In this session we celebrate the 2025 awardees of the Atmospheric Sciences division through the Vilhelm Bjerknes Medal Lecture by Ulrike Lohmann and the Atmospheric Sciences Division Outstanding ECS Award Lecture by Dominik Stolzenburg.

This session explores advancements in understanding and forecasting the weather, focusing on severe weather phenomena such as moist convection and Mei-yu frontal systems. It integrates AI methods, numerical modelling with particular attention to moist-convective models with intermediate complexity, e.g. Aeolus 2.0 & mcTRSW models, and observational techniques to enhance forecasting accuracy. Key topics include AI-based weather forecasting, ensemble prediction, mesoscale models, AI-driven nowcasting, post-processing, blending, verification and remote sensing technologies. The session also delves into the dynamics of moist convection, cloud formation, precipitation patterns, and their relationship with extreme weather and climate change. A segment on Mei-yu frontal systems highlights field experiments, cloud microphysics, and model improvements for better precipitation forecasts. The session fosters interdisciplinary discussions on breakthroughs and challenges in weather science.

This session welcomes papers on:

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

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

3) Development and improvement of model physics - progress in research on advanced model physics parameterization 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 parameterization, and radiation);

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

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

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

7) Advances and challenges in applying data from various conventional and avant-garde observation platforms to evaluate and improve high-resolution simulations and forecasting.

High-impact weather events, such as extreme rainfall, severe storms, damaging winds, landfalling atmospheric rivers, hurricanes/typhoons, heatwaves, and droughts, have significant impacts on our society and daily life. Data assimilation (including AI applications for data assimilation) and Research to Operations (R2O) play a crucial role in enhancing forecasts for high-impact weather events. This session will focus on recent research and advancements in atmospheric data assimilation, AI for data assimilation, and Research to Operations (R2O) aimed at improving forecasts for high-impact weather events, particularly those intended for operational and impact-oriented applications. We encourage submissions that explore various topics, such as advancements in data assimilation algorithms/techniques/systems, enhanced data preprocessing, assimilation of novel observation types, observational impact studies, synergies between artificial intelligence (machine learning) and data assimilation, Research to Operations (R2O) activities, the verification and validation of forecasts against theoretical frameworks and observational data, and other relevant studies.

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.

This session invites contributions from developments in

• Convective-scale data assimilation techniques
• Use of machine learning in convective scale data assimilation
• Applications of machine learning to forecasting on convective scales
• Convective-scale model and observation uncertainty representation
• Ensembles and uncertainty quantification using machine learning
• Advances in convective-scale modeling and parameter estimation
• Assimilation of ground and space-based radar data
• Active and passive satellite data assimilation
• Assessment of the impact of convective-scale data assimilation on global and regional prediction
• Observation operators for remote sensing and data assimilation
• Observations at convective scales: new observing technologies and strategies

In recent years, machine learning (ML) and artificial intelligence (AI) have emerged as powerful tools for weather forecasting and detection of extreme weather and climate events. The application of data-driven algorithms across different temporal and spatial scales has shown great promise in predicting phenomena such as hurricanes, floods, heatwaves, and droughts and improving the accuracy and timeliness of climate projections.



This session seeks contributions exploring the development and application of ML or ML-enhanced algorithms for forecasting weather and climate at multiple timescales and for detecting and forecasting extreme weather and climate events. We encourage submissions that address the use of AI for meteorological forecasts, extended-range forecasts, sub-seasonal to seasonal climate forecasts, or longer-term climate projections, spanning local to global spatial scales. We also welcome studies that integrate ML with physical mechanisms, leading to AI-driven advancements that improve the representation of climate variables in numerical models or climate datasets.

By bringing together experts from AI, data science, meteorology, and climate science, this session aims to foster interdisciplinary collaborations that push the boundaries of weather and climate forecasting and understanding extreme weather and climate events. We encourage submissions from early-career scientists, established researchers, and industry professionals alike.

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

(a) Modes of variability (e.g. Madden Julian Oscillation (MJO) and others) impacting the S2S predictability;
(b) Tropical/extratropical wave dynamics and their effects on weather patterns;
(c) Teleconnections and combined influence of climate variability modes;
(d) The role of the atmosphere, ocean, land, and ice processes in S2S predictability;
(e) Predictability and predictive skill of atmospheric or surface variables, and other variables relevant for socio-economic sectors, such as sea ice, snow cover, soil moisture, and land surface;
(f) Use of AI/ML methods for S2S prediction, data-driven models, post-processing, and attribution, including innovative techniques for improving forecast accuracy;
(g) Case studies of extreme or high-impact event prediction on the S2S timescale;
(h) Sector-specific applications, impact studies, and climate services on the S2S timescale, including integration of S2S predictions into decision support systems at local, regional, or global levels and co-production of knowledge with stake-holders and decision-makers;
(i) Evaluation and improvement of S2S prediction systems, including advancements in model physics and comparison between dynamical and data-driven prediction models, data assimilation, ensemble forecasting, and initialization techniques.

