This session welcomes papers on:

1) Forecasting and simulating high impact weather events - research on using advanced artificial intelligence and machine learning techniques to improve numerical weather model prediction of severe weather events (such as winter storms, tropical storms, and severe mesoscale convective storms);

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) Verification of model physics and forecast products against theories and observations;

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 applying data from various conventional and avant-garde observation platforms to evaluate and improve high-resolution simulations and forecasting.

8) Application of Artificial Intelligence / Machine Learning in weather forecasting in general

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
 Remote sensing and data assimilation
 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.

Key Words: Forecast technique, nowcasting, ensemble prediction, statistics, AI

This session invites contributions spanning all aspects of prediction, predictability and applications on the Subseasonal-to-Seasonal (S2S) (i.e., 2 weeks to 2 months) lead time range. The session welcomes contributions on the following:

(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) Use of AI/ML methods for S2S prediction, post-processing and attribution;
(g) Case studies of extreme or high-impact event prediction on the S2S timescale; and
(h) User applications, impact studies and climate services on the S2S timescale including, including impact-focused modelling studies and examples of how S2S-derived information can be integrated into decision support systems at the local, regional or international level.

This session covers climate predictions from seasonal to multi-decadal timescales and their applications. Continuing to improve such predictions is of major importance to society. The session embraces advances in our understanding of the origins of seasonal to decadal predictability and of the limitations of such predictions, as well as advances in improving the forecast skill and reliability 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 and natural hazards, 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 innovative ensemble-forecast initialization and generation strategies 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 assessing risks from natural hazards, adaptation and further applications.

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.

Understanding severe convection and associated hazardous weather is crucial to mitigate societal impacts now and in a warmer future. However, convective-scale data analysis and severe weather predictions still present significant challenges for atmospheric sciences. Addressing these challenges requires a synergy of high-resolution convection-permitting modelling, observations, and data assimilation advances. For this reason, our session connects recent advancements in convective-scale process modelling, process understanding, data assimilation, prediction, observing systems, and machine learning.

Session objectives:
• To improve the process understanding and modelling of mesoscale and severe convection in current and future climates.
• To improve convective-scale data assimilation, forecasting and observation methodologies.
• To provide a collaborative platform for enhancing the predictability, uncertainty quantification and understanding of severe weather events and their impacts.
• To bridge mesoscale convective studies with novel convective-scale data assimilation and modelling techniques.

Key Topics:
• Dynamics, thermodynamics and microphysics of mesoscale and severe convection on weather and climate timescales.
• Impact of land-convection interactions, considering environmental factors like complex topography, soil moisture feedbacks,or land use (change).
• Advances in convective-scale data assimilation, forecasting and observations.
• Advances in machine learning for improved modelling of convective-scale processes.

The uncertain response of clouds to global warming is a major contributor to uncertainty in climate sensitivity. 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. Today's wealth of advanced remote-sensing observations and high-resolution modelling data provides comprehensive and complementary information that enables detailed process and lifecycle-based analyses. This session focuses on (1) efforts to advance our understanding of the cloud-circulation coupling and its role in climate change, and (2) Lagrangian studies related to clouds and water vapour. We invite contributions from dedicated field campaigns, from ground-based and satellite remote sensing or in situ measurements, as well as modelling and theoretical studies. This year we particularly welcome early results from the various ongoing model intercomparisons, like EUREC4A-MIP, CP-MIP and Lagrangian LES MIP, but also from the NextGEMS project. We also invite abstracts focusing on the role of mesoscale convective organization, aerosol-cloud interactions, feature tracking and Langrangian cloud modelling.

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.

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).

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, a consequence of intricate ice particle nucleation, secondary ice production 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).

This session aims to advance our comprehension of cold clouds by bringing observation- and modelling-based research together. A diversity of research topics shall be covered, highlighting recent advances in cloud observation techniques, modelling and subsequent process studies:

(1) Airborne, space borne, ground- or laboratory-based measurements and their derived products (e.g. retrievals), which are useful to characterise cloud properties like extent, emissivity, or crystal size distributions, to clarify formation mechanisms, and to provide climatologies.

(2) Process-based, regional and global model simulations that employ observations for better representation of cold cloud microphysical properties and radiative forcing under both current and future climate.

The synthesis of these approaches can uniquely answer questions regarding dynamical influence on cloud formation, life cycle, coverage, microphysical and radiative properties, crystal shapes, sizes and variability of ice particles in mixed-phase as well as ice clouds. Joint observation-modelling contributions are therefore particularly encouraged.

Please also note the session "Atmospheric surface-science and ice nucleating particles" for more experimental studies related to Ice Nucleating Particles (INPs). Abstracts related to ice formation on this more microphysical scale would better fit into this session.

Snow cover characteristics (e.g., spatial distribution, surface and internal physical properties) are continuously evolving over a wide range of scales due to meteorological conditions, such as precipitation, wind, and radiation.
Most processes occurring in the snow cover depend on the vertical and horizontal distribution of its physical properties, which are primarily controlled by the microstructure of snow (e.g., density and specific surface area). In turn, snow metamorphism changes the microstructure, leading to feedback loops that affect the snow cover on coarser scales. This can have far-reaching implications for a wide range of applications, including snow hydrology, weather forecasting, climate modelling, avalanche hazard forecasting, and the remote sensing of snow. The characterization of snow thus demands synergetic investigations of the hierarchy of processes across the scales, ranging from explicit microstructure-based studies to sub-grid parameterizations for unresolved processes in large-scale phenomena (e.g., albedo and drifting snow).

This session is therefore devoted to modelling and measuring snow processes across scales. The aim is to gather researchers from various disciplines to share their expertise on snow processes in seasonal and perennial snowpacks. We invite contributions ranging from “small” scales, as encountered in microstructure studies, over “intermediate” scales typically relevant for 1D snowpack models, up to “coarse” scales, that typically emerge for spatially distributed modelling over mountainous or polar snow- and ice-covered regions. Specifically, we welcome contributions reporting results from field, laboratory, and numerical studies of the physical and chemical evolution of snowpacks. We also welcome contributions reporting statistical or dynamic downscaling methods of atmospheric driving data, representation of sub-grid processes in coarse-scale models, and evaluation of model performance and associated uncertainties.

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.

