grid condensation and convection, grid-resolved cloud and precipitation, land-surface parametrization, and radiation);

4) Model evaluation - verification of model components and operational NWP products against theories and observations, regional and global re-analysis of past observations, diagnosis of data assimilation systems;

5) Data assimilation systems - progress in the development of data assimilation systems for operational applications (such as reanalysis and climate services), research on advanced methods for data assimilation on various scales (such as treatment of model and observation errors in data assimilation, and observational network design and experiments);

6) Ensemble forecasts and predictability - strategies in ensemble construction, model resolution and forecast range-related issues, and applications to data assimilation;

7) Advances and challenges in high-resolution simulations and forecasting.

Forecasting the weather, in particular severe and extreme weather has always been the most important subject in meteorology. This session will focus on recent research and developments on forecasting techniques, in particular those designed for operations and impact oriented. Contributions related to nowcasting, meso-scale and convection permitting modelling, ensemble prediction techniques, and statistical post-processing are very welcome.
Topics may include:
- Nowcasting methods and systems, use of observations and weather analysis
- Mesoscale and convection permitting modelling
- Ensemble prediction techniques
- Ensemble-based products for severe/extreme weather forecasting
- Seamless deterministic and probabilistic forecast prediction
- Post-processing techniques, statistical methods in prediction
- Use of machine learning, data mining and other advanced analytical techniques
- Impact oriented weather forecasting
- Presentation of results from relevant international research projects of EU, WMO, and EUMETNET etc.

This session invites contributions that span all aspects of physical processes, prediction methods, predictability, societal impacts and climate services in the 2-weeks-to-2-months lead timescale. We encourage studies on

(a) the Madden Julian Oscillation (MJO) and other modes of variability impacting the S2S timescale,
(b) tropical/extratropical wave dynamics,
(c) teleconnections and cross-timescale interference of climate modes of variability,
(d) stratosphere-troposphere coupling, land-atmosphere coupling, ocean-atmosphere coupling,
(e) studies of predictability and predictive skill of atmospheric or surface variables such as sea ice, snow cover, and land surface,
(f) case studies of extreme or high-impact events,
(g) impact studies, applications, and climate services at the S2S timescale including, but not limited to, the areas of hydrology, health, fire, agriculture and food security, and energy.

This session covers predictions of climate from seasonal to decadal timescales and their applications. With a time horizon from a few months up a few decades, such predictions are of major importance to society, and improving them presents an interesting scientific challenge. This session embraces advances in our understanding of the origins of seasonal to decadal predictability, as well as in improving the forecast skill and making the most of this information by developing and evaluating new applications and climate services.

The session welcomes contributions from dynamical as well as statistical predictions (including machine learning methods) and their combination. This includes predictions of climate phenomena, including extremes, from global to regional scales, and from seasonal to multi-decadal timescales ("seamless predictions"). The session also covers physical processes relevant to long-term predictability sources (e.g. ocean, cryosphere, or land) and predictions of large-scale atmospheric circulation anomalies associated to teleconnections as well as observational and emergent constraints on climate variability and predictability. Also relevant is the time-dependence of the predictive skill and windows of opportunity. Analysis of predictions in a multi-model framework, and ensemble forecast initialization and generation, including innovative ensemble approaches to minimize initialization shocks, are another focus of the session. The session pays particular attention to innovative methods of quality assessment and verification of climate predictions, including extreme-weather frequencies, post-processing of climate hindcasts and forecasts, and quantification and interpretation of model uncertainty. We particularly invite contributions presenting the use of seasonal-to-decadal predictions for risk assessment, adaptation and further applications.

Statistical post-processing techniques for weather, climate, and hydrological forecasts are powerful approaches to compensate for effects of errors in model structure or initial conditions, and to calibrate inaccurately dispersed ensembles. These techniques are now an integral part of many forecasting suites and are used in many end-user applications such as wind energy production or flood warning systems. Many of these techniques are flourishing in the statistical, meteorological, climatological, hydrological, and engineering communities. The methods range in complexity from simple bias correction up to very sophisticated distribution-adjusting techniques that take into account correlations among the prognostic variables.

At the same time, a lot of efforts are put in combining multiple forecasting sources in order to get reliable and seamless forecasts on time ranges from minutes to weeks. Such blending techniques are currently developed in many meteorological centers. These forecasting systems are indispensable for societal decision making, for instance to help better prepare for adverse weather. Thus, there is a need for objective statistical framework for "forecast verification'', i.e. qualitative and quantitative assessment of forecast performance.

In this session, we invite presentations dealing with both theoretical developments in statistical post-processing and evaluation of their performances in different practical applications oriented toward environmental predictions, and new developments dealing with the problem of combining or blending different types of forecasts in order to improve reliability from very short to long time scales.

As the societal impacts of hazardous weather and other environmental pressures grow, the need for integrated predictions which can represent the numerous feedbacks and linkages between physical and chemical atmospheric processes is greater than ever. This has led to development of a new generation of high resolution multi-scale coupled prediction tools to represent the two-way interactions between aerosols, chemical composition, meteorological processes such as radiation and cloud microphysics.

Contributions are invited on different aspects of integrated model and data assimilation development, evaluation and understanding. A number of application areas of new integrated modelling developments are expected to be considered, including:

i) improved numerical weather prediction and chemical weather forecasting with feedbacks between aerosols, chemistry and meteorology,
ii) two-way interactions between atmospheric composition and climate variability.
This session aims to share experience and best practice in integrated prediction, including:
a) strategy and framework for online integrated meteorology-chemistry modelling;
b) progress on design and development of seamless coupled prediction systems;
c) improved parameterisation of weather-composition feedbacks;
d) data assimilation developments;
e) evaluation, validation, and applications of integrated systems.

This Section is organised in cooperation with the Copernicus Atmosphere Monitoring Service (CAMS) and the WMO Global Atmosphere Watch (GAW) Programme.
This year session is dedicated to the Global Air Quality Forecasting and Information Systems (GAFIS) - an initiative of WMO and several international organizations - to enable and provide science-based air quality forecasting and information services in a globally harmonized and standardized way tailored to the needs of society.

This session deals with atmospheric convection, being dry, shallow, or deep convection. Contributions on these aspects resulting from the use of large-eddy simulations, convection-permitting simulations, coarser-resolution simulations using parameterised convection and observations are welcome. Studies that investigate the organization of convection, being in idealized set-ups (radiative convective equilibrium and self-aggregation) or in observations, as well as studies that investigate the importance of organization for climate are welcome. Besides this, studies that investigate general aspects of convection such as processes controlling the lifecycle of convection, interactions of convection with other physical processes and representation of convection in numerical weather prediction and climate models, being for instance through the use of machine learning techniques, are also welcome.

The uncertain response of clouds to global warming is a major contributor to the spread in climate sensitivity across climate models. Cloud feedback uncertainty is related to a limited understanding of the coupling between clouds, convection and the large-scale circulation across various spatial and temporal scales. This session focuses on efforts to advance our understanding of the cloud-circulation coupling and its role in climate change. Contributions from dedicated field campaigns such as EUREC4A/ATOMIC, from various observing platforms like ground-based and satellite remote sensing or in situ measurements, as well as modelling and theoretical studies are welcomed. We also invite abstracts focusing on the role of convective organization, precipitation and aerosols in modulating the cloud-circulation coupling and cloud feedbacks.

Mesoscale and severe convection are known to be important precipitation producing processes over land. They are often associated with hazardous weather (e.g. damaging winds, hail, lightning, tornadoes, extreme precipitation and flooding), which we already see is becoming more frequent in many regions with climate change. At the same time, these storms remain difficult to predict throughout all lifecycle stages from initiation to upscale growth and dissipation.
The aim of this session is to gain an improved understanding of mesoscale and severe convective processes over land from a non-idealised perspective for current and future periods.
We invite contributions focussing on the underlying storm dynamics and microphysics, upscale effects, advances in modelling and predictability of these storm systems, and their impacts. We also invite contributions on the driving processes of the formation and evolution of severe convection, and how these factors explain spatio-temporal patterns of storm intensity, precipitation and on-the-ground hazards. This includes contributions on land-convection interactions in connection with mesoscale and severe storms, e.g. effects of complex topography, soil moisture feedbacks, or land use / land use change including e.g. urbanisation, deforestation or irrigation.
Contributions focussing on individual extreme events or giving climatological perspectives including future climates are welcome, as are studies relying on remote sensing data, in-situ observations, or high-resolution models, especially those that explicitly resolve convection.

Cold clouds (mixed-phase and ice) play an important role in the Earth’s radiation budget because of their high temporal and spatial coverage and their interaction with long wave and short wave radiation. Yet, the variability and complexity of their macro- and microphysical properties, the consequence of intricate ice particle nucleation and growth processes, makes their study extremely challenging. As a result, large uncertainties still exist in our understanding of cold cloud processes, their radiative effects, and their interaction with their environment (in particular, aerosols).

Solicited speaker: Greg McFarquhar, University of Oklahoma, Cooperative Institute for Severe and High Impact Weather Research and Operations, Norman, United States of America

This session will be back-to-back in coordination with session AS3.14 (Atmospheric surface-science and ice nucleating particles).
We also like to draw your attention to the following workshop pre-EGU giving more room for discussion:
https://www.tuwien.at/en/tch/pc/physical-chemistry-of-atmosphere/workshop

Clouds play an important role in the Polar climate due to their interaction with radiation and their role in the hydrological cycle linking poleward water vapour transport with precipitation. Cloud and precipitation properties depend on the atmospheric dynamics and moisture sources and transport, as well as on aerosol particles, which can act as cloud condensation and ice nuclei. These processes are complex and are not well represented in the models. While measurements of cloud and precipitation microphysical properties in the Arctic and Antarctic regions are challenging, they are highly needed to evaluate and improve cloud processes representation in the models used for polar and global climate and cryosphere projections.

This session aims at bringing together researchers using observational and/or modeling approaches (at various scales) to improve our understanding of polar tropospheric clouds, precipitation, and related mechanisms and impacts. Contributions are invited on various relevant processes including (but not limited to):
- Drivers of cloud/precipitation microphysics at high latitudes,
- Sources of cloud nuclei both at local and long range,
- Linkages of polar clouds/precipitation to the moisture sources and transport, including including extreme transport events (e.g., atmospheric rivers, moisture intrusions),
- Relationship of moisture/cloud/precipitation processes to the atmospheric dynamics, ranging from synoptic and meso-scale processes to teleconnections and climate indices,
- Interactions between clouds and radiation, including impacts on the surface energy balance,
- Impacts that the clouds/precipitation in the Polar Regions have on the polar and global climate system, surface mass and energy balance, sea ice and ecosystems.

Papers including new methodologies specific to polar regions are encouraged, such as (i) improving polar cloud/precipitation parameterizations in atmospheric models, moisture transport events detection and attribution methods specifically in the high latitudes, and (ii) advancing observations of polar clouds and precipitation. We would like to emphasize collaborative observational and modeling activities, such as the Year of Polar Prediction (YOPP), Polar-CORDEX, the (AC)3 project on Arctic Amplification, MOSAiC and other measurement campaigns in the Arctic and Southern Ocean/Antarctica and encourage related contributions.

Storm and convective-scale weather data analysis and prediction still present significant challenges for atmospheric sciences.
Addressing these challenges requires a synergy of advances in high-resolution observations, modeling, and data assimilation.
Especially assimilating satellite observations bears great potential for improving future storm-scale predictions.

This session invites contributions from developments in
● Convective-scale data assimilation techniques and models
● Active and passive satellite data assimilation
● Assessment of the impact of satellite and convective-scale data assimilation on prediction
● Model uncertainty representation in convective scale data assimilation
● Observations at convective scales: data products, observing strategies, observation operators, remote sensing, and new technologies
● Machine learning in convective scale data assimilation and forecasting

The understanding of tropical phenomena and their representation in numerical models still raise important scientific and technical questions, particularly in the coupling between the dynamics and diabatic processes. Among these phenomena, tropical cyclones (TC) are of critical interest because of their societal impacts and because of uncertainties in how their characteristics (cyclogenesis processes, occurrence, intensity, latitudinal extension, translation speed) will change in the framework of global climate change. The monitoring of TCs, their forecasts at short to medium ranges, and the prediction of TC activity at extended range (15-30 days) and seasonal range are also of great societal interest.

The aim of the session is to promote discussions between scientists focusing on the physics and dynamics of tropical phenomena. This session is thus open to contributions on all aspects of tropical meteorology between the convective and planetary scale, such as:

- Tropical cyclones,
- Convective organisation,
- Diurnal variations,
- Local circulations (i.e. island, see-breeze, etc.),
- Monsoon depressions,
- Equatorial waves and other synoptic waves (African easterly waves, etc.),
- The Madden-Julian oscillation,
- etc.

We especially encourage contributions of observational analyses and modelling studies of tropical cyclones and other synoptic-scale tropical disturbances including the physics and dynamics of their formation, structure, and intensity, and mechanisms of variability of these disturbances on intraseasonal to interannual and climate time scales.
Findings from recent field campaigns are also encouraged.

This session investigates mid-latitude to subtropical cyclones and storms on both hemispheres. We invite studies considering cyclones in different stages of their life cycles from the initial development, to large- and synoptic-scale conditions influencing their growth to a severe storm, up to their dissipation and related socioeconomic impacts. We also welcome studies investigating these weather systems and their climate controls in subtropical regions of both hemispheres.