Weather is chaotic, with strong sensitivity to initial conditions tied to the intrinsic limit to predictability. The strong sensitivity also suggests effective control in which small modifications to the atmospheric conditions grow rapidly and result in big changes. Weather predictability has been studied extensively in the past decades, and the weather prediction skills have been improving consistently. Now with the accurate weather prediction, we are ready to study weather controllability, the other side of a coin. Control is achieved by effective accumulation and combination of modifications or interventions like an orbit control of spacecraft. This session welcomes presentations about understanding of weather sensitivity and predictability, theoretical developments of controllability beyond predictability, weather modification techniques, and other related topics toward weather controllability.

This session covers climate predictions from seasonal to multi-decadal timescales and their applications. Continuing to improve such predictions is of major importance to society. The session embraces advances in our understanding of the origins of seasonal to decadal predictability and of the limitations of such predictions. This includes advances in improving forecast skill and reliability and making the most of this information by developing and evaluating new applications and climate services.
The session welcomes contributions from dynamical models, machine-learning or other statistical methods and hybrid approaches. It will investigate predictions of various climate phenomena, including extremes, from global to regional scales, and from seasonal to multi-decadal timescales (including seamless predictions). Physical processes and sources relevant to long-term predictability (e.g. ocean, cryosphere, or land) as well as predicting large-scale atmospheric circulation anomalies associated with teleconnections will be discussed. Analysis of predictions in a multi-model framework, and ensemble forecast initialization and generation will be another focus of the session. We are also interested in approaches addressing initialization shocks and drifts. The session welcomes work on innovative methods of quality assessment and verification of climate predictions. We also invite contributions on the use of seasonal-to-decadal predictions for risk assessment, adaptation and further applications.

This session welcomes contributions on atmospheric convection, including dry, shallow, or deep convection. A particular session focus is the organization of convection, such as mesoscale convective systems, convectively-coupled waves, idealized studies of self-aggregation, or research on the importance of organization for climate sensitivity. Additionally, submissions that address other aspects of convection like the convective lifecycle and structures including cold pools, interactions of convection with other physical processes or the representation of convection in numerical weather prediction and climate models are strongly encouraged. The research can use any tool, from idealized theoretical models, large-eddy simulations, convection-permitting simulations, to coarser-resolution simulations using parameterised convection, machine learning techniques, or observations and field campaigns.

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.

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

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

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

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

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

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

Lightning is the energetic manifestation of electrical breakdown in the atmosphere, occurring as a result of charge separation processes operating on micro and macro-scales, leading to strong electric fields within thunderstorms. Lightning is associated with tropical storms and severe weather, torrential rains and flash floods. Lightning is also responsible for a vast number of wildfires, burned area, and fire emissions to the atmosphere. It has significant effects on various atmospheric layers and drives the fair-weather electric field. It is a strong indicator of convective processes on regional and global scales, potentially associated with climate change. Lightning produces nitrogen oxides, which are a precursor to ozone production. Thunderstorms and lightning are essential parts of the Global Electrical Circuit (GEC) and control the fair weather electric field. They are also associated with the production of energetic radiation up to tens of MeV on time scales from sub-millisecond (Terrestrial Gamma-ray Flashes) to tens of seconds (gamma-ray glows).

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

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

The statistical characterization and modelling of precipitation are crucial in a variety of applications, such as flood forecasting, water resource assessments, evaluation of climate change impacts, infrastructure design, and hydrological modelling. This session aims to gather contributions on research, advanced applications, and future needs in the understanding and modelling of precipitation, including its variability at different scales and its sources of uncertainty.

Contributions focusing on one or more of the following issues are particularly welcome:
- Process conceptualization and approaches to modelling precipitation at different spatial and temporal scales, including model parameter identification, calibration and regionalisation, and sensitivity analyses to parameterization and scales of process representation.
- Novel studies aimed at the assessment and representation of different sources of uncertainty of precipitation, including natural climate variability and changes caused by global warming.
- Uncertainty and variability in spatially and temporally heterogeneous multi-source ground-based, remotely sensed, and model-derived precipitation products.
- Estimation of precipitation variability and uncertainty at ungauged sites.
- Modelling, forecasting and nowcasting approaches based on ensemble simulations for synthetic representation of precipitation variability and uncertainty.
- Scaling and scale invariance properties of precipitation fields in space and/or in time.
- Dynamical and statistical downscaling approaches to generate precipitation at fine spatial and temporal scales from coarse-scale information from meteorological and climate models.

Rainfall is a “collective” phenomenon emerging from numerous drops. It reaches the ground surface with varying intensity, drop size and velocity distribution. Understanding the relation between the physics of individual drops and that of a population of drops remains an open challenge, both scientifically and for practical implications. This remains true also for solid precipitation. Hence, it is much needed to better understand small scale space-time 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. Similarly to the small scales, accurate measurement and prediction of the spate-time distribution of precipitation at hydrologically relevant scales still remains an open challenge.