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. Lightning produces nitrogen oxides, which are a precursor to ozone production. Thunderstorms and lightning are essential parts of the Global Electrical Circuit (GEC) and control the fair weather electric field. They 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
Connections between lightning, climate and atmospheric chemistry
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

The Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) satellite mission aims to improve our understanding of cloud-aerosol-radiation interactions and Earth radiation budget, such they can be modelled with better reliability in climate and numerical weather prediction models. To achieve this objective, EarthCARE will measure the three-dimensional structure of clouds, precipitation and aerosols, together with collocated observations of solar and terrestrial radiation. EarthCARE will provide unique co-registered observations from a suite of four instruments located on a common platform: (1) ATmospheric LIDar (ATLID), Cloud Profiling Radar (CPR), Multi- Spectral Imager (MSI) and BroadBand Radiometer (BBR). EarthCARE global observations include vertical profiles of natural and anthropogenic aerosols, the vertical contribution of ice and liquid water content, the cloud mesoscale distribution, precipitation microphysics, estimates of particle size, convective vertical air motions, as well as of atmospheric radiative heating and cooling profiles.The launch of this joint European-Japanese mission is planned by mid-2024, providing unique data continuing the heritage measurements by CloudSat, CALIPSO and Aeolus, and bridging towards future missions such as NASA's Atmosphere Observing System mission (AOS) or Aeolus-2.

Cloud feedbacks are the dominant uncertainty in assessing global and regional climate sensitivity. As such, improved understanding of the key processes involved in cloud formation, development and radiative effects will support better representations of these processes in climate models and a reduction in the uncertainty in future climate predictions.

Just as cloud formation could be said to begin at the on the surface of aerosol particles, we will begin this session exploring aerosol physics, aerosol generation, emission and properties, and the associated heterogeneous ice nucleation. There will be a particular focus on ice-nucleating particles, which play a fundamental role in clouds with high feedback uncertainty. Atmospheric aerosol-cloud-climate interactions (e.g. heterogeneous nucleation, particle oxidation, photosensitization and the consequent emission of volatile organic compounds (VOCs),...) are also fundamental processes in the atmosphere that regulate energy transfer, cloud dynamics and precipitation formation.

From this aerosol perspective of cloud formation and development, we then look to explore the atmospheric and cloud processes that can influence cloud radiative effect, such as secondary ice production, ocean or land surface variability, meteorology or large-scale atmospheric circulation. Finally, we welcome studies providing theory and quantification of cloud radiative effect and cloud feedback.

This session invites contributions towards reducing the uncertainty in climate sensitivity due to clouds and aerosol-cloud interactions using both observational (in-situ, remote sensing, laboratory) and modelling approaches (process-based or statistical and across the full range of spatial and temporal scales), as well as work leading to a better fundamental understanding of cloud processes, aerosol emissions and ice nucleation processes.

Topics covered in this session are:

- Atmospheric surface-science and the experimental and theoretical approaches investigating the emission and uptake of aerosols in the atmosphere and the relevant atmospheric interactions (e.g. ice nucleation processes and photochemistry at water/air interface) to fill the gap between the large-scale atmospheric processes and gas-, water-, and ice-aerosol interactions.
- Laboratory studies related to aerosol, cloud condensation nuclei, ice nucleating particles or secondary ice processes
- Ice nucleation processes and characterizing INP in the atmosphere
- Modelling and observations of Aerosol-cloud interactions
- Cloud processes and microphysics
- Improving parameterisations associated with cloud formation in models – deep convective clouds, mixed phase clouds, meso-scale convective systems
- Regional cloud drivers, including high latitudes and tropics
- Arctic Amplification and the effect of polar clouds on global climate system
- Cloud feedback and controlling factor analyses
- Effects of circulation on cloud radiative effects and feedbacks


Solicited Speaker: Ottmar Möhler, Institute of Meteorology and Climate Research, Atmospheric Aerosol Research Division (IMK-AAF), Karlsruhe Institute of Technology (KIT), Germany.
Solicited Presentation: "Sources and abundance of ice nucleating particles derived from long-term measurements at high time resolution".

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.

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 their profound local effects, monsoon variability also causes global-scale impacts via teleconnections.

Monsoons are 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 equally welcomed, as is work on impacts, extremes, NWP modelling, S2S and decadal forecasting, and the latest CMIP6 findings. Applications of AI/ML to monsoon studies are also encouraged.

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, with a special focus on the role of Atmospheric Rivers;

* investigating the large-scale drivers behind the past, ongoing and future variability and trends within the atmospheric water cycle, from field campaigns (YOPP, MOSAiC, (AC)3, ISLAS, EUREC4A etc.), long-term observations, reanalysis data, regional to global model simulations, or (isotopic) data assimilation;

* reconstructing past hydroclimates based on paleo-proxy records from archives such as ice cores, lake sediments, tree-rings or speleothems;

* 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;

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

We particularly encourage contributions linking 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 hydrological 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 hydrological cycle for land and water management.

Typically, studies in this session are applied studies using fundamental characteristics of the atmospheric branch of the hydrological 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 investigates mid-latitude cyclones and storms on both hemispheres. We invite studies considering cyclones in all different stages of their life cycles, from initial generation to the final development, including studies to large- and synoptic-scale conditions influencing cyclones’ growth to a severe storm, their dissipation, and related socioeconomic impacts.
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?

Water is a strategic issue in drylands, where ecosystems and their inhabitants strongly rely on the scarce and often intermittent water availability or its low quality. The characteristics of drylands increase their vulnerability to climate change and susceptibility to the impact of short- to long-term extreme events and processes, such as floods, droughts, and desertification. These events can reshape the landscape through the mobilisation of surface sediments, deposits of which preserve archives of past Earth system states, including changes in the extent of deserts. Over the last century, anthropogenic modifications of all kinds and intensities have affected surface conditions. In drylands and Mediterranean hydrosystems, agricultural water use is constantly increasing threatening the sustainability of the surface and groundwater reservoirs, and their hydrology is then continuously evolving. Nevertheless, the study of hydroclimatic processes in drylands remains at the periphery of many geoscientific fields. A proper understanding of the hydrological, hydrometeorological and (paleo)climatic processes in these regions is a cornerstone to achieving the proposed sustainable development goals we set for the end of this century.