Papers are welcome, which focus also on the diagnostic of observed past and recent trends, as well as on future storm development under changed climate conditions. This will include storm predictability studies on different scales. Finally, the session will also invite studies investigating impacts related to storms: Papers are welcome dealing with vulnerability, diagnostics of sensitive social and infrastructural categories and affected areas of risk for property damages. Which risk transfer mechanisms are currently used, depending on insured and economic losses? Which mechanisms (e.g. new reinsurance products) are already implemented or will be developed in order to adapt to future loss expectations?

ENSO and its interactions with other tropical basins are the dominant source of interannual climate variability in the tropics and across the globe. Understanding the dynamics, predictability, and impacts of ENSO and tropical basins interactions, and anticipating their future changes are thus of vital importance for society. This session invites contributions regarding all aspects of ENSO and tropical basins interactions, including: dynamics, multi-scale interactions; decadal and paleo variability; theoretical approaches; ENSO diversity; global teleconnections; impacts on climate, society and ecosystems; seasonal forecasting and climate change projections of tropical mean state changes, ENSO and its tropical basins interactions. Studies aimed at evaluating and improving model simulations of ENSO, the tropical mean state and the tropical basins interactions basin are especially welcomed.

Recent extreme weather and climate episodes, like the recurrent and concurrent summer heatwaves in the Northern Hemisphere or the flooding in Germany in summer 2021, highlight the need to further our understanding of linear and non-linear (quasi-stationary) planetary and synoptic-scale Rossby wave dynamics in the atmosphere, and their impacts on weather and climate events.

Abstracts are solicited that are dedicated to:
(1) The dynamics of linear wave propagation or quasi-stationarity, of wave breaking, atmospheric blocking, or jets as atmospheric Rossby waveguides. This includes the role of local and remote drivers (e.g., the tropics, Arctic, or stratosphere).
(2) Exploring the links between extreme weather/climate events and linear and non-linear Rossby waves, including wave breaking and/or blocking.
(3) Quantifying model representation of Rossby waves in climate and numerical weather prediction models, including wave propagation and breaking.
(4) Exploring the role of Rossby wave packets on predictability at lead times from medium range (~2 weeks) to seasonal time-scales. This includes blocking and wave propagation.
(5) Analyzing projected future changes in planetary or synoptic-scale Rossby waves, or in their future impacts on weather and climate events.

Regional climate is often influenced by or connected to changes in remote locations, a phenomenon known as a teleconnection. Changes in the ocean, sea ice, atmosphere or land conditions in remote locations can trigger atmospheric or oceanic disturbances, which then propagate and influence the climate in one or multiple distant regions. These changes could be periodic modes of variability (such as ENSO, IOD, QBO, AMV, PDV etc.) or a response to anthropogenic forcing (such as the warming Western Tropical Pacific or the North Atlantic Warming Hole etc.). Fleshing out the teleconnections associated with such changes provides us with a clearer understanding of the variations in the climate of a particular region and may also provide a source of predictability. This session invites contributions that focus on this aspect of climate variability and yield new understanding on the origin, dynamics and predictive potential of teleconnections. The studies may be observational or modelling in nature and may be based on paleoclimatic time-scales, the historical period or future scenarios. Research on new methods to diagnose and understand teleconnections is also welcome.

Atmospheric circulation is unquestionably listed among the fundamental causes of weather and climate. The session is dedicated to all aspects of relationships between atmospheric circulation in different spatial scales and climate as well as environmental variables. Contributions concerning theoretical aspects of circulation classifications development and their applications in various tasks (climatological, and environmental), and different scales are particularly welcome as well as submissions on recent climate variability and change studied by tools of synoptic climatology.

Internal gravity waves (IGWs) still pose major questions in the study of both atmospheric and ocean sciences, and stellar physics. Important issues include IGW radiation from their various relevant sources, IGW reflection at boundaries, their propagation through and interaction with a larger-scale flow, wave-induced mean flow, wave-wave interactions in general, wave breaking and its implications for mixing, and the parameterization of these processes in models not explicitly resolving IGWs. The observational record, both on a global scale and with respect to local small-scale processes, is not yet sufficiently able to yield appropriate constraints. The session is intended to bring together experts from all fields of geophysical and astrophysical fluid dynamics working on related problems. Presentations on theoretical, modelling, experimental, and observational work with regard to all aspects of IGWs are most welcome, including those on major collaborative projects, such as DataWave.

The atmospheric water cycle is a key component of the climate system, and links across many scientific disciplines. Processes interact with dynamics at different scales throughout the atmospheric life cycle of water vapour from evaporation to precipitation. This session sets the focus on understanding the interaction between processes, their dynamics and characteristics of the water cycle, covering the entire atmospheric life cycle from evaporation, atmospheric moisture transport, to cloud microphysics and precipitation processes as observed from in-situ and remote sensing instrumentation, recorded by (paleo)climate archives, and as simulated by models for past, present and future climates.

We invite studies

* focusing on the understanding and impacts of features of the atmospheric water cycle related to weather systems, such as Atmospheric Rivers, Cold-Air Outbreaks, Warm Conveyor Belts, Tropical Moisture Exports, and the global Monsoon systems;

* investigating the large-scale drivers behind the ongoing and future variability and trends within the atmospheric water cycle, from long-term observations, reanalysis data, regional to global model simulations, or (isotopic) data assimilation;

* involving and connecting field campaigns (YOPP, MOSAiC, (AC)3, ISLAS, EUREC4A, AWACA, LIAISE etc.) with forecast and reanalysis data, indicators of past hydroclimate from climate proxies such as ice cores and stalagmites, and model predictions of the future evolution of the atmospheric water cycle;

* applying methods such as tagged water tracers and Lagrangian moisture source diagnostics to identify source-sink relationships and to evaluate model simulations of the water cycle;

* using the isotopic fingerprint of atmospheric processes and weather systems to obtain new mechanistic insights into changes in the water cycle, to study exchanges between the earth surface and the atmosphere, how convection impacts cloudiness in the tropics, and how the isotopic signal from various archives can be used to reconstruct past climate variations;

* describing the global and regional state of the atmospheric water cycle with characteristics such as the recycling ratio, life time of water vapour, and moisture transport properties.

We particularly encourage contributions to link across neighbouring disciplines, such as atmospheric science, climate, paleoclimate, glaciology, and hydrology.

Traditionally, hydrologists focus on the partitioning of precipitation water on the surface, into evaporation and runoff, with these fluxes being the input to their hydrologic models. However, more than half of the evaporation globally comes back as precipitation on land, ignoring an important feedback of the water cycle if the previous focus applied. Land-use and water-use changes, as well as climate variability and change alter, not only, the partitioning of water but also the atmospheric input of water as precipitation, related with this feedback, at both remote and local scales.

This session aims to:
i. investigate the remote and local atmospheric feedbacks from human interventions such as greenhouse gasses, irrigation, deforestation, and reservoirs on the water cycle, precipitation and climate, based on observations and coupled modelling approaches,
ii. investigate the use of hydroclimatic frameworks such as the Budyko framework to understand the human and climate effects on both atmospheric water input and partitioning,
iii. explore the implications of atmospheric feedbacks on the hydrologic cycle for land and water management.

Typically, studies in this session are applied studies using fundamental characteristics of the atmospheric branch of the hydrologic cycle on different scales. These fundamentals include, but are not limited to, atmospheric circulation, humidity, hydroclimate frameworks, residence times, recycling ratios, sources and sinks of atmospheric moisture, energy balance and climatic extremes. Studies may also evaluate different sources of data for atmospheric hydrology and implications for inter-comparison and meta-analysis. For example, observations networks, isotopic studies, conceptual models, Budyko-based hydro climatological assessments, back-trajectories, reanalysis and fully coupled earth system model simulations.

This session explores the driving mechanism for the timing of a monsoon season, which is key for a number of climate-sensitive sectors such as agriculture, hydropower that are highly dependent on the spatial and temporal distribution of rainfall throughout the season. In particular, we welcome submissions advancing the link between large-scale atmospheric and oceanic systems and the timing of the onset. This session will also discuss the different definition of onset currently used by NMHS and regional climate institutes for various applications (e.g., agriculture, climate model analysis)
The session aims to bring together, amongst others, climate service providers, numerical modelers, observation community and other disciplines for onset is relevant (e.g. Hydrology, ecology and agriculture), with the aim of advancing the understanding of onset definitions and their driving mechanisms. Of particular interest are new insights on the dynamical drivers that control the timing of monsoon onset. For example: physical mechanisms, interannual and decadal variability, differences in climate change signal on onset, interactions across scales and land-atmosphere interactions. Further, we welcome studies that explore rainfall onset in a variety of contexts whether they be past, present or future change. Studies that move towards improving the forecast skill of onset at seasonal and sub-seasonal timescales are especially encouraged.

Additional topics include, though are not limited to:
- Monsoon systems under climate change
- Event based case studies (cases of very early and late onset)
- Interannual and decadal variability of rainfall in tropical regions
- Inclusion of onset in climate services in Africa
- Model evaluation on timing of onset
- Understanding the variability of onset dates on agriculture
- Coproduction of onset forecast for specific application

Regional monsoons and the global monsoon circulation to which they belong have profound impacts on water, energy, and food security. Monsoons cause severe floods and droughts as well as undergoing variability on subseasonal, interannual and decadal-to-multi-decadal time scales. In addition to profound local effects, monsoon variability is also associated with global-scale impacts via teleconnections.

Monsoons are among the most complex phenomena involving coupled atmosphere-ocean-land interactions and remain notoriously difficult to forecast at leads times ranging from numerical weather prediction (NWP) to long-term climate projections. A better understanding of monsoon physics and dynamics, with more accurate simulation, prediction and projection of monsoon systems is therefore of great importance.

This session invites presentations on any aspects of monsoon research in present-day, future and palaeoclimate periods, involving observations, modelling, attribution, prediction and climate projection. Topics ranging from theoretical works based on idealized planets and ITCZ frameworks to the latest field campaign results are also invited, as is work on impacts, extremes, NWP modelling, S2S and decadal forecasting, and the latest CMIP6 findings.

Precipitation, both liquid and solid, is a central element of the global water/energy cycle through its coupling with clouds, water vapor, atmospheric motions, ocean circulation, and land surface processes. Precipitation is also the primary source of freshwater, while it can have tremendous socio-economical impacts associated with extreme weather events such as hurricanes, floods, droughts, and landslides. Accurate and timely knowledge of precipitation characteristics at regional and global scales is essential for understanding how the Earth system operates under changing climatic conditions and for improved societal applications that range from numerical weather prediction to freshwater resource management. This session will host papers on all aspects of precipitation, especially contributions in the following four research areas: Precipitation Measurement: Precipitation measurements (amount, duration, intensity etc) by ground-based in situ sensors (e.g., rain gauges, disdrometers); estimation of accuracy of measurements, comparison of instrumentation. Precipitation Climatology: Regional and global climatology; areal distribution of measured precipitation; classification of precipitation patterns; spatial and temporal characteristics of precipitation; methodologies adopted and their uncertainties; comparative studies. Precipitation Remote Sensing: Remote sensing of precipitation (spaceborne, airborne, ground-based, underwater, or shipborne sensors); methodologies to estimate areal precipitation (interpolation, downscaling, combination of measurements and/or estimates of precipitation); methodologies used for the estimation (e.g., QPE), validation, and assessment of error and uncertainty of precipitation as estimated by remote sensors. A special focus will be on international contributions to the exploitation of the international Global Precipitation Measurement (GPM) mission and preparations for new missions, such as Atmospheric Observing System (AOS), EUMETSAT Polar System-Second Generation (EPS-SG), and Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS), as well as new space-borne instrumentation (AMSR-3).

The assessment of precipitation variability and uncertainty is crucial in a variety of applications, such as flood risk forecasting, water resource assessments, evaluation of the hydrological impacts of climate change, determination of design floods, and hydrological modelling in general. This session aims to gather contributions on research, advanced applications, and future needs in the understanding and modelling of precipitation variability, and its sources of uncertainty.

Contributions focusing on one or more of the following issues are particularly welcome:
- Novel studies aimed at the assessment and representation of different sources of uncertainty versus natural variability of precipitation.
- Methods to account for accuracy in precipitation time series due to, e.g., change and improvement of observation networks.
- Uncertainty and variability in spatially and temporally heterogeneous multi-source precipitation products.
- Estimation of precipitation variability and uncertainty at ungauged sites.
- Precipitation data assimilation.
- Process conceptualization and approaches to modelling of precipitation at different spatial and temporal scales, including model parameter identification and calibration, and sensitivity analyses to parameterization and scales of process representation.
- Modelling approaches based on ensemble simulations and methods for synthetic representation of precipitation variability and uncertainty.
- Scaling and scale invariance properties of precipitation fields in space and/or in time.
- Physically and statistically based approaches to downscale information from meteorological and climate models to spatial and temporal scales useful for hydrological modelling and applications.

Rainfall is a “collective” phenomenon emerging from numerous drops. Understanding the relation between the physics of individual drops and that of a population of drops remains an open challenge, both scientifically and at the level of practical implications. This remains true also for solid precipitation. Hence, it is much needed to better understand small scale spatio-temporal precipitation variability, which is a key driving force of the hydrological response, especially in highly heterogeneous areas (mountains, cities). This hydrological response at the catchment scale is the result of the interplay between the space-time variability of precipitation, the catchment geomorphological / pedological / ecological characteristics and antecedent hydrological conditions. Therefore, (1) accurate measurement and prediction of the spatial and temporal distribution of precipitation over a catchment and (2) the efficient and appropriate description of the catchment properties are important issues in hydrology.

