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.

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

This session encompasses the development, testing and application of novel numerical techniques for Earth system models, including governing equations, horizontal and vertical discretizations, structure preserving methods, time stepping schemes, advection schemes, adaptive multi-scale models, physics-dynamics coupling, regional and global models, classical and stochastic physical parameterizations (that are not covered in other sessions).

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 presentations on high-resolution simulations of weather and climate. This includes state-of-the-art global storm-resolving simulations for weather and climate prediction but also large-eddy simulations and high-resolution ocean modelling. Presentations can cover developments to improve model fidelity (e.g. via improved parametrisations), detailed studies of modelled phenomena at high-resolution (e.g. tropical cyclones) and the impacts of ocean-atmosphere coupling. However, reflecting the technical challenges of such simulations, we also welcome presentations about computational concerns, such as the effective use of heterogeneous supercomputers (including GPUs), domain-specific languages, and the development of new, efficient dynamical cores. We also welcome presentations from participants of international projects related to high-resolution weather and climate simulation, such as DYAMOND, PRIMAVERA, Destination Earth, NextGEMS and WarmWorld.

The variability in the stratosphere is important for many atmospheric phenomena. Examples include the dynamical two-way coupling between the stratosphere and troposphere, the transport of trace gases through the meridional circulation of the stratosphere, or the connection between the Quasi-Biennial Oscillation of the tropical stratosphere and the Madden-Julian Oscillation. This session is interested in the causes for and consequences of stratospheric circulation variability, including the mechanisms behind the vertical coupling between the stratosphere and troposphere in tropics and extratropics, and the role of stratospheric dynamics for short-term atmospheric weather, sub-seasonal to seasonal predictability, and long-term climate variability. We welcome abstracts that study these problems from observational, modelling, or theoretical viewpoints on all temporal and spatial scales.

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

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

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

Internal gravity waves (IGWs) still pose major questions both to the atmospheric and ocean sciences, and to stellar physics. Important issues are 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 subtropics present unique regional hydroclimates across the globe, with strong influence from both tropical and mid-latitude dynamics and an extensive interplay between atmospheric thermodynamics, dynamics, and coupled ocean processes. With dependence on both tropical and extratropical processes, subtropical regions are emerging as hotspots of contemporary climate change. These hotspots reflect the paleoclimatological records of high climate sensitivity in subtropical climes (e.g. Green Sahara and Arabia, pluvials in the drylands of southern Africa, Australia). The complexity of subtropical climates present fundamental challenges to develop coherent theories of subtropical climate dynamics, resulting in large uncertainties in climate model simulations. To address these gaps in the understanding of the subtropical climate, we invite contributions focused on subtropical processes and their simulation including:
• diagonal convergence zones
• tropical-extratropical interactions
• subtropical jet fluctuations
• interplays between monsoons and mid-latitude transients
• weather and climate extremes in the subtropics
• analyses of climate simulations looking into past, present and future change in the subtropics
• development of bespoke climate services based on advances in subtropical theory and prediction

Storm and convective scale weather data analysis and prediction still present significant challenges for atmospheric sciences. Addressing them requires synergy of advances in observing at these scales and in data assimilation with convective scale models. This session invites contributions from developments in
• Convective scale data assimilation techniques
• Model uncertainty representation in convective scale data assimilation
• Remote sensing observations at convective scales: data products, observing strategy, and technology
• Assessment of the impact of convective scale data assimilation development, and new observations, on prediction

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, modelling studies, and theoretical investigations 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 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.
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?

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 particularly 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.

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 that provides state-of-the-art precipitation estimates (including solid precipitation) from space with unprecedented accuracy, time-space coverage, and improved information for microphysics.

Cloud and precipitation processes are still a main source of uncertainties in numerical weather prediction and climate change projections. During recent years, large progress has been made in implementing those processes in a more realistic way and with a higher level of detail in models. Simultaneously, also our observational capabilities, especially in the field of radar remote sensing, has been substantially improved by the availability of large national networks, improved instrument accuracy, and also new and more affordable technology. Radar polarimetry in particular is known for its high information content of cloud and precipitation processes. Complementary radar observations, such as polarimetric Doppler spectra or multi-frequency cloud radar observations are also increasingly used to further extend our ability to derive characteristic fingerprints of those processes and inform atmospheric models.
This session invites contributions, which combine radar polarimetry or cloud radars with atmospheric models for an improved understanding of moist processes, numerical model evaluation, or parameterization development, as well as studies advancing the direct assimilation of polarimetric measurements or polarimetry-derived information. The combination of radar polarimetry, atmospheric modelling and data assimilation is also the focus of the German research initiative PROM (Polarimetric Radar Observations meet atmospheric Modelling). We invite contributions from all scientists working at the intersection of these fields.