This session welcomes contributions from scientific disciplines addressing any of the drylands' full range of environmental and water-related processes. The purpose is to foster interdisciplinary research and expand knowledge and methods established in individual subdisciplines. We will address hydrological issues across global drylands, and devote a section of our session to a geographical focus on the Mediterranean region to analyse the changes in hydrologic processes and fluxes unique to that region.

Extreme hydro-meteorological events drive many hydrologic and geomorphic hazards, such as floods, landslides and debris flows, which pose a significant threat to modern societies on a global scale. The continuous increase of population and urban settlements in hazard-prone areas in combination with evidence of changes in extreme weather events lead to a continuous increase in the risk associated with weather-induced hazards. To improve resilience and to design more effective mitigation strategies, we need to better understand the triggers of these hazards and the related aspects of vulnerability, risk, mitigation and societal response.
This session aims at gathering contributions dealing with various hydro-meteorological hazards that address the aspects of vulnerability analysis, risk estimation, impact assessment, mitigation policies and communication strategies. Specifically, we aim to collect contributions from academia, industry (e.g. insurance) and government agencies (e.g. civil protection) that will help identify the latest developments and ways forward for increasing the resilience of communities at local, regional and national scales, and proposals for improving the interaction between different entities and sciences.
Contributions focusing on, but not limited to, novel developments and findings on the following topics are particularly encouraged:
- Physical and social vulnerability analysis and impact assessment of hydro-meteorological hazards
- Advances in the estimation of socioeconomic risk from hydro-meteorological hazards
- Characteristics of weather and precipitation patterns leading to high-impact events
- Relationship between weather and precipitation patterns and socio-economic impacts
- Socio-hydrological studies of the interplay between hydro-meteorological hazards and societies
- Hazard mitigation procedures
- Strategies for increasing public awareness, preparedness, and self-protective response
- Impact-based forecast, warning systems, and rapid damage assessment.
- Insurance and reinsurance applications

With global climate change affecting the frequency and severity of extreme meteorological and hydrological events, it is particularly necessary to develop models and methodologies for a better understanding and forecasting of present-day weather induced hazards. Future changes in the event characteristics as well as changes in vulnerability and exposure are among the further factors for determining risks for infrastructure and society, and for the development of suitable adaptation measures. This session considers extreme events that lead to disastrous hazards induced by severe weather and climate change. These can, e.g., be tropical or extratropical rain- and wind-storms, hail, tornadoes or lightning events, but also (toxic) floods, long-lasting periods of drought, periods of extremely high or of extremely low temperatures, etc. Papers are sought which contribute to the understanding of their occurrence (conditions and meteorological development), to the augmentation of risks and impacts due to specific sequences of extremes, for example droughts, heavy rainfall and floods, to assessment of their risk (economic losses, infrastructural damages, human fatalities, pollution), and their future changes, to studies of recent extreme events occurring in 2023, to the ability of models to reproduce them and methods to forecast them or produce early warnings, to proactive planning focusing on damage prevention and damage reduction. In order to understand fundamental processes, papers are also encouraged that look at complex extreme events produced by combinations or sequences of factors that are not extreme by themselves. The session serves as a forum for the interdisciplinary exchange of research approaches and results, involving meteorology, hydrology, environmental effects, hazard management and applications like insurance issues.

The frequencies and intensities of extreme events such as floods, tropical cyclones, heat waves, droughts etc. are increased in many regions across the globe and now of serious concern due to their socio-economic Impact. Hence understanding of the mechanism, pattern and characteristics of such events have been the focus of many recent studies. This session invites abstracts on observational and numerical modeling studies aimed to enhance the understanding of the spatial and temporal characteristics and predictability of the extreme events. This session also welcomes the submissions on model simulations and evaluations aimed to advance the understanding of the physics and dynamics associated with the extreme events. In particular, abstracts are encouraged on regional-scale analysis of the historical extreme events and their projections which would assist the policy makers to build more resilient societies to face the extreme event related disasters.

Recent extreme events and climate conditions unprecedented in the observational record have had high-impact consequences globally. Some of these events would have arguably been nearly impossible without human-made climate change and broke records by large margins. Furthermore, compound behaviour and cascading effects and risks are becoming evident. Finally, continuing warming does not only increase the frequency and intensity of events like these, or other until yet unprecedented extremes, it also 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 their impacts, and to better understand how to reduce the risks.

To provide more actionable information for risk assessments, climate storylines have become a popular approach to complement probabilistic event attribution and climate projection. According to the latest IPCC-WG1 report, “the term storyline is used both in connection to scenarios or to describe plausible trajectories of weather and climate conditions or events”. Various types of storylines exist, such as event-based storylines, dynamical storylines of physically plausible climate change, or pseudo-global-warming experiments. This session aims to bring together the latest research on modelling, understanding, development of storylines and managing plausible past and future climate outcomes, extreme and low-probability events, and their impacts. Studies can range across spatial and temporal scales, and can cover compound, cascading, and connected extremes, worst-case scenarios, event-based and dynamical storylines, as well as the effect of tipping points and abrupt changes driven by climate change, societal response, adaptation limits, or other mechanisms (e.g., volcanic eruption).

We welcome a variety of methods aiming to quantify and understand high-impact climate events in present and future climates and, ultimately, provide actionable climate information. We invite work including but not limited to the variety of storyline approaches, model experiments and intercomparisons, insights from paleo archives, climate projections (including large ensembles, and unseen events), and attribution studies.

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

Dynamics, transport processes and chemical composition in the stratosphere and and the related feedbacks are inextricably linked. Changes in any of these aspects are in turn linked to changes in tropospheric circulation, climate, and weather events via two-way coupling. Such changes can be driven or triggered by a variety of natural (e.g., ENSO, QBO, SSWs, solar and volcanic activity, wildfires) and anthropogenic (emissions of radiatively or chemically active gases) processes. Better understanding of these processes and their consequences is important to improving understanding and prediction of changes in weather, climate, and air quality, including those related to extreme weather events. We welcome abstracts based on observational and modelling studies that explore dynamical, chemical, and transport processes in the stratosphere and their links to surface conditions on all time scales. Combined use of modelling and data analysis is particularly encouraged, including climate model and reanalysis comparisons with existing satellite and ground-based datasets, plans for new missions or model / data assimilation development, and studies highlighting new analytical approaches, e.g., based on machine learning, for evaluating and linking stratospheric processes with surface weather and climate.