This session brings 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 encouraged:
- 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;
- Drop (or particle) size distributions, small scale variability of precipitation, and their 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.
- Rainfall simulators developed to investigate the accuracy of disdrometer measurements in assessing drop size and fall velocity.

Precipitation, both liquid and solid, is central to the global water/energy cycle through its coupling of clouds, water vapor, atmospheric motion, ocean circulation, and land surface processes. While precipitation is the primary source of freshwater, it also has tremendous socio-economic impacts associated with extreme weather events such as hurricanes, floods, droughts, and landslides. Knowledge of precipitation characteristics from local to 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:
1. 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.
2. Precipitation climatologies at regional to global scales; areal distribution of measured precipitation; classification of precipitation patterns; spatial and temporal characteristics of precipitation; methodologies adopted and their uncertainties; comparative studies.
3. Remote sensing of precipitation (spaceborne, airborne, ground-based, underwater, or shipborne sensors) and retrieval techniques; 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.
4. Contributions to current and future missions, such as the international Global Precipitation Measurement (GPM) mission, Atmospheric Observing System (AOS), EUMETSAT Polar System-Second Generation (EPS-SG), Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS), Arctic Weather Satellite (AWS), Earth Clouds, Aerosol and Radiation Explorer (EarthCARE), tomorrow.io constellation and the Advanced Microwave Scanning Radiometer-3 (AMSR-3).

Snow cover characteristics (e.g., spatial distribution, surface and internal physical properties) are continuously evolving over a wide range of scales due to meteorological conditions, such as precipitation, wind, and radiation.
Most processes occurring in the snow cover depend on the vertical and horizontal distribution of its physical properties, which are primarily controlled by the microstructure of snow (e.g., density and specific surface area). In turn, snow metamorphism changes the microstructure, leading to feedback loops that affect the snow cover on coarser scales. This can have far-reaching implications for a wide range of applications, including snow hydrology, weather forecasting, climate modelling, avalanche hazard forecasting, and the remote sensing of snow. The characterization of snow thus demands synergetic investigations of the hierarchy of processes across the scales, ranging from explicit microstructure-based studies to sub-grid parameterizations for unresolved processes in large-scale phenomena (e.g., albedo and drifting snow).
This session is therefore devoted to modelling and measuring snow processes across scales. The aim is to gather researchers from various disciplines to share their expertise on snow processes in seasonal and perennial snowpacks. We invite contributions ranging from “small” scales, as encountered in microstructure studies, over “intermediate” scales typically relevant for 1D snowpack models, up to “coarse” scales, that typically emerge for spatially distributed modelling over mountainous or polar snow- and ice-covered regions. Specifically, we welcome contributions reporting results from field, laboratory, and numerical studies of the physical and chemical evolution of snowpacks. We also welcome contributions reporting statistical or dynamic downscaling methods of atmospheric driving data, assimilation of in-situ and remotely sensed observations, representation of sub-grid processes in coarse-scale models, and evaluation of model performance and associated uncertainties.

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

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

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

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

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

We invite studies

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

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

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

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

* using the isotopic fingerprint of atmospheric processes and weather systems to obtain new mechanistic insights into changes in the water cycle;

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

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

The understanding of tropical phenomena and their representation in numerical models still raise important scientific and technical questions, particularly in the coupling between the dynamics and diabatic processes. Among these phenomena, tropical cyclones (TC) are of critical interest because of their societal impacts and because of uncertainties in how their characteristics (cyclogenesis processes, occurrence, intensity, latitudinal extension, translation speed) will change in the framework of global climate change. The monitoring of TCs, their forecasts at short to medium ranges, and the prediction of TC activity at extended range (15-30 days) and seasonal range are also of great societal interest.
The aim of the session is to promote discussions between scientists focusing on the physics and dynamics of tropical phenomena. This session is thus open to contributions on all aspects of tropical meteorology between the convective and planetary scale, such as:

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

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

Findings from recent field campaigns are also encouraged.

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

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

This session invites presentations on any aspects of monsoon research in present-day, future and palaeoclimate periods, involving observations, modelling, attribution, prediction and climate projection. Topics ranging from theoretical works based on idealized planets and ITCZ frameworks to the latest field campaign results are equally welcomed, as is work on impacts, extremes, NWP modelling, S2S and decadal forecasting, and the latest CMIP6 findings to help inform the IPCC AR7. Applications of AI/ML to monsoon studies are also encouraged.

The large-scale atmospheric circulation is an essential component of the climate system. Understanding the drivers, variability and the dynamical processes of this circulation is important for improving future projection of global and regional circulation patterns under anthropogenic climate change, and for predicting the associated impacts on extreme weather and climate events.