Ice and mixed-phase clouds play an important role in the Earth’s radiation budget because of their high temporal and spatial coverage. 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 ice cloud processes, their radiative effects, and their interaction with their environment (in particular, aerosols).

This session aims to advance our comprehension of ice clouds by bringing observation- and modelling-based research together.

A diversity of research topics shall be covered, highlighting recent advances in ice cloud observation techniques, modelling and subsequent process studies:

(1) Airborne, spaceborne, ground- or laboratory-based measurements and their derived products (retrievals), which are useful to constrain ice cloud properties like extent, emissivity, or crystal size distributions, to clarify formation mechanisms, and to provide climatology.

(2) Process-based, regional and global model simulations that employ observations for better representation of ice-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 ice 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.

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 the 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).

Mesoscale convective systems (MCSs) and meso-scale storms/disturbances are known to be important precipitation producing/triggering systems in high-mountain environments and on high-altitude plateaus. These meso-scale convective systems and disturbances can lead to severe weather locally and affect lower lying downstream regions.

The aim of this session is to gain an improved understanding of meso-scale systems and the associated processes leading to (extreme) precipitation in mountain regions and/or their downstream areas. We invite contributions on the dynamics of meso-scale storms/disturbances and meso-scale convective systems (including their formation and evolution) as well as smaller-scale convection in connection to atmospheric meso-scale features and how these factors explain spatio-temporal patterns of precipitation and precipitation dynamics. Contributions focussing on individual extreme events or giving climatological perspectives are welcome. Due to the nature of high-mountain environments it is difficult to directly observe their meso-scale atmospheric features and link these to the occurrence and spatio-temporal variability of precipitation. Therefore, contributions integrating remote sensing data, in-situ observations, and high-resolution models, especially those that explicitly resolve convections are particularly welcome.

This session is connected to the recently launched WRCP-CORDEX flagship pilot study “High resolution climate modelling with a focus on mesoscale convective systems and associated precipitation over the Third Pole region”.

The 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 all 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.

This joint session invites papers that are related to the mesosphere and lower thermosphere. It addresses the predictability of the solar-terrestrial coupling, focusing on the role of the sun and the middle atmosphere/thermosphere/ionosphere in climate and space weather. Contributions studying radiation, chemistry, energy balance, atmospheric tides, planetary waves, gravity waves, neutral-ion coupling, and the interaction of the various processes involved are welcome. This includes work on model data as well as measurements from satellites and ground based platforms such as ALOMAR.

This session invites contributions that span all aspects of prediction and predictability in the 2 weeks to 2 months lead time range. The session welcomes contributions on physical processes, prediction methods, impacts, and climate services. We encourage studies of phenomena such as the Madden Julian Oscillation (MJO), tropical/extratropical wave dynamics, teleconnections, stratosphere - troposphere coupling, land - atmosphere coupling, ocean - atmosphere coupling, in addition to studies of predictability and skill of atmospheric or surface variables such as sea ice, snow cover, and land surface, and case studies of extreme or high impact weather events. Contributions regarding impact studies, applications, and climate services at the S2S time-scale are also highly welcome, including, but not limited to, the areas of hydrology, health, fire, agriculture, and energy. These can include modeling studies of the impacts and presentations of how S2S-derived information can be integrated into decision support systems at the local, regional and country level.

The polar climate system is strongly affected by interactions between the atmosphere and the cryosphere. Processes that exchange heat, moisture and momentum between land ice, sea ice and the atmosphere play an important role in local-to-global processes. Atmosphere-ice interactions are also triggered by synoptic weather phenomena such as cold air outbreaks, polar lows, atmospheric rivers and Foehn winds. However, our understanding of these processes is still incomplete. Despite being a crucial milestone for reaching accurate projections of future climate change in Polar Regions, deciphering the interplay between the atmosphere, land ice and sea ice on different spatial and temporal scales, remains a major challenge.
This session aims at showcasing recent research progress and augmenting existing knowledge in polar meteorology and climate and the atmosphere-land ice-sea ice coupling in both the Northern and Southern Hemispheres. It will provide a setting to foster discussion and help identify gaps, tools, and studies that can be designed to address these open questions. It is also the opportunity to convey newly acquired knowledge to the community.
We invite contributions on all observational and numerical modelling aspects of Arctic and Antarctic meteorology and climatology, that address atmospheric interactions with the cryosphere. This may include but is not limited to studies on past, present and future of:
- Atmospheric processes that influence sea-ice (snow on sea ice, sea ice melt, polynya formation and sea ice production) and associated feedbacks,
- The variability of the polar large-scale atmospheric circulation (such as polar jets, the circumpolar trough and storm tracks) and impact on the cryosphere (sea ice and land ice),
- Atmosphere-ice interactions triggered by synoptic and meso-scale weather phenomena such as cold air outbreaks, katabatic winds, extratropical cyclones, polar cyclones, atmospheric rivers, Foehn winds,
- Role of clouds in polar climate and impact on the land ice and sea ice through interactions with radiation,
- Teleconnections and climate indices and their role in land ice/sea ice variability.
Presentations including new observational (ground and satellite-based) and modelling methodologies specific to polar regions are encouraged. Contributions related to results from recent field campaigns in the Arctic and in the Southern Ocean/Antarctica are also welcomed.