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 (and around) 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-based) 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 recent field and modelling experiments investigating the impact of extreme events, summer monsoons and convective transport on the UTLS (e.g., volcanic eruptions, wildfires, and the ACCLIP, DCOTTS, and PHILEAS projects).

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, which seek to accurately parameterize the role of IGWs in numerical models.

Recent extreme weather and climate episodes, like the recurrent and concurrent summer heatwaves, summer flooding (e.g. in Germany in 2021 or in Spain in September 2023), or winter cold waves (e.g. in the US in February 2021), highlight the need to further our understanding of the jets and the associated 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 the jets and associated 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.

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 several academic disciplines of geophysics as well as 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. 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, opening 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 and the influence of atmospheric waves on the mean flow. It is expected that further developing multi-instrument platforms will 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 unique opportunities to provide, in near-real time, continuous relevant information about natural hazards with high societal impact, such as volcanic eruptions, surface earthquakes, meteoroids, and bright fireballs.

We invite contributions on recent studies characterizing infrasound sources or atmospheric phenomena using complementary technologies. We particularly encourage presentations utilizing acoustic waves to probe the atmosphere at both small and large scales. Results and advances in acoustic propagation modeling, signal processing and machine learning applications are also welcome. Another focus is on derived data products and services for civilian and scientific applications as well as on innovative instrumentation, which also encompasses sensors attached to moving or elevated platforms such as balloons. We also invite seismo-acoustic studies on the coupled Earth’s crust – ocean – atmosphere system and, in particular, on the ionospheric manifestations of physical processes in the ocean and in the solid Earth.

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.

Mountains cover approximately one-quarter of the total land surface on the planet, and a significant fraction of the world’s population lives in their vicinity. Orography critically affects weather and climate processes at all scales and, in connection with factors such as land-cover heterogeneity, is responsible for high spatial variability in mountain weather and climate. Due to this high complexity, monitoring and modeling the atmosphere and the other components of the climate system in mountain regions is challenging both at short (meteorological) and long (climatological) time scales. This session is devoted to a better understanding of weather and climate processes in mountain and high-elevation areas around the globe, as well as their modification induced by global environmental change.

We welcome contributions describing the influence of mountains on the atmosphere on meteorological time scales, including terrain-induced airflow, orographic precipitation, land-atmosphere exchange over mountains, forecasting, and predictability of mountain weather. Contributions connected with the TEAMx research programme (http://www.teamx-programme.org/) are encouraged.

Furthermore, we invite studies that investigate climate processes and climate change in mountain areas and its impacts on dependent systems, based on monitoring and modeling activities. Particularly welcome are contributions that merge various sources of information and reach across disciplinary borders (atmospheric, hydrological, cryospheric, ecological, and social sciences) and that connect to the Elevation-Dependent Climate Change (EDCC) working group of the Mountain Research Initiative (see https://www.mountainresearchinitiative.org/activities/community-led-activities/working-groups).

The aviation meteorology session will focus on 1) general issues of atmospheric sciences and 2) specifically the use of Uncrewed Aircraft Systems (UAS).
The aviation meteorology session will focus on observations and NWP model applications related to fog, clouds, contrails, ground-based 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, UAS, balloons, 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.
Uncrewed Aircraft Systems (UAS) are an emerging technology, significantly expanding observational capabilities in atmospheric and related sciences. This expansion is enabled by the increased availability and deployment of UAS. This session invites abstracts discussing scientific contributions in atmospheric sciences using various UAS platforms, including fixed-wing UAS, multicopters, and tethered balloon/kite systems (TBS) etc. The topics can include presentations on the development of novel UAS platforms and instrumentation, recent measurement efforts leveraging UAS systems, deployment of UAS to enhance the weather and climate prediction networks, data analysis and synthesis from past UAS field campaigns, and other scientific interpretations of UAS-based datasets to improve process understanding, numerical model prediction, data assimilation and parameterization development.

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.
For both solar and wind power, 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.
• 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.

This session explores climate change, extremes, processes and their impacts at regional to local 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. This also includes high-resolution data sets for the land-surface including urban areas, hydrology, vegetation or similar, and their impacts on local-scale climate change and extremes.

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 and cities
-- 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

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

Urban Boundary Layer (UBL) Dynamics is determined by city morphology, latent and sensible heat fluxes (including anthropogenic heat), and interactions with rural surroundings. The physical processes in such UBLs are characterized by great strong spatial and temporal heterogeneity, and have the potential to affect societally relevant issues like human thermal comfort, air quality, aviation operations and energy supply.
The goal of this session is to highlight research work and promote discussions on this often underrepresented aspect of urban meteorology and climatology. Hence, we invite and encourage contributions on the following topics:

- Numerical modeling of urban boundary layer dynamics at all scales (from regional to street level)
- Observational methods in the UBL: field campaigns and remote sensing (e.g., flux towers, LIDAR, drones)
- Wind tunnel experiments
- Interaction between local circulations (e.g., UHIC, thermal circulation in complex terrain, sea/lake breeze) and the built environment
- Role of turbulent fluxes and impact of turbulence on wind flow
- Intra-canopy and canyon ventilation
- Impact of urban vegetation (e.g., street trees) on wind flow
- Urban air quality (e.g., pollutant transport and dispersion)
- Urban wind energy potential

The session is addressed to experimentalists and modelers working on air-land interactions from local to regional scales including urban and natural terrestrial ecosystems. 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, and processes related to fog, dew, and water vapour adsorption. 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, and biophysical effects.

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 recent field campaigns (e.g. MOSAiC, ALPACA, ARTofMELT, POLAR CHANGE), 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 MOSAiC, ALPACA, ARTofMELT and POLAR CHANGE, 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 during 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.