This session will bring together scientists and practitioners who aim to measure and understand precipitation variability from drop scale to catchment scale as well as its hydrological consequences. Contributions addressing one or several of the following topics are especially targeted:
- Novel techniques for measuring liquid and solid precipitation variability at hydrologically relevant space and time scales (from drop to catchment scale), from in situ measurements to remote sensing techniques, and from ground-based devices to spaceborne platforms. Innovative comparison metrics are welcomed;
- Precipitation drop (or particle) size distribution and its small scale variability, including its consequences for precipitation rate retrieval algorithms for radars, commercial microwave links and other remote sensors;
- Novel modelling or characterization tools of precipitation variability from drop scale to catchment scale from various approaches (e.g. scaling, (multi-)fractal, statistic, deterministic, numerical modelling);
- Novel approaches to better identify, understand and simulate the dominant microphysical processes at work in liquid and solid precipitation.
- Applications of measured and/or modelled precipitation fields in catchment hydrological models for the purpose of process understanding or predicting hydrological response.

The Earth's mesosphere and lower thermosphere (MLT) region is a great platform to study ionospheric dynamics, disturbances, eddy mixing, and controlling parameters. This transition region is sandwiched between the lower and upper atmosphere, which is strongly driven by the forcing from both the above (e.g., solar and magnetospheric inputs) and below (e.g., gravity waves and atmospheric tides). The thermal structure of the MLT region is controlled by numerous sources and sinks of energy, including solar radiation, chemical, and dynamical processes. Solar atmospheric tides related to global-scale variations of winds and waves are responsible for coupling the lower and upper layers of the atmosphere. During this coupling process, the precipitation of energetic particles into the MLT region also greatly influences the vertical profiles of the temperature, chemistry, and dynamics of the upper atmosphere. This is an appropriate forum/time to encourage the scientific community to present, discuss, update, and improve our understanding of dynamics, chemistry, and coupling in the MLT region which ultimately affect the electrodynamics of the whole coupled geospace environment. This session invites presentations on scientific work related to various experimental/observational techniques, numerical and empirical modeling, and theoretical analyses on the dynamics, chemistry, and coupling processes in the altitude range of ~ 60 km – 180 km of the MLT regions.

The middle atmosphere is an important region of the atmosphere because variations in its dynamics, structure and composition impact the weather and climate at the surface. For example, changes in the normal circulation of the stratosphere either due to natural internal variability (e.g., SSWs, QBO) or due to changes in its chemical composition (e.g., CO2, O3) have a dynamical downward influence onto the troposphere in different regions and at various time scales. In addition, changes in the concentration of greenhouse gases can also impact the upper atmosphere (e.g., cooling, contraction). This session presents contributions that study and monitor these phenomena, understand their consequences, and predict their future evolution using various observational, theoretical, and modelling techniques.

The composition of the upper troposphere and the lower stratosphere (UTLS) plays a key role in the climate system. Our understanding of the interactions between dynamics, chemistry and climate in this region is rapidly advancing thanks to both observational and modelling studies. In this session, we invite presentations on dynamical, transport and chemical processes determining the variability and long-term trends in the composition of the UTLS, and related effects on radiation and dynamics. We particularly encourage contributions introducing recent observations (both in situ and remote sensing) as well as models of various complexity ranging from comprehensive chemistry climate models to idealized and conceptual models.

This year, special focus topics will include (1) the stratospheric aftermath of the historical Hunga Tonga-Hunga Ha'apai eruption in January 2022 and other extreme events (wildfires, volcanic eruptions), and (2) recent field experiments investigating the impact of summer monsoons and convective transport on the UTLS.

Hydro-meteorological extremes such as floods, droughts, storms, or heatwaves often affect large regions therefore causing large damages and costs. Hazard and risk assessments, aiming at reducing the negative consequences of such extreme events, are often performed with a focus on one location despite the spatially compounding nature of extreme events. While spatial extremes receive a lot of attention by the media, little is known about their driving factors and it remains challenging to assess their risk by modelling approaches. Key challenges in advancing our understanding of spatial extremes and in developing new modeling approaches include the definition of multivariate events, the quantification of spatial dependence, the dealing with large dimensions, the introduction of flexible dependence structures, the estimation occurrence probabilities, the identification of potential drivers for spatial dependence, and linking different spatial scales. This session invites contributions which help to better understand processes governing spatial extremes and/or propose new ways of describing and modeling spatially compounding events at different spatial scales.

Extreme climate events have significant impacts on the environment and society. During recent decades, extreme climate events such as heatwaves, floods, droughts, extreme temperatures, heavy snowfall, and rainstorms have frequently occurred across the globe. These events have caused numerous casualties and enormous economic loss.
So far, the interannual-interdecadal variability and the long-term trend of extreme climate events have not been well understood. An important reason is that the mechanisms of extreme climate events are complex. For example, the tropical air-sea interaction, particularly ENSO, may induce flooding and/or droughts in Asia, North America, and Australia during summertime. Rapid changes in the Arctic climate including sea ice loss may induce cold surges and intense snowfall events in the mid-latitudes during the winter. However, the relationship between tropical air-sea interactions, polar climatic changes, and the occurrence of extreme climate events is poorly understood.
In addition, currently the prediction of extreme climate events is mostly poor. Better prediction of extreme climate events is urgently needed for public, which is particularly vital for decision-makers and stakeholders to devise appropriate and informed plans regarding climate change adaptation and climate disaster warning systems.
Thus, the aim of this session is to obtain a better understanding of the variability, mechanisms, and prediction of extreme climate events. We invite papers focusing on the historical changes of extreme climate events, the influences of air-sea-ice-land interaction on extreme climate events, and near-term prediction and projection of extreme climate events. Moreover, papers related to the observation, numerical simulation, attribution, and impacts of extreme climate events are also appreciated.

This session explores climate change, extremes, processes and their impacts at local to regional scales, and the tools employed to investigate these phenomena. In particular, we welcome submissions advancing the state-of-the-art in the development and application of high-resolution models (convection-permitting, grid spacing ≤ 4 km) and high-resolution sub-daily data sets. Other high-resolution data sets such as land-surface, hydrology, vegetation or similar, and their impacts on local-scale climate change and extremes, are of further interest.

The session aims to bring together, amongst others, numerical modellers, the observational community and CORDEX-FPS participants, with the aim of advancing understanding of the aforementioned topics. Of particular interest are new insights which are revealed through high-spatiotemporal-resolution modelling or data sets. For example: convective extremes, physical mechanisms, fine-scale and feedback processes, differences in climate change signal, scale-dependency of extremes, interactions across scales and land-atmosphere interactions. Further, we welcome studies that explore local scale climate change in a variety of contexts whether they be past, present or future change. Studies that move towards an earth system approach – through incorporating coupled oceans, hydrology or vegetation – are especially encouraged.

Additional topics include, though are not limited to:
-- Mesoscale convective systems and medicanes
-- Event-based case studies (including surrogate climate change experiments or attribution)
-- Approaches for quantifying uncertainty at high resolutions including multi-model ensemble and combined dynamical-statistical approaches such as emulators
-- High-resolution winds and their impacts
-- Convection, energy balance and hydrological cycle including vegetation
-- Model setup and parametrization, including sensitivity to resolution, land surface and dynamics
-- Tropical convection and convective processes at local to regional scale
-- Model evaluation and new evaluation metrics/methods
-- Physical understanding of added value over coarser models
-- Severe storms including supercell thunderstorms and hailstorms
-- The roles of natural and internal variability

Recent extreme events with intensities unprecedented in the observational record are causing high impacts globally, such as the heat waves in the UK, Pacific Northwest and in parts of China and severe flooding in Pakistan, Western Europe, eastern US and across China. Some of these events would have arguably been nearly impossible without human-made climate change and broke records by large margins. Furthermore, compound behaviour, cascading effects and complex risks are becoming evident, such as the spike in food prices induced by the effects of the war in Ukraine on top of concurrent drought across regions with subsequent crop failure. Finally, continuing warming potentially increases the risk of crossing tipping points and triggering abrupt changes. In order to increase preparedness for high impact climate events, it is important to develop methods and models that are able to represent these events and the impacts from them, and to better understand how to reduce the risks.

This session aims to bring together the latest research on modelling, understanding and managing plausible past and future high impact climate events. We are interested in rare and low-probability heavy precipitation events, droughts, floods, storms and temperature extremes from time scales of hours to decades, including compound, cascading, and connected extremes, as well as the effect of tipping points and abrupt changes driven by climate change, societal response, or other mechanisms (e.g., volcanic eruption). We are interested both in these events from the perspective of the interactive earth system per se, and on their impacts, consequences, and management perspectives.

We welcome a wide variety of methods to quantify and understand high-impact climate events in the present and future climate, such as through model experiments and intercomparisons; insights from paleo archives; climate projections (including large ensembles, and unseen events); attribution studies; and the development of storylines. We invite work on tipping elements/tipping points; abrupt changes; worst case scenarios; identification of adaptation limits; and the opportunities and solutions to manage the greatest risks.

This session is informed by the World Climate Research Programme lighthouse activities on Safe Landing Pathways and Understanding High-Risk Events.

ESA’s Aeolus satellite observations are expected to have the biggest impact for the improvement of numerical weather prediction in the Tropics. An especially important case relating to the evolution, dynamics, and predictability of tropical weather systems is the outflow of Saharan dust, its interaction with cloud microphysics and impact on tropical convection over the Atlantic Ocean.

The Joint Aeolus Tropical Atlantic Campaigns 2021 and 2022 (JATAC) deployed on Cabo Verde and the US Virgin Islands has a specific scientific focus on studying the Saharan Aerosol layer, African Easterly Waves and Jet, Tropical Easterly Jet, as well as the deep convection in the Intertropical Convergence Zone. These objectives relate to the genesis and life cycle of convective systems, the long-range transport of dust and its impact on air quality, and the satellite calibration/validation and preparation of future ESA and NASA missions(Aeolus, EarthCARE, AOS, WIVERN).

JATAC is building on a combination of ESA, NASA and national activities, joining several airborne and ground-based activities providing a unique scientific dataset to address the dynamics and composition in the Tropical Atlantic. This includes extensive observations by ground-based and airborne wind and aerosol lidars, Doppler radars, in-situ observations, as well as drop- and radiosondes. This is complemented by modelling activities, including data assimilation and detailed analysis by numerical weather prediction models.

The polar climate system is strongly affected by interactions between the atmosphere and the cryosphere. Processes that exchange heat, moisture and momentum between land ice, sea ice and the atmosphere, such as katabatic winds, blowing snow, ice melt, polynya formation and sea ice transport, play an important role in local-to-global processes. Atmosphere-ice interactions are also triggered by synoptic weather phenomena such as cold air outbreaks, polar lows, atmospheric rivers, Foehn winds and heatwaves. However, our understanding of these processes is still incomplete. Despite being a crucial milestone for reaching accurate projections of future climate change in Polar Regions, deciphering the interplay between the atmosphere, land ice and sea ice on different spatial and temporal scales, remains a major challenge.

This session aims at showcasing recent research progress and augmenting existing knowledge in polar meteorology and climate and the atmosphere-land ice-sea ice coupling in both the Northern and Southern Hemispheres. It will provide a setting to foster discussion and help identify gaps, tools, and studies that can be designed to address these open questions. It is also the opportunity to convey newly acquired knowledge to the community.

We invite contributions on all observational and numerical modelling aspects of Arctic and Antarctic meteorology and climatology, that address atmospheric interactions with the cryosphere. This may include but is not limited to studies on past, present and future of:
- Atmospheric processes that influence sea-ice (snow on sea ice, sea ice melt, polynya formation and sea ice production and transport) and associated feedbacks,
- The variability of the polar large-scale atmospheric circulation (such as polar jets, the circumpolar trough and storm tracks) and impact on the cryosphere (sea ice and land ice),
- Atmosphere-ice interactions triggered by synoptic and meso-scale weather phenomena such as cold air outbreaks, katabatic winds, extratropical cyclones, polar cyclones, atmospheric rivers, Foehn winds and heatwaves,
- Role of clouds in polar climate and impact on the land ice and sea ice through interactions with radiation,
- Teleconnections and climate indices and their role in land ice/sea ice variability.

Analysis of energy transfers between and within climate components has been at the core of many step changes in the understanding of the climate system. Large-scale atmospheric circulation, hydrological cycle and heat/moisture transports are tightly intertwined. Dynamics and radiative exchanges are linked at the global scale, through the net impact of cloud feedbacks, sea-ice albedo changes, surface absorption by vegetation.

In the Tropics, the zonal mean Hadley circulation determines meridional energy transports, while Rossby and planetary-scale waves modulate the energy exchanges carried by extratropical eddies. In the ocean, the role of Atlantic Meridional Overturning Circulation is essential for the heat budget of continental regions in the Northern Hemisphere: long-term oceanic and sea-ice variability is crucial to understand and predict the dynamics in high latitudes. Observational and model studies have indeed shown that the Arctic is very susceptible to climate change, and climate perturbations in the Arctic likely have wide-spread influence. High-latitude atmosphere, biosphere, oceans and cryosphere have experienced significant changes over the observational era. Hence, advancing the understanding of variability and change, governing mechanisms and global implications, improving predictions and projections of high latitude climate in both hemispheres is highly important for global society.

We invite submissions on the interplay between Earth’s energy exchanges and the general circulation through modeling, theory, and observations, on the forced response and natural variability of the general circulation, understanding present-day climate, past and future changes, impacts of global features and change on regional climate. This session also aims to improve knowledge and representation of the multi-scale mechanisms that control high-latitude climate variability and predictability in both hemispheres from sub-seasonal to multi-decadal and longer time scales. We thus invite contributions on the causes, mechanisms and climate feedbacks associated with the Arctic and Antarctic climate, ocean and sea ice change, including the potential links of the pronounced Arctic amplification to weather and climate outside the Arctic, and teleconnections of high latitude climate with lower latitude climate. We also aim to link climate variability, predictions and projections to potential ecosystem and socio-economic impacts and encourage submissions on this topic.