This session encourages contributions covering various theoretical and practical aspects of the large-scale atmospheric circulation, including but not limited to the following topics:
· The response of the large-scale atmospheric circulation to climate change, including latitudinal shifts of the jet stream and the Hadley cell subtropical edge.
· Changes and trends in storm track intensity and structure in response to climate change, or due to internal variability.
· The representation of the large-scale atmospheric circulation in climate models: inter-model variability, model biases and ways to reduce uncertainty in model projections.
· Novel metrics and analysis methods for studying the large-scale atmospheric circulation, using observational or model data.
· Interactions between the different components of the large-scale circulation, including tropical-extratropical interactions and teleconnection patterns.
· The role of moisture in the large-scale atmospheric circulation.
· Energy transport by the large-scale atmospheric circulation.
· Stratospheric-tropospheric interactions affecting the large-scale circulation.

Rossby wave dynamics stands at the intersection of several open research questions, ranging from our basic understanding of mid-latitude variability to the short- and medium-range predictability of high-impact weather events, and to the circulation changes expected from anthropogenic global warming. Rossby waves exist and propagate along vorticity gradients such as the one related to the tropopause-level jet stream, whose complex meandering often "breaks" leaving the place to nonlinear circulation features, such as atmospheric blocking.

Recent extreme weather and climate episodes, like heavy rainfall events leading to flash floods (e.g. in Germany, Switzerland, Italy and Spain in 2024), recurrent and concurrent summer heatwaves or unforeseen winter cold spells (e.g. in Scandinavia in winter 2023/24), highlight the need to improve our understanding of jet streams and of the associated linear and non-linear, planetary and synoptic-scale Rossby wave dynamics in the atmosphere to better constrain the impacts of Rossby waves on extreme weather and climate events.

Abstracts are invited on a wide range of topics, with a focus on, but not limited to, the following areas:

(1) Theoretical developments in the dry and moist dynamics of Rossby waves, wave breaking, atmospheric blocking, and of jet streams acting as atmospheric Rossby waveguides. This includes the role of local and remote drivers (e.g., the tropics, Arctic, or stratosphere) in affecting Rossby wave evolution.
(2) Linkages between extreme weather/climate events and the jet stream, as well as the associated linear and non-linear Rossby wave evolution during such events, including wave breaking, cut-off formation and re-absorption, and atmospheric blocking.
(3) Application of cutting-edge methods to study the multi-scale interaction of Rossby waves from the convective scale to the large-scale dynamics, and its representation in existing weather and climate models (e.g. hierarchical and/or high-resolution modelling, machine learning/AI-based approaches).
(4) Exploring the effect of Rossby wave packets on predictability at lead times from medium range (~2 weeks) to seasonal time-scales. This includes the potential role of blocking and of teleconnections involving Rossby wave propagation.
(5) Projected future changes in planetary or synoptic-scale Rossby waves, or in their future connection to weather and climate events.

This session investigates mid-latitude cyclones and storms on both hemispheres. We invite studies considering cyclones in all different stages of their life cycles, from initial generation to the final development, including studies to large- and synoptic-scale conditions influencing cyclones’ growth to a severe storm, their dissipation, and related socioeconomic impacts.
Papers are welcome, which focus also on the diagnostic of observed past and recent trends, long- and short-term natural variability, as well as on future storm development under changed climate conditions. This will include storm predictability studies on different time and spatial scales. The session also invites studies investigating storm related impacts: Papers are welcome dealing with vulnerability, diagnostics of sensitive social and infrastructural categories and affected areas of risk for property damages and loss. Which novel risk transfer mechanisms are currently developed or used? Which novel mechanisms (e.g., adapted re-insurance products) are already implemented or will be developed in order to adapt to future loss expectations under anthropogenic climate change?

Large-scale atmospheric dynamics and synoptic systems are key drivers of near-surface variables (e.g. air temperature, precipitation), their variability and their extremes such as heatwaves, floods, and droughts. Recent regional extreme weather events (e.g. floods and heatwave in Europe in September 2023) underline the need to further study the link between regional extremes and features of the large-scale atmospheric circulation (e.g., circulation patterns, weather regimes, blocking patterns, extra-tropical cyclones, teleconnection indices). Various linear and non-linear approaches of synoptic climatology (e.g., multiple regression, canonical correlation, neural networks) can be applied to relate the circulation dynamics to diverse climatic and environmental elements and extremes. This session focuses on understanding regional extremes, their link to atmospheric dynamics, and their future evolution under climate change while welcoming contributions from various methodological approaches.

We welcome contributions that explore:
- The links between large-scale atmospheric circulation features (e.g., circulation patterns, weather regimes, blocking patterns, extra-tropical cyclones, teleconnection indices, NAO) and various types of regional extreme weather events (such as heat waves, heavy precipitation, floods, droughts)
- Past, recent and future trends in frequency, intensity, and variability of regional extremes or surface environmental variables and their associated atmospheric features under climate change
- The influence of internal climate variability on the occurrence of regional extreme events associated with large-scale atmospheric circulation features
- The use of innovative methods, including large ensembles, and AI for circulation type classification

This session invites contributions that explore the connections between different types of regional extremes and the atmospheric circulation, as well as studies from general synoptic climatology that focus on the relationship between atmospheric circulation dynamics and near surface environmental variables, their variability, and changes. The aim is to enhance our understanding of the dynamic drivers behind regional extremes in the context of climate change.