The ocean surface layer mediates the transfer of matter, energy, momentum and trace gases between the atmosphere, ocean and sea ice, and thus plays a central role in the dynamics of the climate system. This session will focus on the ocean surface layer globally, from the coasts to the pelagic ocean and its interactions with the overlaying low atmosphere. The session covers recent progress in understanding key processes in the ocean surface layer, including wind-driven turbulence, surface-wave effects, convection, surface-layer fronts, surface-layer instabilities, submesoscale dynamics, diurnal warm and rain layers, and surface layer communication with the ocean’s interior. Particular emphasis is placed on the impact of ocean surface-layer processes on air-sea fluxes and feedbacks in field experiments and coupled atmosphere-ocean models. This includes SST coupling with the atmospheric boundary layer, tropical cyclones, extreme events, and parameterizations of air-sea interactions. The interaction of the ocean surface layer with sea ice is also of particular interest. We welcome interdisciplinary studies including atmospheric deposition of nutrients and pollutants to the ocean and impacts on ocean biogeochemistry, ocean-atmosphere fluxes of climate-active species and potential feedbacks to climate. We encourage a diversity of approaches: observational (laboratory, in-situ and remote sensing), theoretical, and numerical modeling studies focusing on the ocean surface layer and its interactions with the atmosphere and sea ice, regardless of the temporal and spatial scales considered. This session also includes a focus on the legacy and activities of the 20-year Surface Ocean - Lower Atmosphere Study (SOLAS) and is jointly sponsored by SOLAS and GESAMP Working Group 38 on ‘The Atmospheric Input of Chemicals to the Ocean’.

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 modelling. 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 interactions between biogenic and anthropogenic emissions. Such interactions may enhance or diminish aerosol formation, growth or lifetime, and they may alter aerosol properties. In general, the effects are non-linear, and key processes may occur in the gas phase, particle phase, or heterogeneously, while involving a wide range of compounds, making for a deep and complex topic. Yet, a major fraction of secondary aerosol globally forms in the confluence of both biogenic and anthropogenic emissions, in particular in and near population centers. We thus invite submissions that fall within this broad topic. This could include work on the role and impact of:
• multi-precursor systems, in particular mixtures of organic aerosol precursors
• volatile chemical products (VCPs)
• oxidized nitrogen species (NOx, NOz)
• reduced nitrogen (for example, emissions of ammonia and amines)
• sulfur-containing species
• heterogeneous and condensed-phase reactions
• altered aerosol particle properties

Organic compounds play a key role in biosphere-atmosphere exchange, anthropogenic emissions, and the reactive chemistry responsible for ozone and particulate matter production. Coming from diverse sources and constituting thousands of individual compounds, with varying oxidation mechanisms, the organic composition of the troposphere is complex. With their wide range of lifetimes and volatilities, these species partition between gas and particle phases and make up a substantial fraction of fine particulate matter. Organics are also a major source of atmospheric reactivity, with implications for the oxidative capacity of the atmosphere. Some individual organic compounds are of interest due to their toxicity or use as specific source tracers. Because of organics’ role in secondary pollutant formation and reactivity, this chemistry is highly relevant to air quality from urban to remote regions. Finally, while global budgets of organic species are central to understanding tropospheric oxidative chemistry and aerosol budgets, they remain poorly constrained.

This session invites contributions about tropospheric organics on local, regional and global scales, from theoretical studies, laboratory experiments, field measurements, modeling studies, satellite studies, and including measurement technique development. The emphasis of this session is on gas-phase organics, including aerosol precursors and semi-volatile species.

Organic aerosols (OA) are a significant fraction of atmospheric particulate matter (PM) in different environments from urban landscapes to pristine regions, and from the boundary layer to the upper troposphere. Due to their complex chemical composition, OA remains one of the least understood parts of PM, with effects on Earth's climate and human health that are still inadequately characterized. Ongoing research efforts enhance our understanding of the origin and (trans)formation processes of (secondary) OA. This encompasses studying natural sources and assessing how anthropogenic emissions change the chemical composition and physical properties of organic aerosols.
This session welcomes submissions on ambient and chamber studies of OA, which contribute to a deeper understanding of their origins (such as secondary OA formation or biomass burning), analysis of the molecular composition (e.g. targeted analysis of organic pollutants), investigation of physico-chemical properties, exploration of atmospheric transformation reactions (for example aging or brown carbon formation), and examination of gas-to-particle partitioning of organic molecules.

Deserts and oceans represent the two most abundant sources of natural aerosols. Dust particles impact the Earth’s energy budget through interactions with radiation and clouds, and affect the marine biogeochemical cycle. Marine aerosols, including primary sea spray aerosols and secondary aerosols, play a critical role in the interconnections between the ocean and the atmosphere. Consequently, they play significant roles in shaping the climate. Comprehending the physicochemical properties, formation mechanisms, and effects of these two distinct types of natural aerosols is of utmost significance. Recent topics of interest include organic aerosols, halogen, and alkali elements for marine aerosols. Additionally, there is active research into the transformation, impacts on marine ecosystems, and radiative effects of dust. In this session, we welcome new understandings and findings on the formation, transformation, and deposition processes, as well as the environmental and climatic effects of aerosols from desert to marine environments based on field observations, lab, and modeling studies.
Topics include, but are not limited to:
Chemical compositions, morphology, and physicochemical properties of marine and dust aerosols,
Formation and transformation of marine organic aerosols and dust aerosols,
Heterogeneous chemistry on marine and dust aerosols and their aging processes,
Effects of marine biogeochemistry on marine organic aerosols,
Impacts of anthropogenic pollutants on marine and dust aerosols,
Environmental and climatic impacts of marine and dust aerosols.

Dust aerosols are one of the most important components in the atmosphere, which are mainly originated from the dust aerosol belt along the African and Asian Continents (DAAC). Dust events cannot carry only mineral particles but also bioaerosols such as bacteria and fungi, and allow them travel for long distance from their origin. The effects of dust aerosols and bioaerosols on ecosystems and climate changes are complicated as the effects of dust and bioaerosols on clouds and precipitation are not yet clear, and the simulation of dust aerosols and the detection and classification of bioaerosols remain a major technical challenge. As such, accurately quantifying dust aerosols and bioaerosols, understanding their impacts is of importance to an increasingly diverse range of research communities. The further researches remarkably needed to investigate the emission sources, transport mechanisms, and climate impacts of dust and bioaerosols along the DAAC, the impact of allergenic species on public health and air quality, and how changes introduced by net zero policies affect this. Therefore, observations along with regional and global modelling are required to gain a comprehensive understanding of the roles of dust aerosols and bioaerosols in climate system.
The goal of the proposed session is to discuss with worldwide scientists together and to gain more insight into the different aspects of the dust aerosols and bioaerosols including but not limited to topics: (1) dust source contribution, transport mechanisms and processes using observations and modelling; (2) bioaerosols observations based on real-time detection, laboratory studies, machine learning data processing techniques and model simulations; (3) exposure assessment and associated health impacts of bioaerosols; (4) impacts of dust and bioaerosols on climate, environment as well as ecosystem.