The North Atlantic exhibits a high level of natural variability from interannual to centennial time scales, making it difficult to extract trends from observational time series. Climate models, however, predict major changes in this region, which in turn will influence sea level and climate, especially in western Europe and North America. In the last years, several observational projects have been focused on the Atlantic circulation changes, for instance ACSIS, RACE, RAPID, OSNAP, and OVIDE. Another important issue is the interaction between the atmosphere and the ocean as well as the cryosphere with the ocean, and how this affects the climate.

We welcome contributions from observers and modelers on the following topics:

-- climate relevant processes in the North Atlantic region in the atmosphere, ocean, and cryosphere
-- response of the atmosphere to changes in the North Atlantic
-- atmosphere - ocean coupling in the North Atlantic realm on time scales from years to centuries (observations, theory and coupled GCMs)
-- interpretation of observed variability in the atmosphere and the ocean in the North Atlantic sector
-- comparison of observed and simulated climate variability in the North Atlantic sector and Europe
-- dynamics of the Atlantic meridional overturning circulation
-- variability in the ocean and the atmosphere in the North Atlantic sector on a broad range of time scales
-- changes in adjacent seas related to changes in the North Atlantic
-- role of water mass transformation and circulation changes on anthropogenic carbon and other parameters
-- linkage between the observational records and proxies from the recent past

This session merges CL3.1.3 “Climate change and other drivers of environmental change: Developments, interlinkages and impacts in regional seas and coastal regions” focused on regional seas and coastal regions worldwide, and CL3.1.4 “Climate change in Mediterranean-type climate regions” focused on the Mediterranean-type climates, with a very similar scope: how climate change and other drivers affect these regions now and in the future.
Regional climate change interacts with many other man-made perturbations in both natural and anthropogenic coastal environments. Regional climate change is one of multiple drivers, which have a continuing impact on terrestrial, aquatic and socio-economic (resp. human) environments. These drivers interact with regional climate change in ways, which are not completely understood.
A Mediterranean-type climate is characterized by mild, wet winters and hot, dry summers as classified with the Koppen-Geiger approach that is well suited for identifying and analyzing the impacts of climate change on natural and anthropic ecosystems. Mediterranean climate regions (MCRs) are located in transitional midlatitude regions like the Mediterranean basin area, western coastal North America and small coastal areas of western South America, southern Africa and southern Australia. The transitional character with sharp spatial gradients makes them highly vulnerable to climate change. For all MCRs, the future holds high risks and uncertainty on issues like loss in biodiversity, increase in aridity, ecological change, requiring innovative approaches to climate adaptation and mitigation.
This session focuses on the connections and interrelations between climate change and other drivers of environmental change in MCRs, regional seas and coastal regions. It intends to strengthen the exchanges among the communities involved to better understand and share commonalities and differences and to provide an overview of the current state of knowledge of the complicated interplay of different factors affecting climate change. This exchange may help identify and prepare shared solutions and practices. Studies focused on physical (including extremes, teleconnections, hydrological cycle) and biogeochemical (including biodiversity) aspects of Mediterranean and other coastal climate regions, focusing on observed past changes, future climate projections, as well as related social aspects including indigenous knowledge in mitigating climate risks will be treated.

In his seminal work "Weather Prediction by Numerical Process" in 1922, Lewis Fry Richardson proposed his famous cascade picture qualitatively, for a turbulent flow where the energy is transferred from large scale structures to small scale ones, until reaching viscosity scales where it is converted to heat. This picture now has been widely adopted to describe different type of turbulent phenomena, for not only the classical hydrodynamic turbulence, but also, not limited to, the movement of atmosphere and oceans.

After 100 years of developments, the concept of cascades has been extended significantly. Now, it describes mainly the nonlinear interactions crossing a large range of scales where scale invariants might emerge spontaneously. More precisely, balances between the external forcing and the dissipation are expected for a turbulent system. However, due to the complexity of atmospheric or oceanic systems, such as earth rotation, stratification, large aspect ratio, mesoscale eddies, ocean current, tidal, waves, etc., the exact balance is still unknown. We still lack an efficient methodology to diagnose the scale-to-scale energy or other physical quantities fluxes to characterize the cascade quantitatively, e.g., strength, direction, etc.