Abstracts are solicited related to the understanding and prediction of weather, climate and geophysical extremes, from both an applied and theoretical viewpoint.

In this session we propose to group together the traditional geophysical sciences and more mathematical/statistical and impacts-oriented approaches to the study of extremes. We aim to highlight the complementary nature of these viewpoints, with the aim of gaining a deeper understanding of extreme events. This session is a contribution to the EDIPI ITN, XAIDA and CLINT H2020 projects, and we welcome submissions from both project participants and the broader scientific community.

Potential topics of interest include but are not limited to the following:

· Dynamical systems theory and other theoretical perspectives on extreme events;
· Data-driven approaches to study extreme events, incl. machine learning;
· Representation of extreme events in climate models;
· Downscaling of weather and climate extremes;
· How extremes have varied or are likely to vary under climate change;
· Attribution of extreme events;
· Early warning systems and forecasts of extreme events;
· Linking the dynamics of extreme events to their impacts.

A global increase in the occurrence of extreme wildfire events urges the need to understand how fires respond to weather and climate variability at a spectrum of scales. In particular, 2022 European heatwaves triggered extreme wildfire conditions across the continent, setting off the alarms and raising questions about how devastating future fire seasons will be. Across many regions, future increases on current fire extremes will also bring significant ecological and societal impacts.

This session aims to bring together researchers from a range of disciplines to explore the changing meteorological and climatological dynamics of extreme wildfires along with their impacts on societies and ecosystems, spanning from atmospheric and fire turbulence to longer term climate interactions including future projections of climate change, and impacts of changing fire regimes such as on air quality, post-vegetation, or economic damage. This session welcomes observation and modelling research advancing our knowledge in weather and climate dynamics influencing extreme wildfire behaviour and their impacts, such as:

• Observational studies investigating impacts of weather processes on fire behaviour
• Numerical weather modelling studies for understanding weather processes influencing extreme fire behaviour
• Coupled numerical weather and fire spread modelling studies modulating fire behaviour across atmospheric scales
• Case studies of past wildfire events
• Global and regional modelling of present-day or future wildfire extremes and their impacts.
• Advances in fire behaviour modelling and prediction

Lagrangian tools allow to predict the dispersion of pollutants and track their sources, capture unresolved physics, and reveal transport pathways and barriers between flow regimes of fluid parcels that have different dynamical fates. As such, Lagrangian tools are used in a vast array of applications in geophysical fluid dynamics, from turbulent scales to planetary scales.

This session brings together scientists with experimental, numerical, and theoretical backgrounds.

Latest advancements will be presented on the following topics:
• Mesoscale to planetary-scale studies of transport and mixing (e.g. the AMOC, mixing in the surface ocean, identification of eddies and transport barriers);
• Tracking anthropogenic and natural influence (e.g. spread of microplastics, oil spills, volcanic ashes, and diseases);
• Micro-scale studies of turbulent flows (e.g. bubbles in the ocean surface layer, turbulence in the ocean and atmosphere);
• Tool development and numerical advances (e.g. use of machine learning, dynamic mode decomposition, trajectory rotation average, effects of model resolution);

Lightning is the energetic manifestation of electrical breakdown in the atmosphere, occurring as a result of charge separation processes operating on micro and macro-scales, leading to strong electric fields within thunderstorms. Lightning is associated with tropical storms and severe weather, torrential rains and flash floods. It has significant effects on various atmospheric layers and drives the fair-weather electric field. It is a strong indicator of convective processes on regional and global scales, potentially associated with climate change. Thunderstorms and lightning are also associated with the production of energetic radiation up to tens of MeV on time scales from sub-millisecond (Terrestrial Gamma-ray Flashes) to tens of seconds (gamma-ray glows).

This session seeks contributions from research in atmospheric electricity with emphasis on:

Atmospheric electricity in fair weather and the global electrical circuit
Effects of dust and volcanic ash on atmospheric electricity
Thunderstorm dynamics and microphysics
Middle atmospheric Transient Luminous Events
Energetic radiation from thunderstorms and lightning
Experimental investigations of lightning discharge physics processes
Remote sensing of lightning and related phenomena by space-based sensors
Thunderstorms, flash floods, tropical storms and severe weather
Modeling of thunderstorms and lightning
Now-casting and forecasting of thunderstorms using machine learning and AI
Regional and global lightning detection networks
Lightning Safety and its Societal Effects

Driven by atmospheric turbulence, and integrating surface processes to free atmospheric conditions, the Atmospheric Boundary Layer (ABL) plays a key role not only in weather and climate, but also in air quality and wind/solar energy. It is in this context that this session invites theoretical, numerical and observational studies ranging from fundamental aspects of atmospheric turbulence, to parameterizations of the boundary layer, and to renewable energy or air pollution applications. Below we propose a list of the topics included:

- Observational methods in the Atmospheric Boundary Layer
- Simulation and modelling of ABL: from turbulence to boundary layer schemes
- Stable Boundary Layers, gravity waves and intermittency
- Evening and morning transitions of the ABL
- Convective processes in the ABL
- Boundary Layer Clouds and turbulence-fog interactions
- Micro-Mesoscale interactions
- Micrometeorology in complex terrain
- Agricultural and Forest processes in the ABL
- Diffusion and transport of constituents in the ABL
- Turbulence and Air Quality applications
- Turbulence and Wind Energy applications

Solicited talks:
- Dr. Joan Cuxart, Universitat de les Illes Balears, Spain: Evapotranspiration: spatial variability in semiarid terrain at the sub-daily scale.

- Dr. Volker Wulfmeyer, University of Hohenheim, Germany: Studies of land-atmosphere feedback with a new synergy of observing systems.

This session is intended to provide an interdisciplinary forum to bring together researchers working in the areas of high-latitude meteorology, atmospheric chemistry, air quality, biogeochemistry, stable isotope research, oceanography, and climate.

The emphasis is on the role of boundary layer processes that mediate exchange of heat, momentum and mass between the Earth's surface (snow, sea-ice, ocean and land) and the atmosphere as well as the local to large-scale influences on these exchanges. An adequate understanding and quantification of these processes is necessary to improve modeling and prediction of future changes in the polar regions and their teleconnections with mid-latitude weather and climate, including meridional transport of heat, moisture, chemical trace species, aerosols and isotopic tracers; and regional emission and vertical mixing of climate active trace gases and aerosol, such as cloud-forming particles (CCN/INP) and their precursors.
It is expected that the recent implementation of new measurements such as those from pan-Arctic water vapor isotope networks, observations such as those obtained during the ALPACA and MOSAiC field campaigns, data from existing networks, and modeling efforts, e.g. within CRiceS and PolarRES, will help diagnose long-range and local moisture and aerosol sources as well as the coupling between local and large-scale dynamics and their impacts on climate, health and ecosystems.

We encourage submissions such as (but not limited to):
(1) External controls on the boundary layer such as clouds, radiation and long-range transport processes
(2) Results from field programs, such as ALPACA and MOSAiC, and routine observatories, insights from laboratory studies, and advances in modeling and reanalysis,
(3) Use of data from pan-Arctic and Antarctic observing networks,
(4) Surface processes involving snow, sea-ice, ocean, land/atmosphere chemical and isotope exchanges, and natural aerosol sources
(5) Studies on atmospheric chemistry and air pollution studies in the polar winter
(6) The role of boundary layers in polar climate change and implications of climate change for surface exchange processes, especially in the context of reduced sea ice, wetter snow packs, increased glacial discharge and physical and chemical changes associated with an increasing fraction of first year ice and increasing open water.

Air-sea interactions play a key role in the climate system. The ocean and atmosphere are intricately linked through the exchanges of momentum, mass, and energy. This drives processes on a wide range of spatial and temporal scales, from localised extreme events to the global climate. Air-sea interactions can dramatically impact extreme events such as tropical cyclones, marine heat waves, high precipitation events, and sea storms. They also shape the large-scale oceanic and atmospheric circulation affecting, for example, mesoscale eddies, Western Boundary Currents, convective precipitation, the Intertropical Convergence Zone, and ocean CO2 uptake. The complexity of air-sea interactions makes it hard to disentangle the different mechanisms at play, identify the driving processes, and properly model and parametrize them. This often results in widespread and persistent biases in coupled ocean-atmosphere models. Improving our knowledge of the physical and biogeochemical processes involved, through modeling or observations, is of fundamental importance to deepen our understanding of the Earth system and to improve the reliability of future projections as well as weather and ocean forecasts. This session aims to gather research efforts on air-sea interaction on global and regional scales over multiple temporal scales from interdisciplinary studies, modeling efforts, satellite, and in situ observations. This includes but is not limited to: turbulent air-sea fluxes, mesoscale eddies impact on CO2 fluxes, SSTs coupling with the atmospheric dynamic, tropical cyclones and cyclogenesis, extreme events onset, intensification and decay, parametrization of air-sea interactions, biases in coupled models, thermal and currents feedback, sea-spray role in air-sea exchanges and cloud formation.

The session is addressed to experimentalists and modellers working on air-land interactions from local to regional scales, in vegetated and/or urban systems. The programme is open to a wide range of new studies in micrometeorology and related atmospheric and remote sensing disciplines. The topics include the development of new devices, measurement techniques, experimental design, data analysis methods, as well as novel findings on surface layer theory and parametrization, including local and non-local processes. The theoretical parts encompass soil-vegetation-atmosphere transport, internal boundary-layer theories and flux footprint analyses. Of special interest are synergistic studies employing experimental data, parametrizations and models. This includes energy and trace gas fluxes (inert and reactive) as well as water, carbon dioxide and other GHG fluxes. Specific focus is given to outstanding problems in land surface boundary layer descriptions such as complex terrain, effects of horizontal heterogeneity on sub-meso-scale transport processes, energy balance closure, stable stratification and night time fluxes, dynamic interactions with atmosphere, plants (in canopy and above canopy) and soils.

Land–atmosphere interactions often play a decisive role in shaping climate extremes. As climate change continues to exacerbate the occurrence of extreme events, a key challenge is to unravel how land states regulate the occurrence of droughts, heatwaves, intense precipitation and other extreme events. This session focuses on how natural and managed land surface conditions (e.g., soil moisture, soil temperature, vegetation state, surface albedo, snow or frozen soil) interact with other components of the climate system – via water, heat and carbon exchanges – and how these interactions affect the state and evolution of the atmospheric boundary layer. Moreover, emphasis is placed on the role of these interactions in alleviating or aggravating the occurrence and impacts of extreme events. We welcome studies using field measurements, remote sensing observations, theory and modelling to analyse this interplay under past, present and/or future climates and at scales ranging from local to global but with emphasis on larger scales.

Ocean-atmosphere flux exchanges of biogeochemically active constituents have significant impacts on global biogeochemistry and climate. Increasing atmospheric deposition of anthropogenically-derived nutrients (e.g., nitrogen, phosphorus, iron) to the ocean influences marine productivity and has associated impacts on oceanic CO2 uptake, and emissions to the atmosphere of climate active species (e.g., nitrous-oxide (N2O), dimethyl-sulfide (DMS), marine organic compounds and halogenated species). Atmospheric inputs of toxic substances (e.g., lead, mercury, cadmium, copper, persistent organic pollutants) into the ocean are also of concern for their impact on ocean ecosystem health. In recent decades the intensive use of plastics has led to significant levels of persistent micro- and nano- plastics being transported into the marine atmosphere and to the ocean, with considerable uncertainty remaining on transport pathways and oceanic impacts. Other influential recent changes include emission reductions for air pollution abatement which have resulted in changes in cloud and aerosol chemical composition, affecting atmospheric acidity, associated chemical processing and impacts via atmospheric deposition on ocean biogeochemistry.

In turn, oceanic emissions of reactive species and greenhouse gases influence atmospheric chemistry and global climate, and induce potentially important chemistry-climate feedbacks. While advances have been made by laboratory, field, and modelling studies over the past decade, we still lack understanding of many of the physical and biogeochemical processes linking atmospheric deposition of chemicals, nutrient availability, marine biological productivity, trace-gas sources and sinks and the biogeochemical cycles governing air-sea fluxes of these climate active species, as well as on the atmosphere-ocean cycle of microplastics and its impact on the environment and climate.
This session will address the above issues on the atmospheric deposition of nutrients and toxic substances to the ocean, the impacts on ocean biogeochemistry, and also the ocean to atmosphere fluxes of climate active species and potential feedbacks to climate. We welcome new findings from measurement programmes (laboratory, in-situ and remote sensing) and atmospheric and oceanic numerical models.
This session is jointly sponsored by GESAMP Working Group 38 on ‘The Atmospheric Input of Chemicals to the Ocean’ and the Surface Ocean-Lower Atmosphere Study (SOLAS).

Aerosol particles are key components of the earth system; important in dictating radiative balance, human health, and other areas of key societal concern. Understanding their formation, evolution and impacts relies on developments from multiple disciplines covering both experimental laboratory work, field studies and numerical modeling. In this general session all topics of Aerosol Chemistry and Physics are covered. Contributions from aerosol laboratory, field, remote sensing and model studies are all highly encouraged.
Alongside general contributions, this year we also propose a focus on the importance and impact of aerosols in future climate scenarios. As we move towards a net-zero society, there is increasing pressure to reduce global carbon emissions. Across the world, multiple countries have begun to make ambitious commitments, including decarbonisation of multiple sectors. However, we need to avoid the unintended consequences of ‘carbon myopia’, where changes in policy lead to both desired and unexpected changes in atmospheric composition and thus impacts on multiple earth systems and human health. We thus invite submissions that fall within this broad topic. This could include:
• Evaluating the performance of current aerosol parameterisations in global climate models.
• Aerosol-cloud interactions and radiative transfer.
• Development of new methods to fuse heterogenous data sources with process models for improved climate projections.
• Advances in sampling technologies for source and process apportionment.
• Co-benefits assessment of clean air and carbon emission reduction for ecosystems and health under climate change.