The interactions between aerosols, climate, weather, and society are among the large uncertainties of current atmospheric research. Mineral dust is an important natural source of aerosol with significant implications on radiation, cloud microphysics, atmospheric chemistry, and the carbon cycle via the fertilization of marine and terrestrial ecosystems. Together with other light-absorbing particles, dust
impacts snow and ice albedo and can accelerate glacier melt. In addition, properties of dust deposited in sediments and ice cores are important (paleo-)climate indicators.

This interdivisional session -- building bridges between the EGU divisions AS, CL, CR, SSP, BG and GM -- had its first edition in 2004 and it is open to contributions dealing with:

(1) measurements of all aspects of the dust cycle (emission, transport, deposition, size distribution, particle characteristics) with in situ and remote sensing techniques,
(2) numerical simulations of dust on global, regional, and local scales,
(3) meteorological conditions for dust storms, dust transport and deposition,
(4) interactions of dust with clouds and radiation,
(5) influence of dust on atmospheric chemistry,
(6) fertilization of ecosystems through dust deposition,
(7) interactions with the cryosphere, including also aerosols other than dust,
(8) any study using dust as a (paleo-)climate indicator, including sediment archives in loess, ice cores, lake sediments, ocean sediments and dunes,
(9) impacts of dust on climate and climate change, and associated feedbacks and uncertainties,
(10) implications of dust for health, transport, energy systems, agriculture, infrastructure, etc.

We especially encourage the submission of papers that integrate different disciplines and/or address the modelling of past, present, and future climates.

Solicited speaker: Keri Nicoll, University of Reading, "Recent developments in dust electrification research"

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.

There are several other related sessions on aerosols, clouds, radiation and precipitation processes focused on specific themes (see links below)

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

Anthropogenic and natural aerosols play key roles in driving climate change over a range of spatial and temporal scales, both close to emission sources and also remotely through teleconnections. Aerosols can directly interact with radiation by scattering and absorption and indirectly through modulating cloud properties, and thereby modify the surface and atmospheric energy balance, cloud dynamics and precipitation patterns, and the atmospheric and oceanic circulation. Changes in regional aerosol emissions accelerate greenhouse gas-driven climatic changes in some regions, counteract them in others, and may interact with natural variability to further stress human and ecological systems. However, our understanding of these impacts still lags those due to greenhouse gases. The poor aerosol integration in many climate risk and impact studies currently leads to potentially dangerous omissions in projections of near-term climate change impacts.

This session addresses: the strong and spatially complex trends in temperature, hydroclimate, air quality, and extreme events driven by aerosol changes over the historical era, and those expected in the near future; the interplay between aerosol-driven changes and those induced by other forcing factors; and their extensions to climate risk and impact studies. We encourage contributions based on model and observation-based approaches to investigate the effects of aerosols on regional decadal climate variability and extremes, tropical-extratropical interactions and teleconnections, and the interactions with modes of variability such as the NAO, ENSO, AMV, and PDO. We also welcome focused studies on monsoon systems, midlatitude and Arctic responses, extreme temperature and precipitation, atmospheric and oceanic circulation changes, tropical cyclones, and daily variability, using for example CMIP6 projections, large ensemble simulations, or specifically designed experiments. We especially encourage studies focusing on climate risk and concrete regional impacts on nature and society resulting from changes in anthropogenic and natural aerosol emissions.

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 stratosphere and climate impacts from the 2022 eruption of Hunga Tonga are also 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, CMIP7-VolMIP, CMIP7-PMIP, and PAGES-VICS.

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.
- Studies on ozone production and loss processes and how these might change under future emission scenarios.
- Global and regional model studies of past and future ozone changes and their attribution.
- 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 including those from members of the Tropospheric Ozone Assessment Report (TOAR) Phase II working groups.

The Earth's middle atmosphere, mesosphere, and lower thermosphere (MLT) region provide a great platform for studying ionospheric dynamics, disturbances, eddy mixing, atmospheric drag effects, and space debris tracking. The thermal structure of these regions is influenced by numerous energy sources such as solar radiation, chemical, and dynamical processes, as well as forces from both above (e.g. solar and magnetospheric inputs) and below (e.g. gravity waves and atmospheric tides). Solar atmospheric tides, related to global-scale variations of temperature, density, pressure, and wind waves, are responsible for coupling the lower and upper layers of the atmosphere and significantly impact their vertical profiles in the upper atmosphere. With evidence of climate change impacts on the middle and upper atmosphere, monitoring and understanding trends through observational data is critical. There has been a contraction of the stratosphere and a decrease in the density of the upper atmosphere, which could impact the accumulation of space debris. 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 ~ 20 km to 180 km of the middle atmosphere and MLT regions, including long-term climatic changes.

The weather and atmospheric composition (AC) are closely related. Still, Numerical Weather Prediction (NWP) and AC forecasts are often operated independently. However, recognizing the scientific and operational benefits of combining NWP and AC forecasting and data assimilation, integrated AC-NWP systems for global, regional, and local applications have been developed.

We invite contributions on all aspects of forecasting and data assimilation of aerosols, reactive gases, greenhouse gases, and weather or stratospheric dynamics across different time scales. Our focus is on the scientific, computational, and societal advantages of such integrated approaches. Specifically, but not exclusively, we invite papers addressing the following topics:

a) Improved NWP from short timescales to seasonal scales due to feedbacks between aerosols, chemistry and radiation and cloud physics,

b) Parameterization of weather-composition feedbacks in radiation and cloud physics,

c) Impact of the uncertainty of meteorological simulations on AC predictions,

d) Advancements in designing and developing operational coupled NWP-AC prediction systems,

e) Satellite retrievals of meteorological variables in the presence of aerosols,

f) Data assimilation developments for AC and NWP,

g) Forecasting of stratospheric composition and dynamics after large volcanic eruptions such as the Hunga-Tonga,

h) Combined impact of environmental hazards on society, such as air pollution and high-impact weather, wildfires, dust storms and the underlying meteorological factors,

i) Evaluation, validation, and applications of NWP-AC predication systems.