With the increasing capability of remote sensing, computational fluid dynamics, field observation, etc., we have accumulated a large amount of field data. It is now a suitable time to celebrate the 100th Anniversary of Richardson's idea of cascades in the geosciences, and to understand it quantitatively.
This interdisciplinary session welcomes theoretical, methodological, laboratory, data analysis works that aim to characterize the cascade in atmosphere and oceans and other fields.

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 and loads) on short and long time scales for wind power development, especially in complex environments (e.g. mountains, forests, coastal or urban).
• 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 to 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.

Heat extremes are already one of the deadliest meteorological events and they are projected to increase in intensity and frequency due to rising CO2 emissions. The hazard these events pose to society may therefore increase dramatically, and society will need to adapt if the worst impacts are to be avoided. This session therefore welcomes a broad range of new research addressing the challenge of extreme heat. Suitable contributions may: (i) assess the drivers and underlying processes of extreme heat in observations and/or models; (ii) explore the diverse socio-economic impacts of extreme heat events (for example, on aspects relating to human health or economic productivity); (iii) address forecasting of extreme heat at seasonal to sub-seasonal time scales; (iv) focus on societal adaptation to extreme heat, including the implementation of Heat-Health Early Warning Systems for disaster risk reduction.

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

The session aims to bring together, amongst others, numerical modellers, the observational community and CORDEX-FPS participants, with the aim of advancing understanding of the aforementioned topics. Of particular interest are any 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.

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
-- High-resolution winds and their impacts
-- Convection, energy balance and hydrological cycle including vegetation
-- Model setup and parametrization, including sensitivity to resolution, land surface and dynamics
-- Tropical convection and convective processes at local to regional scale
-- Model evaluation and new evaluation metrics/methods
-- Physical understanding of added value over coarser models
-- Severe storms including supercell thunderstorms and hailstorms
-- The roles of natural and internal variability

Topics related to In-situ observations obtained from aircraft, Uncrewed Aerial Vehicles (UAVs), 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.

Recent extreme weather and climate episodes, including the Canadian heatwave in 2021 and the flooding in Germany in the same summer, 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.

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

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

Solicited Speakers:

- Dr. Fabienne Lohou, Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, France:
" Model and Observation for Surface Atmosphere Interactions (MOSAI) project”.

- Dr. Aaron Boone, CNRM-Université de Toulouse, Météo-France/CNRS, France:
“Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) Project: Overview of the Field Campaign intense phase”.

- Dr. Alexander Baklanov, World Meteorological Organization (WMO), Science and Innovation, Geneva, Switzerland: “Scientific legacy of Sergej Zilitinkevich for boundary layer research and modelling”.

The EU COST action PROBE (Profiling the atmospheric boundary layer at European scale) would like to promote recent advances in profiling the atmospheric boundary layer (ABL) using ground-based remote sensing and instrument networks to facilitate knowledge exchange between all actors concerned with ABL profiling.
We aim at highlighting new developments in measurement technology and advanced products and discussing how new profiling observations will impact various applications like weather, hydrology, climate, air quality, transportations, renewable energy, agriculture, and environmental hazards.
Contributions are welcome from people working with individual ABL profilers (incl. wind, cloud, aerosol, temperature, and humidity) as well as from networks. The session accepts also contributions on advanced products and tools (e.g. clouds and precipitation, forecast indices, fog and icing alerts, aerosols and air quality, wind and turbulence/gusts and ABL characterization) and applications for model assessment, data assimilation, nowcasting, climate simulations, and satellite data validation. Special interest is placed on work reporting on the ABL in specific environments, such as complex terrain, coastal locations, or cities.

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.

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, 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 and precipitation in modulating the cloud-circulation coupling and cloud feedbacks.

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

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

Observations and model simulations illustrate significant ocean variability and associated air-sea interactions in the tropical Atlantic basin from daily-to-decadal time scales. This session is devoted to the understanding of ocean dynamics in the tropical and subtropical Atlantic Ocean, its interaction with the overlying atmosphere from the equator to the mid-latitudes and its climate impacts on adjacent to remote areas. Relevant processes in the ocean include upper and deep ocean circulation, eddies, tropical instability waves, warm pools, cold tongues and eastern boundary upwellings. We are interested in air-sea interactions related to both the seasonal cycle and the development of modes of variability from local to basin scale (e.g. the Meridional Mode, the Atlantic Niño, and the Benguela Niño). We welcome studies on wind variations related to the development of these modes, as well as studies on high-frequency events, such as marine heat waves, the Madden-Julian Oscillation, tropical cyclones and convective systems. Furthermore, we seek studies on climate change in the region, and also of the climatic impacts of change and variability on marine ecosystems. Finally, we are also interested in contributions examining the causes and impacts of systematic model errors in simulating the local to regional Atlantic climate. Studies based on direct observations, reanalysis, reconstructions as well as model simulations are welcome.

