The session welcomes papers on:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

We invite studies

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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