This Session is organized in cooperation with the Copernicus Atmosphere Monitoring Service (CAMS) and the Global Air Quality Forecasting and Information Systems (GAFIS) initiative and the Modeling Applications Science Advisory Group (SAG-APP) of the WMO Global Atmosphere Watch (GAW) Program.

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.

Air pollution remains a pressing global issue, prompting nations worldwide to implement various mitigation strategies, often targeting specific pollutants such as particulate matter. While these strategies are crafted with the best intentions, they sometimes yield unwanted effects, including alterations in atmospheric chemical compositions leading to phenomena like ozone increase or unforeseen climate impacts.

This session aims to shed light on the unintended consequences of air pollution mitigation strategies, focusing on the changes in chemical composition induced by these strategies. We invite contributions that delve into the observational data, modeling approaches, and projections of future changes to better understand the full spectrum of effects stemming from pollution control measures.

By fostering a discussion grounded in rigorous scientific analysis, we hope to pave the way for more holistic and effective strategies in the future, balancing the urgent need for pollution reduction with a deep understanding of potential unwanted effects.

We welcome submissions that employ a range of research methods including, but not limited to, observational studies and modeling to forecast future changes, encouraging a multidisciplinary approach to a complex issue.

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.

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)

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.

The transport sector, which includes road traffic, shipping, and aviation, is a significant contributor to global warming and has a negative effect on air quality. The combustion of fossil fuels results in the emission of gases and particles that alter the chemical composition of the atmosphere. These gases can act as direct greenhouse gases, such as CO2, or undergo complex reactions, forming secondary species. The emitted particles interact with radiation and affect clouds. Emissions from aviation can also lead to the formation of contrails, which affect natural cloud formation processes. While some of these non-CO2 effects contribute to global warming and others to cooling, the overall warming contribution of transport emissions is predominant.

Due to the significant increase in demand, the contribution of aviation to climate change is expected to grow. Additionally, emissions from road traffic and shipping may also increase depending on changes in mobility and technological advancements. Therefore, it is crucial to develop and implement measures and methods to reduce the anthropogenic climate footprint, including the share of different transport modes. Possible methods to reduce the environmental impact of aviation include alternative fuels, such as electricity or hydrogen, and technological advancements, such as after-exhaust treatment systems.

However, the assessment of the effects of such measures and methods with numerical atmospheric models relies heavily on state-of-the-art emission inventories. It is crucial to provide information on the uncertainties in the emission data to ensure a dependable assessment of air quality and climate effects. This information also contributes to the uncertainties in the representation of physical, chemical, and dynamic processes in atmospheric models.

The objective of this session is to bring together the community involved in the development of transport emissions inventories with the community involved in the use of these inventories. On one hand, the aim is to establish a shared understanding of the different requirements and uncertainties related to emission inventories. On the other hand, particular attention will be given to the latest research on the non-CO2 effects of aviation. Contributions can range from measurement campaigns to modelling results and implementing strategies for integrating climate effect reduction in flight planning.

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 these interactions with a particular emphasis on the impacts of a move to a hydrogen economy.

Hydrogen has been suggested as a promising candidate for decarbonizing various sectors, such as transportation, industry and energy production in a transition to a low-carbon society. A hydrogen economy presents opportunities for reducing greenhouse gas emissions and mitigating climate change, but it also poses significant challenges and has many associated uncertainties. Although hydrogen is not a greenhouse gas itself, leakages to the atmosphere lead to impacts on other greenhouse gases and aerosols. The atmospheric hydrogen budget is uncertain. This is mainly because of uncertainties in its largest sink, uptake by microbes in soils, but many other source and sink terms are also not well known. This session welcomes contributions to better understand the hydrogen budget and the potential impacts of widening hydrogen use, including through: using observations; quantification of the indirect climate effects from hydrogen emissions on methane, ozone, stratospheric water vapour and aerosols; measurements and quantification of hydrogen leakages; and scenarios of possible future hydrogen economies, including the associated co-benefits of reducing fossil fuel emissions for the climate and environment.

Fire is the primary terrestrial ecosystem disturbance globally and a critical Earth system process. Fire-related research is rapidly expanding across disciplines and sectors, reflecting the pressing need to deepen our understanding of fire phenomena. This need will likely grow as future fire activity increases. This session invites contributions that investigate the role of fire within the Earth system across any temporal and spatial scale, using statistical (including AI) and process-based models, field and laboratory observations, proxy records, remote sensing, and data-model fusion techniques. We strongly encourage abstracts that deepen our comprehension of fire's interactions with: (1) weather, climate, atmospheric chemistry, and circulation, (2) land physical properties, (3) vegetation composition and structure and biogeochemical cycle, (4) cryosphere elements and processes (such as permafrost, sea ice), and (5) human health, land management, conservation, and livelihoods. Moreover, we welcome submissions that address: (6) spatial and temporal changes in fire in the past, present, and future, 7) fire products and models, and their validation, error/bias assessment and correction, as well as (8) analytical tools designed to enhance situational awareness for fire practitioners and to improve fire early warning systems.

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.

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.

A constellation of geostationary satellite ultraviolet-visible (UV-VIS) spectrometers with air quality related trace gas and aerosol observational capabilities will soon be in orbit forming a Geo-Ring. These include Geostationary Monitoring Spectrometer (GEMS) launched in January 2020 by Korean Aerospace Research Institute for National Institute of Environmental Research over Asia, Tropospheric Emissions: Monitoring of Pollution (TEMPO) launched in April 2023 by NASA over North America, and the Copernicus Sentinel-4 ultraviolet visible near infrared (UVN) instrument developed by the European Space Agency and to be launched in 2024/2025 over Europe. Both GEMS and Copernicus Sentinel-4 have operational continuity and for TEMPO, NOAA’s GeoXO atmospheric composition instrument (ACX) will be an operational follow-on. A very successful demonstration of tropospheric air quality observational capability by Ozone Monitoring Instrument (OMI) and Tropospheric Monitoring Instrument (TROPOMI) in Low Earth Orbit laid the foundation for similar instruments in geostationary orbit, expanding the observations from daily to hourly time scales. We are soliciting papers on global hourly observations of different pollutants from Geo-Ring, consistency of products with state of the art calibration and validation including TROPOMI as a transfer standard for Level 1B radiances, usage of trace gas and aerosol data in models, inverse modeling to derive emissions, long-range transport of pollutants, and related topics along with international collaborations.