Ocean-atmosphere flux exchanges of biogeochemically active constituents have significant impacts on global biogeochemistry and climate. Increasing atmospheric deposition of anthropogenically-derived nutrients (e.g., nitrogen, phosphorus, iron) to the ocean influences marine productivity and has associated impacts on oceanic CO2 uptake, and emissions to the atmosphere of climate active species (e.g., nitrous-oxide (N2O), dimethyl-sulfide (DMS), marine organic compounds and halogenated species). Atmospheric inputs of toxic substances (e.g., lead, mercury, cadmium, copper, persistent organic pollutants) into the ocean are also of concern for their impact on ocean ecosystem health. In recent decades the intensive use of plastics has led to significant levels of persistent micro- and nano- plastics being transported into the marine atmosphere and to the ocean, with considerable uncertainty remaining on transport pathways and oceanic impacts. Other influential recent changes include emission reductions for air pollution abatement which have resulted in changes in cloud and aerosol chemical composition, affecting atmospheric acidity, associated chemical processing and impacts via atmospheric deposition on ocean biogeochemistry.
In turn, oceanic emissions of reactive species and greenhouse gases influence atmospheric chemistry and global climate, and induce potentially important chemistry-climate feedbacks. While advances have been made by laboratory, field, and modelling studies over the past decade, we still lack understanding of many of the physical and biogeochemical processes linking atmospheric deposition of chemicals, nutrient availability, marine biological productivity, trace-gas sources and sinks and the biogeochemical cycles governing air-sea fluxes of these climate active species, as well as on the atmosphere-ocean cycle of microplastics and its impact on the environment and climate.
This session will address the above issues on the atmospheric deposition of nutrients and toxic substances to the ocean, the impacts on ocean biogeochemistry, and also the ocean to atmosphere fluxes of climate active species and potential feedbacks to climate. We welcome new findings from measurement programmes (laboratory, in-situ and remote sensing) and atmospheric and oceanic numerical models.
This session is jointly sponsored by GESAMP Working Group 38 on ‘The Atmospheric Input of Chemicals to the Ocean’, the Surface Ocean-Lower Atmosphere Study (SOLAS).

This session welcomes submissions on new insights into the physical processes at the air-sea interface and their role in ocean-atmosphere exchange of heat, gas, momentum, freshwater, and aerosols.
Presentations based on field or satellite observations, numerical models, or theoretical contributions are welcome.

Examples of processes include solar radiation-induced diurnal warming, rain-induced cool and fresh lenses, and processes controlling the formation and properties of the surface microlayer.
Additional focus is on gustiness associated with convection in the atmospheric boundary layer and evaporative cold pools. Further focus is on air-sea interactions in polar regions, in particular related to cold air outbreaks, including the role of sea ice and the effect of leads. Air-sea interaction related to surface temperature and salinity fronts, as well as oceanic meso- and sub-mesoscale dynamics, are also of great interest. Studies considering the variability of biogeochemical properties related to air-sea processes will also be considered.

The ocean surface mixed layer mediates the transfer of heat, freshwater, momentum and trace gases between atmosphere, sea ice and ocean, thus playing a central role in the dynamics of our climate. This session will focus on the surface mixed layer globally, from the coastal ocean to the deep ocean. We will review recent progress in understanding the key dynamical and biogeochemical processes taking place in the mixed layer: surface waves, Langmuir circulations and turbulence, shear-induced mixing, internal waves, coherent structures, fronts, frontal instabilities, entrainment and detrainment at the mixed layer base, convection, restratification, dynamics of the euphotic layer, carbon and nutrient cycling, etc. The improvement of the representation of surface mixed layer processes in numerical models is a complex and pressing issue: this session will bring together new advances in the representation of mixed layer processes in high resolution numerical models, as well as evaluation of mixed layer properties in climate models using most recent observational datasets. The coupling of the ocean and atmospheric boundary layers as well as the special processes occurring under sea ice and in the marginal sea ice zone will be given special consideration. This session welcomes all contributions related to the study of the oceanic mixed layer independent of the time- and space scales considered. This includes small scale process studies, short-term forecasting of the mixed layer characteristics for operational needs, studies on the variability of the mixed layer from sub-seasonal to multi annual time scales and mixed layer response to external forcing. The use of multiple approaches (coupled numerical modeling, reanalyses, observations) is encouraged.