Clouds and aerosols play a key role in climate and weather-related processes over a wide range of spatial and temporal scales. An initial forcing due to changes in the aerosol concentration and composition may also be enhanced or dampened by feedback processes such as modified cloud dynamics, surface exchange or atmospheric circulation patterns. This session aims to link research activities in observations and modelling of radiative, dynamical and microphysical processes of clouds, aerosols, and their interactions. Studies addressing several aspects of the aerosol-cloud-radiation-precipitation system are encouraged. Contributions related to the EU project “Constrained aerosol forcing for improved climate projections (FORCeS) are also invited.

Topics covered in this session include, but are not limited to:
- Cloud and aerosol macro- and microphysical properties, precipitation formation mechanisms and their role in the energy budget
- Observational constraints on aerosol-cloud interactions
- Use of observational simulators to constrain aerosols, clouds and their radiative effects in models
- Experimental cloud and aerosol studies
- High-resolution modelling, including large-eddy simulation and cloud-resolving models
- Parameterization of cloud and aerosol microphysics/dynamics/radiation processes
- Interactions between aerosols and regional circulation systems and precipitation patterns
- Aerosol, cloud and radiation interactions and feedbacks on the hydrological cycle, regional and global climate

The radiation budget of the Earth is a key determinant for the genesis and evolution of climate on our planet and provides the primary energy source for life. Anthropogenic interference with climate occurs first of all through a perturbation of the Earth radiation balance. We invite observational and modelling papers on all aspects of radiation in the climate system. A specific aim of this session is to bring together newly available information on the spatial and temporal variation of radiative and energy fluxes at the surface, within the atmosphere and at the top of atmosphere. This information may be obtained from direct measurements, satellite-derived products, climate modelling as well as process studies. Scales considered may range from local radiation and energy balance studies to continental and global scales. In addition, related studies on the spatial and temporal variation of cloud properties, albedo, water vapour and aerosols, which are essential for our understanding of radiative forcings, feedbacks, and related climate change, are encouraged. Studies focusing on the impact of radiative forcings on the various components of the climate system, such as on the hydrological cycle, on the cryosphere or on the biosphere and related carbon cycle, are also much appreciated.

Chemistry and aerosols play a major role in determining surface air quality, the Earth’s energy budget, and climate change. Conversely, climate change affects atmospheric abundances of trace gases and aerosols through composition-climate interactions. This session focuses on global scale atmospheric chemistry and aerosol modelling, radiative forcing, and climate change through the historical period and into the future. In particular, it aims to bring together scientists with an interest in:

• evaluating reactive gases and aerosols in models against observations
• quantifying the impact of emissions changes on atmospheric composition
• exploring chemistry-climate interactions in models, with a focus on climate feedbacks involving trace gases and aerosols
• quantifying radiative forcing and the climate response to changes in trace gas and aerosol concentrations
• the contribution of biogenic emissions to the climate impact of trace gas and aerosol concentrations
• evaluating regional trends in temperature, hydroclimate, and extreme events driven by aerosol changes

The session welcomes contributions from those currently involved in analysis of recent and ongoing CMIP6 experiments focusing on the areas above, and invites submission of abstracts in the following areas:
• Global and regional evaluation of CMIP, CCMI and HTAP models and variability across different spatial and temporal scales.
• The effects of aerosols on decadal climate variability, extremes, and teleconnections, and their interactions with modes of variability
• Modelling studies to understand the cause and impact of changes in atmospheric composition in the past and future periods
• Quantification of radiative forcing and feedbacks in models, including the roles of chemistry and aerosols
• Use of observational constraints to constrain relevant processes and interactions
• Emulation of complex atmospheric processes using statistical, process-based or AI techniques to reduce computational overhead

We particularly welcome contributions from the global and regional modelling and observation communities to these discussions. We also encourage studies focusing on climate risk and concrete regional impacts on nature and society resulting from changes in aerosol emissions.

The session will cover all aspects of polar stratospheric ozone, other species in the polar regions as well as all aspects of polar stratospheric clouds. Special emphasis is given to results from recent polar campaigns, including observational and model studies.

We encourage contributions on chemistry, microphysics, radiation, dynamics, small and large scale transport phenomena, mesoscale processes and polar-midlatitudinal exchange. In particular, we encourage contributions on ClOx/BrOx chemistry, chlorine activation, NAT nucleation mechanisms, on transport and mixing of processed air to lower latitudes and on the impact of wildfires and volcanic eruptions on polar ozone and polar stratospheric clouds.

We welcome contributions on polar aspects of ozone/climate interactions, including empirical analyses and coupled chemistry/climate model results and coupling between tropospheric climate patterns and high latitude ozone as well as representation of the polar vortex and polar stratospheric ozone loss in global climate models.

We particularly encourage contributions from the polar airborne field campaign as well as related activities, which aim at providing new scientific knowledge on the Arctic/Antarctic lowermost stratosphere and upper troposphere in a changing climate. Contributions from WMO's Global Atmosphere Watch (GAW) Programme and from the Network for the Detection of Atmospheric Composition Change (NDACC) are also encouraged.

The Paris Agreement on Climate sets the international objective to keep climate warming well below two degrees. This extraordinary challenge requires a dramatic improvement of current scientific capabilities to estimate the budgets and their trends of greenhouse gases (GHG) at regional scale, and how they link up to the global growth rates of the major GHGs (N2O, CH4 and CO2). This session aims to bring together studies to help understand and quantify regional budgets, trends and variability, and drivers of major GHG (N2O, CH4 and CO2) through the analyses of emissions inventories, field and remotely-sensed observations, terrestrial and ocean biogeochemical modeling, and atmospheric inverse modeling. We encourage contributions from the REgional Carbon Cycle Assessment and Processes (RECCAP2), a new global assessment of the Global Carbon Project, as well as studies combining different datasets and approaches at multi-scales from regional to global.

AS3.8A) Bioaerosols: detection, measurements, modelling and impacts
Primary bioaerosol particles span a wide range of sizes from tens of nm to up to 100µm. While these particles make a small contribution to the total aerosol number they contribute significantly to the total mass, with biological aerosol accounting for 15-25% of the total aerosol mass burden. The detection and classification of bioaerosol remains a significant technical challenge, where real-time methods capable of high temporal resolution are often limited by their discriminative capabilities, and offline methods which provide detailed speciation suffer from poor time resolution and difficulties in producing atmospheric concentrations. As such, accurately quantifying bioaerosol and understanding their impacts is of importance to an increasingly diverse range of research communities as they pose scientific questions relating to their influence on climate via cloud-aerosol interactions; the effects of allergenic species on public health and air quality and how this may be impacted by changes introduced by net zero policy; the agricultural health security impacts of pathogenic species; and the efficacy of early warning capabilities for national security and defence.

AS3.8B) Molecular Scale Characterisation of Aerosol and Cloud Particles
The large uncertainty associated with regional and global anthropogenic climate change is deeply rooted in our limited understanding of molecular scale processes occurring in aerosol particles and cloud droplets, which ultimately affect cloud properties and their climate impacts via modulating particle formation and growth. Atomistic scale properties of single aerosol particles, their interactions with the surrounding vapour phase molecules as well as transport processes within the particle phase typically occur on temporal and spatial scales which are attainable only by a handful of techniques. Molecular simulations (molecular dynamics and Monte Carlo) and single molecule experiments are promising methods with uniquely high spatial and temporal resolution which can complement traditional experimental and modelling approaches. Their recent emergence as tools to characterise molecular scale properties is catalysing the development of a new interdisciplinary field at the interface of molecular modelling and aerosol science, which can help address long-standing problems in new particle formation, gas-to-particle partitioning and heterogeneous nucleation.

In recent years, microplastics and nanoplastics have become recognised as ubiquitous atmospheric pollutants in the boundary layer. However, many open questions remain regarding emissions, transport and deposition of microplastics and nanoplastics, along with atmospheric processes they may be involved in while airborne. In this session we welcome contributions from observational, laboratory and modelling studies that advance the field of airborne microplastics and nanoplastics research, including:

- Sampling and analysis of airborne micro- and nanoplastics
- Atmospheric microplastics and nanoplastics and their interactions with different environmental compartments (oceans, land and the cryosphere)
- Contributions of soils, roads and other terrestrial sources to the atmospheric micro- and nanoplastic burden
- Ocean-atmosphere exchange of microplastics and nanoplastics
- Interactions between micro- and nanoplastics and other sources of aerosol
- Interactions between microplastics, nanoplastics, radiation and clouds
- Airborne microplastics as vectors for chemical and pathogen transport
- Indoor, outdoor, urban, rural and remote microplastics and nanoplastics (measurements, observations, modelling)
- Toxicological and exposure studies related to airborne micro- and nanoplastics
- Degradation of macro-, micro- and nanoplastics in real and simulated atmospheric conditions
- Airborne sources and sinks of micro- and nanoplastics (measurements and modelling)

Reactive halogen species can have an important influence on the chemistry of the troposphere. For instance, chlorine atoms react faster with most hydrocarbons than OH does and inorganic bromine and iodine can catalytically destroy tropospheric ozone and oxidise mercury. These reactions have been shown to be important in in environments as different as the polar troposphere during the springtime ozone depletion events, the boundary layer over salt lakes, and volcanic plumes. There is strong evidence that halogens play a spatially even wider role in the marine boundary layer and free troposphere for ozone destruction, changes in the ratios of OH/HO2 and NO/NO2, destruction of methane, in the oxidation of mercury and in the formation of secondary aerosol. There are indications that both, oceanic sources as well as the chemistry of halogens and volatile organic compounds (VOCs) and oxygenated VOCs (OVOCs) in the tropics are linked with potential implications not only for the photochemistry but also the formation of secondary organic aerosol (SOA). More recently, marine emissions of active halogens have been linked to potential impacts on oxidants loading in coastal cities. Finally, bromine and iodine are also being proposed as proxies of past sea ice variability.

We invite contributions in the following areas dealing with tropospheric halogens on local, regional, and global scales:

- Model studies: Investigations of the chemical mechanisms leading to release, transformation and removal of reactive halogen species in the troposphere. Studies of consequences of the presence of reactive halogen species in the troposphere.

- Laboratory studies: Determination of gas- and aqueous-phase rate constants, study of complex reaction systems involving halogens, Henry's law and uptake coefficients, UV/VIS spectra, and other properties of reactive halogen species.

- Field experiments and satellite studies: Measurements of inorganic (X, XO, HOX, XONO2, ..., X = Cl, Br, I) and organic (CH3Br, CHBr3, CH3I, RX, ...) reactive halogen species and their fluxes in the troposphere with in situ and remote sensing techniques.

- Measurements and model studies of the abundance of (reactive) halogen species in volcanic plumes and transformation processes and mechanisms.

- All aspects of tropical tropospheric halogens and links to (O)VOCs: their chemistry, sources and sinks, and their impact on local, regional, and global scales.

Methane is an important greenhouse gas that has contributed to ∼25% of the increase in radiative forcing experienced to date. Despite methane’s short atmospheric lifetime (~10 years), the global average methane mole fraction has increased three times faster than carbon dioxide since 1750. Rapid and severe reductions in methane emissions are required to lower peak warming, reduce the likelihood of overshooting warming limits and reduce reliance on net negative carbon dioxide emissions. In contrast to carbon dioxide, anthropogenic methane emissions originate from a large variety and number of sources including (but not limited to) oil and gas production, coal mining, fires, agriculture and waste.

A systematic and international effort on atmospheric measurements and emission quantification is needed to inform emission inventories and target mitigation strategies. This session will highlight measurement studies at all scales (from chambers to satellites) that focus on quantification of methane emissions from human activities. Particular emphasis is on studies that aim to (1) demonstrate accurate and repeatable methodologies for measurement of emissions (2) allow attribution of emissions to specific sources and (3) inform stakeholders on mitigation and policy pathways.

Volcanic aerosol clouds from major tropical eruptions cause periods of strong surface cooling in the historical climate record and are dominant influences within decadal surface temperature trends. Advancing our understanding of the influence of volcanoes on climate relies upon better knowledge of (i) the radiative forcings of past eruptions and the microphysical, chemical and dynamical processes which affect the evolution of stratospheric aerosol properties and (ii) the response mechanisms governing post-eruption climate variability and their dependency on the climate state at the time of the eruption. This can only be achieved by combining information from satellite and in-situ observations of recent eruptions, stratospheric aerosol and climate modelling activities, and reconstructions of past volcanic histories and post-eruption climate state from proxies.

In recent years the smoke from intense wildfires in North America and Australia has also been an important component of the stratospheric aerosol layer, the presence of organic aerosol and meteoric particles in background conditions now also firmly established.

This session seeks presentations from research aimed at better understanding the stratospheric aerosol layer, its volcanic perturbations and the associated impacts on climate through the post-industrial period (1750-present) and also those further back in the historical record. Observational and model studies on the 2022 eruption of Hunga Tonga are especially welcomed.

We also welcome contributions to understand the societal impacts of volcanic eruptions and the human responses to them. Contributions addressing volcanic influences on atmospheric composition, such as changes in stratospheric water vapour, ozone and other trace gases are also encouraged.

The session aims to bring together research contributing to several current international co-ordinated activities: SPARC-SSiRC, CMIP6-VolMIP, CMIP6-PMIP, and PAGES-VICS.