Significant uncertainties exist in our understanding of Carbon Dioxide (CO2) and Methane (CH4) fluxes between land, ocean, and the terrestrial atmosphere on regional and global scales. Remotely-sensed CO2 and CH4 observations provide a significant potential for improving our understanding of the natural carbon cycle and for monitoring anthropogenic emissions. Over the last few years, remote sensing technologies for measuring CO2 and CH4 from space, aircraft, and from the ground made great advances offering unprecedented accuracy and coverage. Additionally, upcoming and planned next-generation platforms such as CO2M, MicroCarb, GOSAT-GW, and MethaneSAT are set to substantially improve observational capabilities. When integrated with data from ground-based observation networks and modeling tools, these space-based observations have the potential to significantly enhance our understanding of the carbon cycle on both local and global scales.

This session is open to contributions related to all aspects of remote sensing of the greenhouse gases CO2 and CH4 from current missions (e.g. GOSAT/2, OCO-2/3, S5P, GHGSat, etc.), upcoming and planned satellite missions (e.g. CO2M, MicroCarb, Merlin, GOSAT-GW, MethaneSAT, etc.), as well as ground-based (e.g., TCCON, COCCON), aircraft, and other remote sensing instruments. This includes advances in retrieval techniques, instrumental concepts, and validation activities, but we specifically encourage contributions that focus on the interpretation of observations with respect to natural fluxes or anthropogenic emissions.

Atmospheric radicals (OH, HO2, RO2, NO3, and halogen oxides) drive the oxidation of trace gases, promoting secondary pollution formation and influencing the climate. Understanding the sources (reactive species, e.g. HCHO, HONO, ClNO2 etc.) and chemical fate (conversion of primary pollutants and oxidation of CH4) of radicals is fundamental to tackle regional pollution and climate change. Measuring and modelling radicals is important but extremely challenging due to their low concentration, high reactivity and the complexity of reactions that they initiate.

This session invites results relating to radical measurements and modelling including:
1. The development of different techniques for radical detection, their precursors and intermediates species;
2. The adaption of instruments to different platforms (ground, mobile, shipborne, airborne, etc.);
3. Quality assurance (e.g. calibration procedures, inter-comparison of different techniques);
4. Model development (e.g. new chemical reactions/mechanisms, new model configuration, uncertainty analysis);
5. The implementation of radical measurements and modelling in the field and in chamber studies.

We welcome contributions involving the use of stable isotopes of light elements (C, H, O, N, S) or novel tracers (such as COS) in field and laboratory experiments, the latest instrument developments, as well as theoretical and modelling activities, which advance our understanding of biogeochemical and atmospheric processes. We are particularly interested in the latest findings and insights from research involving:

- Isotopologues of carbon dioxide (CO2), water (H2O), methane (CH4), carbon monoxide (CO), oxygen (O2), carbonyl sulfide (COS), and nitrous oxide (N2O)
- Novel tracers and biological analogues
- Polyisotopocules including "clumped isotopes"
- Non-mass-dependent isotopic fractionation and related isotope anomalies
- Intramolecular stable isotope distributions ("isotopomer abundances")
- Quantification of isotope effects
- Analytical, methodological, and modelling developments
- Flux measurements

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.

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.

Atmospheric observations of greenhouse gases, organic and inorganic trace gases, and aerosols serve as the foundation for quantifying radiative forcing within the climate system and for monitoring trends in air quality. To ensure coherent measurements and global data comparability a robust metrological support infrastructure is required. This session invites contributions aimed at addressing the science necessary to underpin long-term ambient monitoring of trace gases and aerosols encompassing innovative measurement methods and instrumentation, rigorous measurement validation, advancements on standards and scales, uncertainty quantification, quality control and assurance protocols, as well as comparisons in round-robins or of standards at the calibration laboratory level. Aligned with the network comparability objectives outlined by the World Meteorological Organization (WMO), this session underscores the routine observation of ambient amount fractions and stable isotope ratios spanning various trace gases, including major greenhouse gases CO2, CH4, and N2O. It also encompasses ambient trace gas amount fractions, particle number concentrations and size distributions, routinely monitored across global networks of observation sites and mobile measurement platforms. Long-term tracking of spatial and temporal variations in ambient gaseous and aerosol concentrations plays a pivotal role in establishing scientific links and feedback mechanisms within Earth's atmosphere, crucial for comprehending the intricate connections between atmospheric composition, air quality, and climate, and ensuring compliance with legislative mandates. Upholding the quality and comparability of these vital measurement datasets is instrumental in advancing reliability and reducing uncertainty in our comprehension of Earth's system, making your active involvement indispensable in shaping the future of trace gas and aerosol monitoring and contributing to reaching the required network comparability goals for all Essential Climate Variables.

Accurate and precise, long-term measurements of greenhouse gas (GHG) concentrations continue to show 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, implementing, 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) and WMO’s newly established Global Greenhouse Gas Watch (GGGW) initiative. These initiatives, together with other national and international, efforts seek 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, GHG fluxes, 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, modeling and analysis methods.

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, together with statistical and novel means of tracking emissions activity data-driven, as well as hybrid combinations of both approaches for GHG monitoring and improved emission inventory estimates that deliver actionable GHG information. Actionable information must have the needed temporal and spatial details to target and track explicit emission activity where climate action is achievable from facilities to cities to nations and ultimately our ability to determine the integrated efficacy of our emission reduction efforts at the global scale in support of Paris agreement stocktake.

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 that seek to quantify global and regional budgets, trends and variability of major GHG (N2O, CH4 and CO2), as well as to understand the key drivers and processes controlling their variations. We welcome contributions using a variety of approaches, such as 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 phase 2 (RECCAP2), as well as studies integrating different datasets and approaches at multiple spatial (regional to global) and temporal scales (from past over the present and to the future) that provide new insights on processes influencing GHG budgets and trends.