The rapid decline of the Arctic sea ice in the last decade is a dramatic indicator of climate change. The Arctic sea ice cover is now thinner, weaker and drifts faster. Freak heatwaves are common. On land, the permafrost is dramatically thawing, glaciers are disappearing, and forest fires are raging. The ocean is also changing: the volume of freshwater stored in the Arctic has increased as have the inputs of coastal runoff from Siberia and Greenland and the exchanges with the Atlantic and Pacific Oceans. As the global surface temperature rises, the Arctic Ocean is speculated to become seasonally ice-free by the mid 21st century, which prompts us to revisit our perceptions of the Arctic system as a whole. What could the Arctic Ocean look like in the future? How are the present changes in the Arctic going to affect and be affected by the lower latitudes? What aspects of the changing Arctic should observational, remote sensing and modelling programmes address in priority?

In this session, we invite contributions from a variety of studies on the recent past, present and future Arctic. We encourage submissions examining interactions between the ocean, atmosphere and sea ice, on emerging mechanisms and feedbacks in the Arctic and on how the Arctic influences the global ocean. Submissions taking a cross-disciplinary, system approach and focussing on emerging cryospheric, oceanic and biogeochemical processes and their links with land are particularly welcome.

The session supports the actions of the United Nations Decade of Ocean Science for Sustainable Development (2021-2030) towards addressing challenges for sustainable development in the Arctic and its diverse regions. We aim to promote discussions on the future plans for Arctic Ocean modelling and measurement strategies, and encourages submissions on the results from IPCC CMIP and the recent observational programs, such as the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). This session is cosponsored by the CLIVAR /CliC Northern Ocean Regional Panel (NORP) that aims to facilitate progress and identify scientific opportunities in (sub)Arctic ocean-sea-ice-atmosphere research.

Drs Karen Assmann and Wilken-Jon von Appen are the solicited speakers for the session. Karen Assmann will be presenting on physical and ecological implications of Arctic Atlantification. Wilken-Jon von Appen will be talking about eddies in the Arctic Ocean.

This session is intended to provide an interdisciplinary forum to bring together researchers working in the areas of high-latitude meteorology, atmospheric chemistry, 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 (indicating airmass origins and atmospheric processes); and regional emission and vertical mixing of climate active trace gases and aerosol, such as cloud-forming particles (CCN/INP) and their precursors. It is expected that the recent implementation of new measurements such as those from pan-Arctic water vapor isotope networks, observations such as those obtained during the MOSAiC field program, and data from existing networks will help diagnose long-range moisture and aerosol sources and the coupling between local and large-scale dynamics. 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, 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) 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.

As the most evident example of land use and land-cover change, urban areas play a fundamental role in local to large-scale planetary processes, via modification of heat, moisture, and chemical budgets. With rapid urbanization ramping up globally it is essential to recognize the consequences of landscape conversion to the built environment. Given the capability of cities to serve as first responders to global change, considerable efforts are currently being dedicated across many cities to monitor and understand urban atmospheric dynamics and examine various adaptation and mitigation strategies aimed to offset impacts of rapidly expanding urban environments and influences of large-scale greenhouse gas emissions.

This session solicits submissions from both the observational and modelling communities examining urban atmospheric and landscape dynamics, processes and impacts owing to urban-induced climate change, the efficacy of various strategies to reduce such impacts, and techniques highlighting how cities are already using novel science data and products that facilitate planning and policies on urban adaptation to and mitigation of the effects of climate change. Emerging topics including, but not limited to, compounding impacts with urban COVID-19 outbreaks, citizen science and crowdsourcing, or urban-climate informatics, are highly encouraged.

Aerosol particles are key components of the earth system important in 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 aerosols in the urban atmosphere. By the end of this century 75% of humanity will live in cities. Cities account for >80% of global carbon emissions and have begun to make ambitious commitments, including decarbonisation of multiple sectors. However, over 90% of the world’s population currently breathe dangerously polluted air, with a need to understand the sources, processes and sinks that dictate the properties of aerosol particles in urban environments and the impact they have. We thus invite submissions that fall within this topic that could include sectoral contributions, the indoor/outdoor interface, differential toxicity, projections of future climate impacts etc.

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

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

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.

Anthropogenic aerosol plays a key role in driving climate anomalies over a range of spatial and temporal scales, both near the emission location and remotely through teleconnections. Aerosols can interact with radiation and clouds, directly and through absorption, microphysics and circulation, and thereby modify the surface and atmospheric energy balance, cloud dynamics and precipitation patterns, and the atmospheric and oceanic circulation. This session addresses progress in understanding the mechanisms and pathways by which aerosols affect regional climate features, overall, over the historical era, and in the near future. We encourage contributions on new 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 interplay with modes of variability such as the NAO, AMV, and PDO. Focus studies on monsoon, midlatitude, and Arctic responses, extreme precipitation, circulation changes, daily variability, CMIP6 projections of high and low aerosol futures, and investigations using large ensemble simulations are welcome.