Atmospheric rivers (ARs) are narrow and transient filaments of intense water vapor transport in the lower troposphere. They account for 90% of poleward moisture transport and drive high-impact weather extremes all around the globe. Future projections suggest that landfalling ARs will become even more hazardous as they further intensify in a warmer climate. Given the fundamental role of ARs in the global water cycle, relevant research is rapidly expanding across different disciplines. With new data sources and novel methodological approaches, the multidisciplinary AR community has been breaking ground and posing fundamental questions for the understanding of AR processes and impacts.

By bringing together experts from diverse disciplines, this session aims to provide a comprehensive platform for discussing the latest advances in AR science. We invite all contributions that aim at a better understanding of AR uncertainties, processes, and impacts across past, present, and future climates. Relevant topics of the session include, but are not limited to:

• Observation, identification, and monitoring of ARs
• Physical, dynamical, & microphysical aspects of ARs
• Aerosol & biochemical aspects of ARs
• Environmental and socioeconomic impacts of AR-induced weather extremes
• ARs as a component of compound events
• AR dynamics and impacts in understudied regions
• Role of ARs in the changing Cryosphere
• Forecasting of ARs
• ARs in past, present, and future climates

The circulation of the stratosphere significantly impacts tropospheric weather and climate. Key phenomena, including the stratospheric polar vortex, the Brewer-Dobson circulation, and the Quasi-Biennial Oscillation, are particularly influential. Variations in these phenomena modulate the propagation of atmospheric waves, exert a dynamical downward influence on the troposphere, and facilitate the transport of climatically important chemical constituents. Understanding, observing, and accurately simulating the dynamics of the stratosphere are therefore essential for predicting changes in tropospheric weather and climate. This session focuses on the causes and consequences of variations in the stratospheric circulation, including its natural and anthropogenic drivers, chemical transport and mixing processes, and its role for the prediction of weather and climate. We welcome abstracts that address these topics from observational, modeling, or theoretical perspectives across all scales.

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

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

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

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

Extreme weather and climate conditions, such as recent events unprecedented in the observational record, have high-impact consequences globally. Some of these events would have been arguably nearly impossible without human-made climate change, and broke records by large margins. Furthermore, compounding hazards and cascading risks are becoming evident. Continuing warming does not only increase the frequency and intensity of events like these, or other until now unprecedented extremes, it also potentially increases the risk of crossing tipping points and triggering abrupt unprecedented impacts. To increase preparedness for high impact climate events, developing novel methods, models and process-understanding that capture these events and their impacts is paramount.

This session aims to bring together the latest research quantifying and understanding high-impact climate events in past, present and future climates. We welcome studies ranging across spatial and temporal scales, and covering compound, cascading, and connected extremes as well as worst-case scenarios and storylines, with the ultimate goal to provide actionable climate information to increase preparedness to such extreme high-impact events.

We invite work addressing high impact extreme events via, but not limited to, observations, model experiments and intercomparisons, climate projections including large ensembles and unseen events, diverse storyline approaches such as event-based or dynamical storylines, insights from paleo archives and attribution studies. We also especially welcome contributions focusing on physical understanding of high-impact events, on their ecological and socioeconomic impacts, as well as on approaches to potentially limit such impacts

The session is sponsored by the World Climate Research Programme lighthouse activity on Understanding High-Risk Events.

The climate system is changing rapidly, with some regions experiencing increases in extreme events beyond what is expected from climate model simulations. To improve the accuracy of climate predictions and projections, it is necessary to (1) identify and explain what factors and processes drive observed and predicted climate changes, (2) critically assess how key processes are represented in climate models, (3) understand and explain the predicted signals, which often result from the interaction of multiple drivers, and (4) use this knowledge to calibrate and further develop predictions to provide more reliable and thus useful information to society. In combination, these research activities contribute to building the capability for an integrated attribution and prediction of climate change - a key goal of the WCRP Lighthouse Activity on Explaining and Predicting Earth System Change (EPESC) and the Horizon-Europe project EXPECT.

Progress in integrated attribution and prediction will benefit from combining diverse data sources, such as Earth Observations, and various climate model experiments, including those at very high resolutions. This session invites contributions on advancing integrated attribution and prediction, with a particular focus on annual to decadal timescales, which involves explaining, predicting and constraining climate changes from regional to global scales. Relevant topics include, for example, studies attributing the drivers of specific climate phenomena and extremes such as the atmospheric circulation during the boreal summer and related surface extremes, evaluating climate responses to different forcings and internal variability, correcting biased climate responses e.g. using process-based constraints, providing calibrated prediction and projections of future climate based on these constraints, and methods that exploit a variety of data in combination with novel analysis techniques including Artificial Intelligence.