Atmospheric aerosol-cloud-climate interactions (e.g. heterogeneous nucleation, particle oxidation, photosensitization and the consequent emission of volatile organic compounds (VOCs),...) are fundamental processes in the atmosphere. Despite the importance of these processes in energy transfer, cloud dynamics, precipitation formation, and hence in climate change, little is known about the molecular mechanism and the respective contribution of different environmental conditions as well as the structural and chemical surface properties of the atmospheric aerosols. Ice particles in the atmosphere, both in cirrus and mixed-phase clouds, and the VOCs emitted to the atmosphere from cloud droplets, lakes, rivers, seas and oceans contribute to the largest uncertainty in interpretations of the Earth’s changing energy budget.
Fundamental understanding of the aerosol generation, emission and properties, and the associated heterogeneous ice nucleation has become a demand. To advance our knowledge about atmospheric processes, this session aims to bring together two research areas, namely (1) Atmospheric Surface-Science (A.S.S.) and (2) Ice Nucleating Particles (INP):

(1) A.S.S. is concerned with the experimental and theoretical approaches investigating atmospheric interactions (e.g. ice nucleation processes and photochemistry at water/air interface). The goal is to fill the gap between the large-scale atmospheric processes and gas-, water-, and ice- molecular level interactions.
(2) INP are concerned with the laboratory examination, on a fundamental level, trying to understand the nucleation processes and characterizing INP in the atmosphere.

Solicited Talk: "Photosensitization is in the air and impacts the multiphase on oxidation capacity", Christian George, Univ Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, F-69626, Villeurbanne, France.

We may point to the possibility to attend the Workshop on Bioaerosols and Ice Nucleation in Vienna, 22nd to 23rd April 2023. Details can be found here: https://www.tuwien.at/en/tch/pc/physical-chemistry-of-atmosphere/workshop
Please note the 13th International conference on carbonaceous particles in the atmosphere ICCPA (https://iccpa.lbl.gov), which takes place in summer this year in Berkeley, USA.

Cities are hotspots for the emissions of air pollutants and greenhouse gases from traffic, industry, household heating and energy production. Air pollution impacts are episodic and often exacerbated during heat waves, and greenhouse gases are often co-emitted with air pollutants. These relationships make cities both a major driver of climate change, and the locus of many harmful climate impacts. Urban air quality and the effect of policy measures are a challenge to monitor with traditional fixed stations or with models, because of the extreme variability in the cities’ geometry and emission patterns.

This session intends to bring together researchers of urban air quality and greenhouse gases. We invite submissions on topics related to urban air quality, heat stress, urban carbon budgets, and air pollution impacts including health. Topics may include sensor networks, personal monitoring, airborne observations, high spatial and temporal resolution model approaches, downscaling, source apportionment, isotopic source attribution methods, atmospheric processes, mechanisms for air quality deterioration, biogenic and anthropogenic precursors, allergens, community and personal exposure quantification, and air pollution effects.

The aim of this general session is to bring together the scientific community within air pollution modelling. The focus is ongoing research, new results and current problems related to the field of modelling the atmospheric transport and transformation of air pollutants and precursors on global, regional and local scales.

All presentations covering the research area of air pollution modelling are welcome, including recent model developments, applications and evaluations, physical and chemical parameterisations, process understanding, model testing, evaluation and uncertainty estimates, emissions, numerical methods, model systems and integration, forecasting, event-studies, scenarios, ensembles, assessment, etc.

The session focuses on the variability of the tropospheric and stratospheric chemical composition on the timescales from diurnal to decadal. It discusses the processes driving this variability and attribution of changes to specific drivers. Special emphasis is put on the value of high-quality long-term measurement data sets both from scientific and societal perspective and their sustainability. Supporting model simulations on different scales that utilize observational data will also be discussed. Contributions related to emerging constituents, new data sources and approached to atmospheric composition monitoring (e.g. low cost sensor, emerging measurement techniques), measurement campaign that addresses specific processes and long-term projections of the atmospheric chemical composition are also welcome in the session. The presentations that address policy-relevant datasets on atmospheric composition are cordially invited.
Researchers are invited to present novel scientific results from mid- and long-term observational time series from various programmes and networks such as the Global Atmosphere Watch (GAW) Programme, European Monitoring, and Evaluation Programme (EMEP), Network for the Detection of Atmospheric Composition Change (NDACC), Southern Hemisphere Additional Ozonesondes (SHADOZ), Advanced Global Atmospheric Gases Experiment (AGAGE), National Oceanic and Atmospheric Administration (NOAA), regular airborne (e.g. CARIBIC, IAGOS, CONTRAIL) and other campaigns as well as satellite data and model simulations. Data relevant to tropospheric and stratospheric composition, in particular, related to ozone depletion, climate change, and air quality as well as firn data on past atmospheric composition are welcome. We welcome contributions from multi-year modeling studies and inter-comparison exercises that address past and future tropospheric or stratospheric composition changes, carried out in the framework of international projects and initiatives.

Tropospheric ozone plays an important role in climate and air quality as a greenhouse gas and air pollutant with harmful impacts to human health, crops and ecosystems. This session will focus on studies that will facilitate ongoing assessments of ozone trends, examine trends in ozone precursor emissions and quantify the impacts of these trends on human health, vegetation and climate. We particularly welcome contributions in the following topic areas:
- Regional and global ozone trend analyses from surface, free troposphere and satellite observations
- Ozone trend attribution studies using ozone chemical precursor observations
- Impacts of tropospheric ozone pollution on human health, vegetation and climate
- Global and regional model studies of past and future ozone changes and their attribution
- Synthesis evaluations of relevant processes (deposition, stratosphere-troposphere exchange, radiative forcing, etc.)
- Comparative studies on urban ozone processes and evolution
- Harmonization and evaluation of ground based instruments for free tropospheric ozone measurements
- Chemical reanalysis
- Machine learning and data fusion approaches to enhance the quality and resolution of ozone analyses and forecasts

We welcome all abstracts that address the topics above and we especially encourage abstracts from members of the Tropospheric Ozone Assessment Report (TOAR) Phase II working groups.

Instrumentation and its development play a key role in advancing research, providing state-of-the-art tools to address scientific "open questions" and to enable novel fields of research leading to new discoveries.
Over the last several decades, atmospheric environmental monitoring has benefited from the development of novel spectroscopic measurement techniques owing to the significant breakthroughs in photonic technology from the UV to Microwave spectral regions. These advances open new research avenues for observation of spatial and long-term trends in key atmospheric precursors, thus improving our understanding of tropospheric chemical processes and trends that affect regional air quality and global climate change. Extensive development of spectroscopic instruments for sensing the atmosphere continues toward improving performance and functionality, and reducing size and cost.
This focus session addresses the latest developments and advances in a broad range of spectroscopic instrumentation and photonic/optoelectronic devices and technologies, and their integration for a variety of atmospheric applications. The objective is to provide a platform for sharing information on state-of-the-art and emerging developments in photonic instrumentation for atmospheric sensing. This interdis¬ciplinary forum aims to foster discussion among experimentalists, atmospheric scientists, and development engineers. It is also an opportunity for R&D and analytical equipment companies to evaluate the capabilities of new instrumentation and techniques.
Topics for presentation include novel spectroscopic methods and instruments for measuring atmospheric aerosols, isotopologues, trace gases and radicals. In situ and remote observations, vertical concentration profiles, and flux measurements are all welcome. Spectroscopic methods could include high performance absorption spectroscopy (such as Dual Comb Spectroscopy, broadband and laser-based cavity-enhanced spectroscopies and multipass systems, and other high-sensitivity spectroscopic methods), fluorescence techniques, heterodyne radiometry, and aerosol spectroscopy. Applications and novel demonstrations including field observations, airborne platforms (UAV, balloon, aircraft), geological exploration, and smog chamber studies are welcome. Creative approaches using new photonic technologies, methodologies, and data analysis tools are particularly encouraged.

Over the last years, more and more satellite data on tropospheric composition have become available and are now being used in numerous applications. In this session, we aim at bringing together reports on new or improved data products and their validation as well as studies using satellite data for applications in tropospheric chemistry, emission inversions and air quality. This includes both studies on trace gases and on aerosols.

We welcome presentations based on studies analysing current and future satellite missions, in particular Sentinel 5P and GEMS, inter-comparisons of different remote sensing measurements dedicated to tropospheric chemistry sounding and/or analyses with ground-based measurements and chemical transport models.

Accurate and precise, long-term atmospheric measurements of greenhouse gas (GHG) concentrations reveal the rapid and unceasing rise of global GHG concentrations due to human activity. The resulting increases in global temperatures, sea-level, glacial retreat, and other negative impacts are clear. In response to this evidence, nations, states, and cities, industries and individuals have been accelerating GHG emission reduction and other mitigation efforts while working towards equitable development and environmental justice. The urgency, complexity, and economic implications of the needed GHG emission reductions and other climate action demand strategic investment in science-based information for planning and tracking emission reduction policies and actions. An example of an intergovernmental response can be seen in the World Meteorological Organization’s (WMO) Integrated Global Greenhouse Gas Information System (IG3IS). The IG3IS initiative seeks to enhance the capacity of nations, states, cities, and industries to target emissions reduction opportunities and track progress towards their goals. Success depends on infrastructure investments and the availability of measurements of atmospheric composition and emission activity data in key GHG emission source regions and relies on a multi-tiered observing strategy involving satellite, aircraft, and surface-based measurements, as well as innovative data mining and analysis methods. Such science-based services also depend on successful analysis methods and mature use-cases for which the scientific and technical skill is proven or emerging.

This session intends to gather presentations from researchers, inventory compilers, information service providers, as well as decision-maker and policy user-community. The session seeks presentations of work focused on the development, implementation, use and impact of measurement-based “top-down,” activity data-driven “bottom-up,” and the hybrid combinations of both approaches for GHG monitoring and improved emission inventory estimates that deliver actionable GHG information from granular space and time scales of explicit emission activity where climate action is achievable up to the global scale in support of Paris agreement stocktake.

Observations from aircraft, remotely piloted aircraft systems (RPAS/UAV/UAS) and balloons are an important means to obtain a broad view of processes within the Earth environment during measurement campaigns. The range of available instruments enables a broad and flexible range of applications. It includes sensors for meteorological parameters, trace gases and cloud/aerosol particles and more complex systems like high spectral resolution lidar, hyperspectral imaging at wavelengths from the visible to thermal infra-red, solar-induced fluorescence and synthetic aperture radar. The use of small state-of-the-art instruments, the combination of more and more complex sets of instruments with improved accuracy and data acquisition speed enables more complex campaign strategies even on small aircraft, balloons or RPAS.
Applications include atmospheric parameters, structural and functional properties of vegetation, glaciological processes, sea ice and iceberg studies, soil and minerals and dissolved or suspended matter in inland water and the ocean. Ground based systems and satellites are key information sources to complement airborne datasets and a comprehensive view of the observed system is often obtained by combining all three. Aircraft and balloon operations depend on weather conditions either to obtain the atmospheric phenomenon of interest or the required surface-viewing conditions and so require detailed planning. They provide large horizontal and vertical coverage with adaptable temporal sampling. Future satellite instruments can be tested using airborne platforms during their development. The validation of operational satellite systems and applications using airborne measurements has come increasingly into focus with the European Copernicus program in recent years.
This session will bring together aircraft, balloon and RPAS operators and researchers to present:
• an overview of the current status of environmental research focusing on the use of airborne platforms
• recent observation campaigns and their outcomes
• multi-aircraft/balloon/RPAS and multi-RI campaigns
• using airborne and ground-based RI to complement satellite data, including cal/val campaigns
• identifying and closing capability gaps
• contributions of airborne measurements to modelling activities
• airborne platforms to reduce the environmental footprint of alternative observation strategies
• airborne instruments, developments and observations
• future plans involving airborne research

As part of this session we invite contributions from the field and laboratory experiments and the very latest instrument developments as well as theoretical and modeling activities that advance our understanding of biogeochemical and atmospheric processes using stable isotopes of light elements (C, H, O, N) as well as other novel tracers (such as carbonyl sulfide (COS)), for example:

- Stable isotopes in carbon dioxide (CO2), water (H2O), methane (CH4), carbonyl sulfide (COS), and nitrous oxide (N2O)

- Novel tracers and biological analogues, such as carbonyl sulfide (COS)

- Polyisotopocules ("clumped isotopes")

- Intramolecular stable isotope distributions ("isotopomer abundances")

- Analytical, method and modeling developments

- Flux measurements

- Quantification of isotope effects

- Non-mass-dependent isotopic fractionation and related isotope anomalies

The nonlinear nature of fluid flow gives rise to a wealth of interesting and beautiful phenomena. Many of these are of fundamental importance in the understanding of lakes, oceans and the atmosphere because of their role in such things as transport, the energy cascade and, ultimately, in mixing. This session is intended to bring together researchers interested in the fundamental nature of nonlinear processes in rivers, lakes, oceans and the atmosphere. Examples include, but are not limited to, nonlinear and solitary waves, wave-current and wave-wave interactions, flow instabilities and their nonlinear evolution, turbulence, frontogenesis, double diffusion and the nonlinear equation of state, convection, and river plumes. Presentations on theoretical, modelling, experimental or observational work are welcome.