Chemistry and aerosols play a major role in determining surface air quality, the Earth’s energy budget, and climate change. Conversely, climate change affects atmospheric abundances of trace gases and aerosols through composition-climate interactions. This session focuses on global scale atmospheric chemistry and aerosol modelling, radiative forcing, and climate change through the historical period and into the future.
A better understanding of the role of natural aerosols in the atmosphere is essential for assessing climate changes. Our session explores primary aerosols and those formed from precursor gases emitted by natural sources, e.g. from wildfires, deserts, volcanoes, oceans, and vegetation. The session intends to bring together experts from different fields to assess the state-of-the-science knowledge on natural aerosols and to identify future directions to reduce uncertainty in their emissions and impacts. We encourage submissions that use models across different spatial scales and consider past, present or future perspectives, as well as measurements from remote sensing, field campaigns and laboratory experiments.

In particular, it aims to bring together scientists with an interest in:

1. Evaluating reactive gases and aerosols in models against observations

2. Quantifying the impact of emissions changes on atmospheric composition

3. Exploring chemistry-climate interactions in models, with a focus on climate feedbacks involving trace gases and aerosols

4. Quantifying radiative forcing and the climate response to changes in trace gas and aerosol concentrations

5. Distinguishing between truly natural aerosols and those whose emissions or formation are influenced by anthropogenic activities

6. Missing links in our understanding of the lifecycle of natural aerosols

7. The time evolution of contributions of natural aerosols to atmospheric composition and deposition
8. The consequences of changes in natural aerosols


The session welcomes contributions from those currently involved in analysis of recent and ongoing CMIP6 experiments focusing on the areas above,

Anthropogenic emissions of greenhouse gases and ozone depleting substances have caused substantial changes in the chemical composition of the middle atmosphere that, in turn, can influence tropospheric processes. Increasing greenhouse gas levels are expected to modify the stratospheric amount of key radiatively active gases, such as water vapor, ozone and stratospheric aerosols through changes in the stratospheric Brewer-Dobson circulation (BDC). Changes in stratospheric ozone can in turn affect the biosphere (via e.g. changes in UV exposure) and feed back on surface climate via their influence on Earth's radiative budget. In addition, long-term changes in the ozone layer (e.g. ozone hole and recovery) are known to influence the tropospheric circulation and may be further coupled to a variety of Earth system feedbacks, which are to date poorly understood.


We welcome abstracts which explore composition changes and resulting radiative impacts and feedbacks on the tropospheric and stratospheric circulation as well as on surface weather and climate. Abstracts may address these issues on time-scales encompassing inter-annual to centennial timescales as well as impacts ranging from the tropics to poles. In particular, new studies on the influence of stratospheric ozone and composition on weather and climate are of interest. Research might also concern long-term ozone trends (depletion and recovery), as well as water vapor changes and volcanic aerosol impact in the stratosphere. We welcome contributions using chemistry-climate and Earth system models such as the new Chemistry Climate Model Initiative (CCMI-2) and Coupled Model Intercomparison Project (CMIP6), observations, as well as contributions using novel statistical approaches (e.g. Machine, causal inference) to gain insights into composition changes, related feedbacks and theoretical studies.

The composition of the upper troposphere and the lower stratosphere (UTLS) plays a key role in the climate system. Our understanding of the interactions between dynamics, chemistry and climate in this region is rapidly advancing thanks to both observational and modelling studies. In this session we invite studies of dynamical, transport and chemical processes determining the variability and long-term trends in the composition of the UTLS, and related impacts on radiation and dynamics. This particularly includes studies of upper and middle stratospheric as well as of tropospheric dynamics and chemistry affecting the UTLS. We encourage studies bringing together recent in situ and/or remote sensing observations and model simulations of different complexity (e.g., comprehensive climate models, chemistry transport models, idealized and conceptual models).

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. Special emphasis is put on the scientific value of high-quality long-term measurement data sets and supporting model simulations, though the elements related to emerging data sources, 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.

The interactions between aerosols, climate, and weather 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. 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 CL, AS, 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) any study using dust as a (paleo-)climate indicator, including sediment archives in loess, ice cores, lake sediments, ocean sediments and dunes.

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

Methane is an important greenhouse gas that has contributed ∼25% of the radiative forcing experienced to date. Despite methane’s short atmospheric lifetime (~10 years), the global methane mole fraction has increased three times faster than carbon dioxide since 1750. Methane emission mitigation is an effective way to reduce the short-term rate of warming, and is essential to IPCC pathways that limit warming below 2 C. In contrast to carbon dioxide, anthropogenic methane emissions originate from a large variety and number of diffuse point sources that are mostly independent of combustion processes. As a result, systematic, international atmospheric measurements are needed to inform emission inventories and mitigation strategies.