A longstanding pursuit in climate science is to better understand Earth’s climate sensitivity, which
quantifies how global mean surface temperature responds to changes in radiative forcing. Uncertainty
in climate sensitivity arises primarily due to uncertainty in radiative feedbacks, which can be influenced
by a large range of processes including cloud microphysics, large-scale circulation of the atmosphere and
ocean, or the pattern of surface temperature changes. This session solicits work on theory, modeling,
and observations related to Earth’s climate sensitivity, with a particular focus on recent advances in
understanding the causes and impacts of the surface temperature pattern effect. The pattern effect
describes how surface temperature changes with identical global mean values can have hugely different
effects on the radiation budget depending on their spatial distribution, having significant implications
for interpreting temperature changes from observations, paleo-climate proxies, and climate-change
projections.
We welcome contributions related, but not limited, to:
• Radiative feedbacks and their modulation by surface warming patterns
• Air-sea interactions and ocean dynamics relevant to surface temperature patterns
• Process studies of feedbacks from clouds and moist processes
• Ocean heat uptake and transient climate sensitivity
• Theoretical models of climate sensitivity
• Interbasin interactions and teleconnections spanning scales from sub-basin to global
This session serves as an exchange platform for the often more separated ocean and atmosphere communities, and we especially encourage contributions from the ocean community.

The climate system exhibits complex variability across different timescales. Part of this complexity is influenced by the teleconnections, recurring patterns in the atmosphere and ocean that strongly shape the regional climate variability and climate change. However, given the large internal variability and strong external forcings involved, understanding the role of teleconnections in climate variability and change remains challenging. Statistical, dynamical and modelling approaches have provided many insights to date. More recently, the integration of these approaches has developed rapidly, and new data-driven approaches are becoming widespread. This session aims to bring together researchers using any combination of these approaches to explore climate variability, teleconnections across timescales from synoptic scale to long-term change, and in particular, how variability on different timescales is connected. The physical explainability and interpretability of statistical and modelling results as well as the accurate and appropriate use of statistics in physics-centred research are a focus of the session.
We invite contributions that address one or more of the following topics: disentangling variability in teleconnections and their influence on regional climate, dynamics and predictive potential of teleconnections, the influence of large-scale changes in driving future regional climate change, understanding model-observation discrepancies in climate variability and teleconnections.
Studies that employ innovative approaches to bridge statistical analysis and physical understanding are particularly encouraged, including but not limited to machine learning techniques, causal inference methods, storyline approaches, Bayesian methods, and novel diagnostics for teleconnections.

Mountains cover approximately one-quarter of the total land surface on the planet, and a significant fraction of the world’s population lives within, in their vicinity, and downstream. 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. This session is devoted to showcasing research that contributes to improving our 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. This includes the interaction of mountain weather and climate with the terrestrial cryosphere.

We welcome contributions describing the influence of mountains on the atmosphere on meteorological and climate time scales, including terrain-induced airflow, orographic gravity waves, 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.
We also encourage theoretical, modeling and observational studies on orographic gravity waves and their effects on the weather and the climate.

Furthermore, we invite studies that investigate climate processes and climate change in mountain areas based on monitoring and modeling activities. Particularly welcomed are contributions that connect with and address the interdisciplinary objectives of the Elevation-Dependent Climate Change (EDCC) working group of the Mountain Research Initiative ( https://mountainresearchinitiative.org/our-activities/community-led-activities/active-working-groups/elevation-dependent-climate-change/).

Renewable energy has become new sources of electrical power. By their very nature, wind, solar, 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, forests, or coastal and 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, including, but not limited to:
• Wind conditions (both resources, siting conditions and loads) on short and long time scales for wind power development, in different environments (e.g. mountains, forests, coastal, offshore or urban).
• Offshore wind development: interaction between atmosphere, sea and wind turbine/wind farms, for both bottom-fixed and floating wind, and its impact on marine environment
• Long term analysis of inter-annual variability of solar and wind resource
• Typical Meteorological Year and probability of exceedance for wind and solar power development
• Wind and solar resource and atlases
• Wake effect models and measurements, especially for large wind farms and offshore
• Performance and uncertainties of forecasts of renewable power at different time horizons and in different external conditions.
• Forecast of extreme wind events and wind ramps
• Local, regional and global impacts of renewable energy power plants or of large-scale integration.
• Dedicated wind measurement techniques (SODARS, LIDARS, UAVs, Satellite etc.)
• Dedicated solar measurement techniques from ground-based and space-borne remote sensing
• Tools for urban area renewable energy supply strategic planning and control
• AI and Machine Learning approaches for weather forecasting and its applications