Atmosphere and Cryosphere are closely linked and need to be investigated as an interdisciplinary subject. Most of the cryospheric areas have undergone severe changes in last decades while such areas have been more fragile and less adaptable to global climate changes. This AS-CR session invites model- and observational-based investigations on any aspects of linkages between atmospheric processes and snow and ice on local, regional and global scales. Emphasis is given on the Arctic and Antarctic regions, high latitudes and altitudes, mountains, sea ice and permafrost regions. In particular, we encourage studies that address aerosols (such as Black Carbon, Organic Carbon, dust, volcanic ash, microplastics, pollen, sea salt, diatoms, bioaerosols, bacteria, etc.) and changes in the cryosphere, e.g., effects on snow/ice melt and albedo. The session also focuses on dust transport, aeolian deposition, and volcanic dust, including health, environmental or climate impacts at high latitudes, high altitudes and cold Polar Regions. We include contributions on biological and ecological sciences including dust-organisms interactions, cryoconites, bio-albedo, eco-physiological, biogeochemical and genomic studies. Related topics are light absorbing impurities, cold deserts, dust storms, long-range transport, glaciers darkening, polar ecology, and more. The scientific understanding of the AS-CR interaction needs to be addressed better and linked to the global climate predictions scenarios.

The Aviation Meteorology And Nowcasting: Observations and Models (AMANOM) session
will focus on observations and NWP model applications related to fog, clouds, contrails, icing and precipitation, and short-range forecasting of weather conditions associated with aviation operations. Abstracts for all areas of aviation meteorology, including Polar region, high altitude conditions, as well as airport environments, can be submitted to this session. Work on aviation meteorology parameters such as visibility, icing, gusts and turbulence, as well as fog and precipitation, will be considered for this session. Topics related to In-situ observations obtained from aircraft, Uncrewed Aerial Vehicles (UAVs), Tethered Balloon Systems (TBS), and supersites, remote sensing retrievals of meteorological parameters from satellites, radars, lidars, and MicroWave Radiometers (MWRs), as well as other emerging technological platforms, and predictions of meteorological parameters from the numerical weather prediction models will be considered highly related to the goals of this session.

Fire is an essential feature of many ecosystems and an important component of the Earth system. Climate, vegetation, and human activity regulate fire occurrence and spread, but fires also feedback to them in multiple ways, resulting in changing fire regimes in many regions of the world. This session welcomes contributions that explore the role of fire in the Earth system at any temporal and spatial scale using modeling, field and laboratory observations, proxy-records including tree fire scars, sedimentary charcoal cores, ice cores, speleothems, and/or remote sensing. We encourage abstracts that advance our understanding on (1) fire related emissions (e.g. emission factors, emission height, smoke transport), (2) spatial and temporal changes of fire regimes in the past, present, and future, (3) fire products and models, and their validation, error/bias assessment and correction, (4) analytical tools designed to enhance situational awareness among fire practitioners and early warning systems. We are also welcoming submissions on fire related changes (5) in weather, climate, as well as atmospheric chemistry and circulation, (6) vegetation composition and structure, (7) cryosphere (e.g. permafrost, sea ice), (2) biogeochemical cycling of carbon, nitrogen and trace elements, (8) soil functioning and soil organic matter dynamics, as well as (9) effects of fires on humans (e.g., impact of fire on air and water quality, freshwater resources, human health, land use and land cover change, fire management).

Early career researchers and underrepresented groups in the field are strongly encouraged to apply.

A correct characterization of atmospheric transport and deposition is crucial for the understanding of environmental challenges such as air quality problems and climate change. The deposition of atmospheric pollutants represents a major threat for terrestrial ecosystem integrity and biodiversity. The impacts of the recent large wildfires, the distribution of microplastic particles and biological material such as pollen as well as the input of nutrients and acidifying compounds, such as reactive nitrogen, and of other pollutants to ecosystems are linked to both atmospheric transport and deposition.

Yet, considerable uncertainties in the correct representation of atmospheric transport and deposition processes exist. These uncertainties also affect nature protection policies as well as emission regulation and mitigation strategies.

This session spans from the transport of atmospheric pollutants from local to global scales to their deposition on terrestrial ecosystems, including:
• Studies combining observations and models to infer information about emissions, transport and deposition characteristics.
• In particular, studies aimed at improving the understanding and quantification of dry, wet and occult deposition processes by the use of experimental approaches, using e.g. micrometeorological methods or deposition samplers, and process based and large-scale deposition modelling and the combinations thereof.
• New developments in atmospheric transport modelling, including the improvement of parameterization of atmospheric processes, the quantitative assessment of uncertainties, improving model performance, and the proper coupling of Lagrangian models to Eulerian Numerical Weather Prediction and General Circulation models.

The field of infrasonic research, the science of low-frequency acoustic waves, has expanded to include acoustic-gravity waves and developed into a broad interdisciplinary field encompassing academic disciplines of geophysics and recent technical and basic scientific developments. The International Monitoring System (IMS) infrasound network for nuclear test ban verification and regional infrasound arrays deployed around the globe have demonstrated their capacity for detecting and locating various natural and anthropogenic disturbances in the atmosphere. Infrasound and acoustic-gravity waves are capable of traveling up to thermospheric altitudes and over enormous ranges, where the wind and temperature structure controls their propagation. Recent studies have offered new insights on quantitative relationships between infrasonic observations and atmospheric dynamics, and therefore open a new field for atmospheric remote sensing.

New studies using lidar, radar, microwave spectrometer, and mesospheric airglow observations complemented by satellite measurements help better determine the interaction between atmospheric layers from the ground to the mesosphere and the influence of atmospheric waves on the mean flow. It is expected that further developing multi-instruments platforms would improve gravity wave parameterizations and enlarge the science community interested in operational infrasound monitoring. In a higher frequency range, the infrasound monitoring system also offers a unique opportunity to provide, in near-real time, continuous relevant information about natural hazards with high societal impact, such as large volcanic eruptions, surface earthquakes, meteoroids, and bright fireballs.

We invite contributions on recent studies characterizing infrasound sources or large-scale atmospheric phenomena, including presentations utilizing acoustic waves to probe the atmosphere. Results and advances in acoustic propagation modeling and innovative instrumentation, which also encompasses the extension of regional array networks, are welcome. We also invite studies of the role that infrasound and acoustic-gravity waves play in the coupled Earth’s crust – ocean – atmosphere system and, in particular, in ionospheric manifestations of physical processes in the ocean and in the solid Earth. Contributions highlighting data products and services for civilian and scientific applications utilizing or supplementing infrasound observations are particularly encouraged.

Cosmic rays carry information about space and solar activity, and, once near the Earth, they produce isotopes, influence genetic information, and are extraordinarily sensitive to water. Given the vast spectrum of interactions of cosmic rays with matter in different parts of the Earth and other planets, cosmic-ray research ranges from studies of the solar system to the history of the Earth, and from health and security issues to hydrology, agriculture, and climate change.
Although research on cosmic-ray particles is connected to a variety of disciplines and applications, they all share similar questions and challenges regarding the physics of detection, modeling, and the influence of environmental factors.

The session brings together scientists from all fields of research that are related to monitoring and modeling of cosmogenic radiation. It will allow sharing of expertise amongst international researchers as well as showcase recent advancements in their field. The session aims to stimulate discussions about how individual disciplines can share their knowledge and benefit from each other.

We solicit contributions related but not limited to:
- Health, security, and radiation protection: cosmic-ray dosimetry on Earth and its dependence on environmental and atmospheric factors
- Planetary space science: satellite and ground-based neutron and gamma-ray sensors to detect water and soil constituents
- Neutron and Muon monitors: detection of high-energy cosmic-ray variations and its dependence on local, atmospheric, and magnetospheric factors
- Hydrology and climate change: low-energy neutron sensing to measure water in reservoirs at and near the land surface, such as soils, snow pack, and vegetation
- Cosmogenic nuclides: as tracers of atmospheric circulation and mixing; as a tool in archaeology or glaciology for dating of ice and measuring ablation rates; and as a tool for surface exposure dating and measuring rates of surficial geological processes
- Detector design: technological advancements in the detection of cosmic rays and cosmogenic particles
- Cosmic-ray modeling: advances in modeling of the cosmic-ray propagation through the magnetosphere and atmosphere, and their response to the Earth's surface
- Impact modeling: How can cosmic-ray monitoring support environmental models, weather and climate forecasting, agricultural and irrigation management, and the assessment of natural hazards

Wind and solar power are the predominant new sources of electrical power in recent years. Several countries or regions regularly exceed 100% of variable renewable energy in their grids. By their very nature, wind and solar power, as well as hydro, tidal, wave and other renewable forms of generation are dependent on weather and climate. Modelling and measurement for resource assessment, site selection, long-term and short term variability analysis and operational forecasting for horizons ranging from minutes to decades are of paramount importance.

The success of wind power means that wind turbines are increasingly put in sites with complex terrain or forests, with towers extending beyond the strict logarithmic profile, and in offshore regions that are difficult to model and measure. Major challenges for solar power are notably accurate measurements and the short-term prediction of the spatiotemporal evolution of the effects of cloud field and aerosols. Planning and meteorology challenges in Smart Cities are common for both.

The integration of large amounts of renewable energy into the grid is another critical research problem due to the uncertainties linked to their forecast and to patterns of their spatio-temporal variabilities.

We invite contributions on all aspects of weather dependent renewable power generation, e.g.:

• Wind conditions (both resources, siting conditions and loads) on short and long time scales for wind power development, especially in complex environments (e.g. mountains, forests, coastal or urban).
• Long term analysis of inter-annual variability of solar and wind resource
• Typical Meteorological Year and probability of exceedance for wind and solar power development,
• Wind and solar resource and atlases.
• Wake effect models and measurements, especially for large wind farms and offshore.
• Performance and uncertainties of forecasts of renewable power at different time horizons and in different external conditions.
• Forecast of extreme wind events and wind ramps.
• Local, regional and global impacts of renewable energy power plants or of large-scale integration.
• Dedicated wind measurement techniques (SODARS, LIDARS, UAVs etc.).
• Dedicated solar measurement techniques (pyranometric sensors, sun-photometer, ceilometer, fish-eye cameras, etc.) from ground-based and space-borne remote sensing.
• Tools for urban area renewable energy supply strategic planning and control.
Other related topics will be considered by the conveners.

Volcanoes release gas effluents and aerosol particles into the atmosphere during eruptive episodes and by quiescent emissions. Volcanic degassing exerts a dominant role in forcing the timing and nature of volcanic unrest and eruptions. Understanding the exsolution processes of gas species dissolved in magma, and measuring their emissions is crucial to characterise eruptive mechanism and evaluate the sub-sequent impacts on the atmospheric composition, the environment and the biosphere. Emissions range from silent exhalation through soils to astonishing eruptive clouds that release gas and particles into the atmosphere, potentially exerting a strong impact on the Earth’s radiation budget and climate over a range of temporal and spatial scales. Strong explosive volcanic eruptions are a major natural driver of climate variability at interannual to multidecadal time scales. Quiescent passive degassing and smaller-magnitude eruptions on the other hand can impact on regional climate system. Through direct exposure and indirect effects, volcanic emissions may influence local-to-regional air quality and seriously affect the biosphere and environment. Volcanic gases can also present significant hazards to populations downwind of an eruption, in terms of human, animal and plant health, which subsequently can affect livelihoods and cause socio-economic challenges. Gas emissions are measured and monitored via a range of in-situ and remote sensing techniques, to gain insights into both the subterranean-surface processes and quantify the extent of their impacts. In addition, modelling of the subsurface and atmospheric/climatic processes, as well as laboratory experiments, are fundamental to the interpretation of field-based and satellite observations.

This session focuses on the state-of-the-art and interdisciplinary science concerning all aspects of volcanic degassing and impacts of relevance to the Volcanology, Environmental, Atmospheric and Climate sciences (including regional climate), and Hazard assessment. We invite contributions on all aspects of volcanic plumes science, their observation, modelling and impacts. We welcome contributions that address issues around the assessment of hazards and impacts from volcanic degassing both in crises and at persistently degassing volcanoes.

The heliosphere is permeated with energetic particles of different compositions, energy spectra and origins. Two major populations of these particles are galactic cosmic rays (GCRs), which originate from outside of the heliosphere and are constantly detected at Earth, and solar energetic particles (SEPs) which are accelerated at/near the Sun during solar flares or by shock fronts associated with the transit of coronal mass ejections. Enhancements in energetic particle fluxes at Earth pose a hazard to humans and technology in space and at high altitudes. Within the magnetosphere, energetic particles are present in the radiation belts, and particle precipitation is responsible for the aurora and for hazards to satellites. Energetic particles have also been shown to cause changes is the chemistry of the middle and upper atmosphere, thermodynamic effects in the upper troposphere and lower stratosphere region, and can influence components of the global electric circuit. This session will aim to address the transport of energetic particles through the heliosphere, their detection at Earth and the effects they have on the terrestrial atmosphere when they arrive. It will bring together scientists from several fields of research in what is now very much an interdisciplinary area. The session will allow sharing of expertise amongst international researchers as well as showcase the recent advances being made in this field, which demonstrate the importance of the study of these energetic particle populations.

Machine learning (ML) is currently transforming data analysis and modelling of the Earth system. While statistical and data-driven models have been used for a long time, recent advances in machine learning now allow for encoding non-linear, spatio-temporal relationships robustly without sacrificing interpretability. This has the potential to accelerate climate science, by providing new physics-based modelling approaches; improving our understanding of the underlying processes; reducing and better quantifying climate signals, variability, and uncertainty; and even making predictions directly from observations across different spatio-temporal scales. The limitations of machine learning methods need to also be considered, such as requiring, in general, rather large training datasets, data leakage, and/or poor generalisation abilities, so that methods are applied where they are fit for purpose and add value.