This session will highlight field research and satellite studies that focus on methane emissions from human activities (e.g., oil and gas production, coal mining, fire, rice production, ruminants, landfills and waste). Particular emphasis is on atmospheric observations at different spatio-temporal scales with the aim to (1) reduce the uncertainty in the measured magnitude of emissions, (2) identify source-specific emission patterns and mitigation opportunities, and (3) inform government, industry, and other stakeholders on mitigation pathways.

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.

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

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

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

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

The large uncertainty associated with regional and global anthropogenic climate change is deeply rooted in our limited understanding of molecular scale processes occurring in aerosol particles and cloud droplets, which ultimately affect cloud properties and their climate impacts via modulating particle formation and growth. Atomistic scale properties of single aerosol particles, their interactions with the surrounding vapour phase molecules as well as transport processes within the particle phase typically occur on temporal and spatial scales which are attainable only by a handful of techniques. Molecular simulations (molecular dynamics and Monte Carlo) and single molecule experiments are promising methods with uniquely high spatial and temporal resolution which can complement traditional experimental and modelling approaches. Their recent emergence as tools to characterise molecular scale properties is catalysing the development of a new interdisciplinary field at the interface of molecular modelling and aerosol science, which can help address long-standing problems in new particle formation, gas-to-particle partitioning and heterogeneous nucleation. We welcome  nanoscale observations of processes involving aerosol particles that are based on experiments, molecular simulations or theoretical modelling. We solicit contributions addressing single particle properties of aerosols: single particle structure, thermodynamic properties, dynamic processes in single particles (particle formation and growth, water uptake, adsorption, ice nucleation, bulk transport phenomena, reactivity).

Atmospheric aerosol-cloud-climate interactions (e.g. heterogeneous nucleation, particle oxidation and photosensitization, molecular composition-, phase-, acidity- and structure- changes, ...) are fundamental processes in the atmosphere. Despite the importance of these processes in energy transfer, cloud dynamics, precipitation formation, and hence in climate change, little is known about the molecular mechanism and the respective contribution of different structural and chemical surface properties of the atmospheric aerosols controlling these processes in the atmosphere. For Example, ice particles in the atmosphere, both in cirrus and mixed-phase clouds, contribute to the largest uncertainty in interpretations of the Earth’s changing energy budget. Their large variability in number, size, shape, and surface properties makes it difficult to understand and parameterize their microphysical and hence radiative properties.

Fundamental understanding of the cloud dynamics and aerosol properties, which play the major role in the climate system, will require the understanding of gas-, water-, and ice-aerosol surface interactions. To advance our knowledge about atmospheric processes, this session aims to bring together two research areas, namely (1) Atmospheric Surface Science (ASS) and (2) Ice Nucleating Particles (INP):
(1) ASS is concerned with the experimental and theoretical approaches investigating atmospheric interactions as well as ice nucleation processes “on the molecular level”. The goal is to fill the gap between the large-scale atmospheric processes and gas-, water-, and ice- interactions with atmospherically relevant mineral and biological surfaces.
(2) INP are concerned with the laboratory examination, on a fundamental level, trying to understand the nucleation processes and characterizing INP in the atmosphere.

The dominant species of absorbing aerosols (AA) in the atmosphere are mineral dust (DU) and light-absorbing carbonaceous aerosols, which include black carbon (BC) and the absorbing component of organic aerosol, referred to as brown carbon (BrC). AA emissions (from deserts, biomass burning, biogenic sources, and anthropogenic activities) cover vast regions of the earth and directly modify surface fluxes, heating profiles and cloud properties. The role of AA in the earth system remains uncertain and can be attributed to all aspects of the aerosol lifetime including emission processes, optical properties, evolution, and their interaction with (and influence on) radiation, clouds, dynamics, and precipitation processes.

Reducing these uncertainties requires working across all scales, from measuring individual particles, to observing continental scale perturbations, and ultimately representing them in our earth system models. This session aims to bring together research from across all of these scales. We welcome presentations covering, but not restricted to, the following topics:

General:
• Global impacts of AA
• AA emission inventories and processes
• Regional / large-scale influences of AA
• Above-cloud impacts of AA
• Role of AA in aerosol-cloud interactions
• AA in the upper troposphere
• Global climatologies of BC, BrC, and DU
• Remote-sensing of AA
Focused:
• Ageing of all AA species: BC, BrC, and DU
• Impacts of absorption on self-lofting
• Coarse mode dust in the atmosphere and models
• Source-dependent dust optical properties
• BC ageing enhancement / mixing state / morphology in climate models
• The role of particle-to-particle variability / heterogeneity
• BrC spectral dependence
• Global constraints on BrC radiative forcing
• Absorption properties of biogenic aerosols
• Constraining absorption using observations

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.