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

Session aims to delve into the world of fog and dew, exploring the scientific processes governing their formation, interaction and environmental impact. It will also showcase cutting-edge research across disciplines. The session will cover a wide range of topics, including the following Fog Types and Processes:
Classifications of fog, conditions that lead to fog formation and complex processes that govern fog life cycles, the influence of synoptic systems on fog formation.
Boundary Layer Processes include understanding how factors like temperature inversions, wind, near-surface processes like the Ramdas layer, and stability contribute to fog formation.
Turbulence and Aerosols Role of turbulence in mixing and impact on fog. Additionally, role of aerosols on fog droplet formation and numerical studies on fog-turbulence and fog-aerosol interactions.
Detection and Forecasting
Advancements in satellite remote sensing to detect and characterise fog.
Importance of observation networks and field experiments for fog study.
Capabilities and limitations of NWP models in forecasting fog. Advancements in high-resolution models and parameterisation; specific studies like DNS or LES.
Challenges and opportunities in incorporating real-time observations via data assimilation and potential of AI and ML techniques to improve forecasting.
Fog and Environmental Interactions
Examination of the relationship between fog/dew and air pollution, like fog as a sink for pollutants but aids formation of secondary pollutants through chemical reactions. Mitigation strategies to address the combined impacts of fog/dew and air pollution. Moreover, studies covering fog/dew chemistry will be covered under this topic.
Microphysical and Surface Processes: Fundamental physics governing fog and dew formation, radiative cooling, vapor pressure deficit, and surface properties that influence these processes. The role of land surface characteristics, such as soil moisture, vegetation cover, and heat fluxes in fog formation or dewfall. Moreover recent advancements in surface energy balance models.
Applications Fog and dew harvesting techniques, passive collection methods using specialised meshes. Significance of these techniques in water-scarce regions and their efficiency.
The session will deepen the understanding of fog and dew, paving the way for future advancements in research, forecasting, and potential applications.
Co-sponsored by the International Fog and Dew Association (IFDA) and iLEAPS.

The session invites experimentalists and modelers working on air-land interactions from local to regional scales, in vegetated and/or urban systems. The program is open to a wide range of innovative studies in micrometeorology and related atmospheric and remote sensing disciplines. The topics may include the development of new observational devices, measurement techniques, experimental designs, data analysis methods, as well as novel findings on surface layer theory and parametrization, including local and non-local processes. Theory-based contributions may encompass soil-vegetation-atmosphere transport, internal boundary-layer theories, and flux footprint analyses. Of particular interest are synergistic studies employing experimental data, parametrizations, and models addressing energy and trace gas fluxes (of inert and reactive species) as well as water, carbon dioxide and other GHG fluxes. We focus on addressing 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, coupling/decoupling, stable stratification and night time fluxes, dynamic interactions with atmosphere, and plants (in canopy and above canopy) and soils.

Ocean-atmosphere chemical flux exchanges have significant impacts on global biogeochemistry and climate. This session focuses on new research in the following areas: air-sea fluxes of greenhouse gases (e.g., CO2, CH4, N2O), atmospheric deposition of nutrients (e.g., nitrogen, phosphorus, iron) and its impact on ocean biological systems, the influence of ocean emissions of reactive gases and aerosols on atmospheric chemistry and climate (e.g., dimethyl-sulfide (DMS), marine organic compounds, halogenated species), and on the important biogeochemistry-climate feedback loops in the ocean-atmosphere system as well as future changes in these fluxes in response to anthropogenic and climate stressors. The session has long-standing links to the Surface Ocean Lower Atmosphere Study (SOLAS; https://www.solas-int.org/) and GESAMP Working Group 38 on atmospheric input of chemicals to the ocean (http://www.gesamp.org/work/groups/38). We welcome submissions from all remit areas of these programs, and from a range of analysis approaches: field measurements, remote sensing, laboratory studies, and atmospheric and oceanic numerical models.

This year we particularly welcome contributions on the following specialist themes:
(a) greenhouse gas emissions and cycling from coastal zones, with particular focus on the impacts of nutrient and pollutant transport across the land-ocean continuum (e.g. via riverine input, glacier meltwater runoff, submarine groundwater discharge), as well as benthic-pelagic coupling for greenhouse gas budgets in regional and global scales; and
(b) the role of the Sea-Surface Microlayer (SML) as a biofilm environment and direct air-sea- interface, and its influence on deposition and emission fluxes of gases, aerosols, and particulates between the ocean and atmosphere.

Covering 70% of the Earth's surface, the sea surface microlayer (SML) is recognized as a critical boundary between the ocean and atmosphere. Its unique position places the SML at the center of various global processes in biogeochemistry and climate science. This session welcomes recent advancements in understanding the SML's distinctive chemical, biological, and physical characteristics, with a focus on understanding the underlying mechanisms of processes. Particular emphasis is given to the SML's function in modulating air-sea exchanges of heat, freshwater, gases, particles, and biota, but also exchange processes between the SML and the underlying bulk water, which are crucial for a more comprehensive understanding.. The concept of the SML as a biogeochemical reactor is also a central theme in the session to highlight the roles of environmental interfaces in marine biogeochemistry. Of further interest is the accumulation of pollutants such as hydrocarbons, microplastics, soot and pharmaceuticals, but also pathogenic microorganisms and viruses. In this context, the formation of (bio)aerosols as well as deposition processes play a role. To advance future studies, new observational, experimental and genomic approaches to the study of SML are particularly welcome. This multidisciplinary session welcomes participants from all research fields interested in the SML and its impact on surrounding environments. The session aims to bring together insights and findings from field observations, laboratory experiments, and models. By exploring the interplay between physical, chemical, and microbiological processes at the ocean-atmosphere interface, we seek to further develop a holistic perspective and foster new collaborations across research disciplines.