This session aims to provide a venue to present the latest progress in the use of ML applied to all aspects of climate science and we welcome abstracts focussed on, but not limited to:
- Causal discovery and inference: causal impact assessment, interventions, counterfactual analysis
- Learning (causal) process and feature representations in observations or across models and observations
- Hybrid models (physically informed ML, emulation, data-model integration)
- Novel detection and attribution approaches
- Probabilistic modelling and uncertainty quantification
- Explainable AI applications to climate data science and climate modelling
- Distributional robustness, transfer learning and/or out-of-distribution generalisation tasks in climate science

Please note that a companion session “ML for Earth System modelling” focuses specifically on ML for model improvement, particularly for near-term time-scales (including seasonal and decadal) forecasting, and related abstracts should be submitted there.

Unsupervised, supervised, semi-supervised as well as reinforcement learning are now increasingly used to address Earth system-related challenges for the atmosphere, the ocean, the land surface, or the sea ice.
Machine learning could help extract information from numerous Earth System data, such as in-situ and satellite observations, as well as improve model prediction through novel parameterizations or speed-ups. This session invites submissions spanning modeling and observational approaches towards providing an overview of state-of-the-art applications of these novel methods for predicting and monitoring the Earth System from short to decadal time scales. This includes (but is not restricted to):
- The use of machine learning to reduce or estimate model uncertainty
- Generate significant speedups
- Design new parameterization schemes
- Emulate numerical models
- Fundamental process understanding

Please consider submitting abstracts focused on ML applied to observations and modeling of the climate and its constituent processes to the companion "ML for Climate Science" session.

In weather prediction and climate modelling, numerical models of the Earth System are used extensively. For both the atmosphere and ocean components such models consist of a fluid dynamics solver (dynamical core) coupled to physical parameterizations to represent processes that occur below the grid scale (physics). Over time these models have become capable of sophisticated simulations. Research and development is constantly being undertaken to improve the accuracy, efficiency, and scalability of the dynamical core, the physics, and their coupling.

This session encompasses the development, testing and application of novel numerical techniques for Earth system models, including governing equations, horizontal and vertical discretizations, structure preserving methods, time stepping schemes (including parallel in time schemes), advection schemes, adaptive multi-scale models, physics-dynamics coupling, regional and global models, classical and stochastic physical parameterizations.

Inverse Problems are encountered in many fields of geosciences. One class of inverse problems, in the context of predictability, is assimilation of observations in dynamical models of the system under study. Furthermore, objective quantification of the uncertainty during data assimilation, prediction and validation is the object of growing concern and interest.
This session will be devoted to the presentation and discussion of methods for inverse problems, data assimilation and associated uncertainty quantification throughout the Earth System like in ocean and atmosphere dynamics, atmospheric chemistry, hydrology, climate science, solid earth geophysics and, more generally, in all fields of geosciences.
We encourage presentations on advanced methods, and related mathematical developments, suitable for situations in which local linear and Gaussian hypotheses are not valid and/or for situations in which significant model or observation errors are present. Specific problems arise in situations where coupling is present between different components of the Earth system, which gives rise to the so called coupled data assimilation.
Of interest are also contributions on weakly and strongly coupled data assimilation - methodology and applications, including Numerical Prediction, Environmental forecasts, Earth system monitoring, reanalysis, etc., as well as coupled covariances and the added value of observations at the interfaces of coupled models.
We also welcome contributions dealing with algorithmic aspects and numerical implementation of the solution of inverse problems and quantification of the associated uncertainty, as well as novel methodologies at the crossroad between data assimilation and purely data-driven, machine-learning-type algorithms.

Downscaling aims to process and refine global climate model output to provide information at spatial and temporal scales suitable for impact studies. In response to the current challenges posed by climate change and variability, downscaling techniques continue to play an important role in the development of user-driven climate information and new climate services and products. In fact, the "user's dilemma" is no longer that there is a lack of downscaled data, but rather how to select amongst the available datasets and to assess their credibility. In this context, model evaluation and verification is growing in relevance and advances in the field will likely require close collaboration between various disciplines.

Furthermore, epistemologists have started to revisit current practices of climate model validation. This new thread of discussion encourages to clarify the issue of added value of downscaling, i.e. the value gained through adding another level of complexity to the uncertainty cascade. For example, the ‘adequacy-for-purpose view’ may offer a more holistic approach to the evaluation of downscaling models (and atmospheric models, in general) as it considers, for example, user perspectives next to a model’s representational accuracy.

In our session, we aim to bring together scientists from the various geoscientific disciplines interrelated through downscaling: atmospheric modeling, climate change impact modeling, machine learning and verification research. We also invite philosophers of climate science to enrich our discussion about novel challenges faced by the evaluation of increasingly complex simulation models.

Contributions to this session may address, but are not limited to:

- newly available downscaling products,
- applications relying on downscaled data,
- downscaling method development, including the potential for machine learning,
- bias correction and statistical postprocessing,
- challenges in the data management of kilometer-scale simulations,
- verification, uncertainty quantification and the added value of downscaling,
- downscaling approaches in light of computational epistemology.

This session invites contributions on the latest developments and results in lidar remote sensing of the atmosphere, covering • new lidar techniques as well as applications of lidar data for model verification and assimilation, • ground-based, airborne, and space-borne lidar systems, • unique research systems as well as networks of instruments, • lidar observations of aerosols and clouds, thermodynamic parameters and wind, and trace-gases. Atmospheric lidar technologies have shown significant progress in recent years. While, some years ago, there were only a few research systems, mostly quite complex and difficult to operate on a longer-term basis because a team of experts was continuously required for their operation, advancements in laser transmitter and receiver technologies have resulted in much more rugged systems nowadays, many of which are already operated routinely in networks and several even being fully automated and commercially available. Consequently, also more and more data sets with very high resolution in range and time are becoming available for atmospheric science, which makes it attractive to consider lidar data not only for case studies but also for extended model comparison statistics and data assimilation. Here, ceilometers provide not only information on the cloud bottom height but also profiles of aerosol and cloud backscatter signals. Scanning Doppler lidars extend the data to horizontal and vertical wind profiles. Raman lidars and high-spectral resolution lidars provide more details than ceilometers and measure particle extinction and backscatter coefficients at multiple wavelengths. Other Raman lidars measure water vapor mixing ratio and temperature profiles. Differential absorption lidars give profiles of absolute humidity or other trace gases (like ozone, NOx, SO2, CO2, methane etc.). Depolarization lidars provide information on the shapes of aerosol and cloud particles. In addition to instruments on the ground, lidars are operated from airborne platforms in different altitudes. Even the first space-borne missions are now in orbit while more are currently in preparation. All these aspects of lidar remote sensing in the atmosphere will be part of this session.

Remote sensing of clouds and aerosols is of central importance for studying climate system processes and changes. Reliable information is required on climate-relevant parameters such as aerosol and cloud optical thickness, layer height, particle size, liquid or ice water path and vertical particulate matter columns. A number of challenges and unsolved problems remain in algorithms and their application. This includes remote sensing of clouds and aerosols with respect to 3D effects, remote sensing of polluted and mixed clouds, combination of ground-based and satellite-based systems, and the creation of long-term uniform global records. This session is aimed at the discussion of current developments, challenges and opportunities in aerosol and cloud remote sensing using active and passive remote sensing systems.

Understanding the physical and chemical processes that take place in the atmosphere benefits from observations of its dynamics and composition in a variety of conditions and situations. To accomplish this, scientists employ instrumentation for in situ and remotely sensed quantities from a variety of ground, airborne, and space-based platforms. In 2022, several observational field campaigns related to tropospheric composition and dynamics in urban and suburban environments were conducted throughout the globe, and especially during the summer in Paris under the framework of the PANAME (PAris region urbaN Atmospheric observations and models for Multidisciplinary rEsearch) 2022 initiative. While these projects had a variety of specific goals, some of them were designed to examine aspects of the evolution of urban and rural air masses as they are transported from cities to the surrounding peri-urban, suburban, and rural areas. Such studies complement investigations of strictly urban or rural environments including air quality and its link with urban or suburban vegetation, urban meteorology, cities and climate change, and climate in cities and the link with human activities and health. Some of these projects also specifically examine aspects of the evolution of urban air masses as they are transported from cities to the surrounding peri urban, suburban, and rural areas.

Presentations in this session will describe measurements performed during the 2022 campaigns in Paris region and other megacities measurements of quantities observed during the 2022 campaign season, while providing initial and first analyses of the observations including employing numerical models. The primary goal of the session is to identify findings related to new or poorly understood chemical and physical processes associated with emission, transport, and transformation of substances in megacities and within the framework of transitions from urban-to-rural environments, as well as new insights into urban-suburban meteorology and dynamics.

The Quaternary Period (last 2.6 million years) is characterized by frequent and abrupt climate swings that were accompanied by rapid environmental change. Studying these changes requires accurate and precise dating methods that can be effectively applied to environmental archives. A range of different methods or a combination of various dating techniques can be used, depending on the archive, time range, and research question.
Radiocarbon (14C) in particular is a key environmental tracer that can be widely applied in geochronology, environmental, and climate sciences. It is an invaluable tool to understand the global carbon cycle, as it can be used to trace the transfer of carbon between the atmosphere and other reservoirs, e.g., soils, oceans, and the geosphere, and to understand the impact of anthropogenic perturbations on these reservoirs.

With this session, we aim at bringing together an interdisciplinary group of researchers focused on dating and understanding climate archives of the Quaternary Period. Our session will focus on the application of geochronometers on one hand, as well as on the use of radiocarbon from natural reservoirs and archives that improve our understanding of the carbon cycle. In particular, we look forward to discussing (1) experimental and analytical advances (e.g. in sample preparation and measurement techniques); (2) methods that reduce, quantify and express dating uncertainties in any dating method, including high-resolution radiocarbon approaches; (3) new insights into the global carbon cycle, e.g., storage times in soils, sediment dispersal, ocean circulation, or carbon transfer between reservoirs; (4) general geochronological applications such as long-term landscape evolution, rates of geomorphological processes, and chronologies for records of climate change.

Geodesy contributes to atmospheric science by providing some of the essential climate variables of the Global Climate Observing System. Water Vapor (WV) is currently under-sampled in meteorological and climate observing systems. Obtaining more high-quality humidity observations is essential to weather forecasting and climate monitoring. The production, exploitation and evaluation of operational GNSS-Met for weather forecasting is well established in Europe due to 20+ years of cooperation between the geodetic community and the national meteorological services. Improving the skill of numerical weather prediction (NWP) models to forecast extreme precipitation requires GNSS products with a higher spatio-temporal resolution and shorter turnaround. Homogeneously reprocessed GNSS data (e.g., IGS repro3) have high potential for monitoring water vapor climatic trends and variability. With shortening orbit repeat periods, SAR measurements are a new source of information to improve NWP models. Using NWP data within real-time (RT) GNSS data analysis can initialize PPP algorithms, thus shortening convergence times and improving positioning. GNSS signals can be used for L-band remote sensing when Earth-surface reflected signals are considered. GNSS-R contributes to environmental monitoring with estimates of soil moisture, snow depth, ocean wind speed, sea ice concentration and has the potential to be used to retrieve near-surface WV.
We welcome, but not limit, contributions on:
•Estimates of the neutral atmosphere using ground- and space-based geodetic data and the use thereof in weather forecasting and climate monitoring
•Retrieval and comparison of tropospheric parameters from multi-GNSS, VLBI, DORIS and multi-sensor observations
•Now-casting, forecasting, and climate research using RT and reprocessed tropospheric products, employing numerical weather prediction and machine learning
•Assimilation of GNSS tropospheric products in NWP and in climate reanalysis
•Production of SAR tropospheric parameters and assimilation thereof in NWP
•Homogenization of long-term GNSS and VLBI tropospheric products
•Delay properties of GNSS signals for propagation experiments
•Exploitation of NWP data in GNSS data processing
•Techniques for soil moisture retrieval from GNSS data and for ground-atmosphere boundary interactions
•Detection and characterization of sea level, snow depth and sea ice changes, using GNSS-R
•Studying the atmospheric water cycle employing satellite gravimetry.

Air pollution is a leading environmental risk factor for people living in Africa and South/Southeast Asia. These regions have diverse sources of air pollution (e.g., industrial, domestic burning, biomass burning, traffic, etc.) and atmospheric processes that influence the pollution loadings (e.g., boundary layer dynamics, long-range transport, secondary air pollution, etc.). Air quality management in data scarce regions with high temporal and spatial diversity in air pollution sources and atmospheric processes poses complex challenges. While the air quality may vary greatly within and between Africa and South/Southeast Asia, the need for evidence-based approaches for improving air quality with limited data are common.

This session will bring together participants working on measurement- and/or modeling-based approaches for air quality applications in Africa and South/Southeast Asia. These applications can range from emission inventories, chemical transport modeling, chemical analysis, source apportionment, regulatory and hybrid monitoring, air quality forecasting, scenario analysis, health impacts, and other policy applications at urban, rural, national, and regional scales. We expect the participants to engage meaningfully and critically with at least one practical application of their analysis in the context of science, technology, policy, citizen engagement, capacity building, or institutional development. We also expect the participants to think about the interlinkages (or lack thereof) of their work in a broader context within and between Africa and South/Southeast Asia as they relate to aspects such as knowledge exchange/sharing, data sharing, data management, analytical techniques, or other evidence-based approaches to air quality management.

We can support up to 20 participants who are based in Africa or South/Southeast Asia with travel awards of 3000 Euros each to attend this session in Vienna. Please send a short cover letter (up to 200 words) to the convener after you have submitted your abstract to be considered for the travel award. Awardees will be selected by the (co-)conveners based on their abstract and cover letter. We acknowledge Open Philanthropy for this funding and the University of Helsinki for managing the travel awards.