Anthropogenic disturbance of the global nitrogen (N) cycle has more than doubled the amount of reactive N circulating in the terrestrial biosphere alone. Exchange of reactive/non-reactive nitrogen gases between land and atmosphere including reactive N deposition on ecosystems are strongly affecting Earth’s atmospheric composition, air quality, global warming, climate change, human health and biodiversity. This session seeks to improve our understanding of a) how intensification of reactive N use, land management and climate change affects the pools and fluxes of nitrogen in terrestrial and aquatic ecosystems, b) and how reactive N enrichment of land and water will affect the future carbon sink of natural ecosystems as well as atmospheric exchanges of reactive (NO, N2O, NH3, HONO, NO2 and non-reactive N (N2) gases with implications for global warming, climate change and air quality, and c) how fluxes, in particular N deposition, can be quantified with the necessary accuracy to be used in nature protection policies as well as emission regulation and mitigation strategies. We welcome contributions covering a wide range of experimental and modelling studies, which covers microbes-mediated and physico-chemical transformations and transport of nitrogen across the land-water-air continuum in natural ecosystems from local to regional and global scales. Furthermore, the interactions of nitrogen with other elemental cycles (e.g. phosphorus, carbon) and the impacts of these interactive feedbacks for soil health, biodiversity and water and air quality will be explored in this session. Latest developments in methodological innovations and observational and experimental approaches for unravelling the complexities of nitrogen transformations and transport will also be of interest. This session will be celebrating its 10th anniversary for nitrogen science and cycling at the EGU2025.

Aerosol particles are key components of the earth system; important in dictating radiative balance, human health, and other areas of key societal concern. Understanding their formation, evolution and impacts relies on developments from multiple disciplines covering both experimental laboratory work, field studies and numerical modelling. In this general session all topics of Aerosol Chemistry and Physics are covered. Contributions from aerosol laboratory, field, remote sensing and model studies are all highly encouraged.

Alongside general contributions, this year we also propose a focus on the increasing uptake and use of tools under the banner of Data Science and AI. Adoption of machine learning can be found across all areas of science, including atmospheric aerosol research. We see increasing use of a range of tools, from computational image tools for improved detection and classification through to development of hybrid numerical models. However we must also recognize the importance of the broader data science ecosystem, from evolving regulations, standards and increased emphasis on data discoverability and provenance. With this in mind we welcome submissions that full under a broad range of atmospheric aerosol applications. This could include, but are not limited to:
- Improved classification of aerosol types from spectral, time-series through to image datasets
- Identification of new processes as a result of ML adoption
- Highlighting new challenges in adopting ML in aerosol research
- Improved understanding of process and parameter sensitivity
- Development of Digital Twins
- Development of hybrid process-ML based aerosol models
- Increased resolution and/or computational efficiency of numerical methods
- New ‘Machine Learning’ ready data repositories
- Use of foundation models and generative AI in atmospheric aerosol research

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

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

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

Primary biological aerosol particles span a wide range of sizes from tens of nanometers to up to 100µm. Bioaerosols is a ‘catch all’ term to denote airborne microorganisms (airborne fungi, bacteria, pollen, virus and their constituents). Bioaerosols, or subsets of bioaerosols are sometimes known by other terms such as primary biological aerosol particles (PBAPs), aeroallergens or BioPM. While these particles make a small contribution to the total aerosol number they contribute significantly to the total mass, with biological aerosol accounting for 15-25% of the total aerosol mass burden. The detection and classification of bioaerosol remains a significant technical challenge, where real-time methods capable of high temporal resolution are often limited by their discriminative capabilities, and offline methods which provide detailed speciation suffer from poor time resolution and difficulties in producing atmospheric concentrations. As such, accurately quantifying bioaerosol and understanding their impacts is of importance to an increasingly diverse range of research communities as they pose scientific questions relating to their influence on climate via cloud-aerosol interactions; the effects of allergenic species on public health and air quality and how this may be impacted by changes introduced by net zero policy; the agricultural health security impacts of pathogenic species; and the efficacy of early warning capabilities for national security and defence.

The aim of this session is to bring together expertise from a wide range of disciplines broadly studying bioaerosols. We welcome presentations covering topics on real-time detection methods and machine learning data processing techniques, technique validation, laboratory studies, indoor and outdoor ambient observations, the application and development of models, forecasting and nowcasting, exposure assessment and associated health impacts.

Cloud feedbacks are the dominant uncertainty in assessing global and regional climate sensitivity. As such, an improved understanding of the key processes involved in cloud formation, development, and radiative effects will support better representations of these processes in climate models and reduce uncertainty in future climate predictions.
Ice nucleating particles (INPs) and secondary ice production play crucial roles in cloud processes and radiative feedback, influencing weather patterns and climate dynamics. This session explores the intricate interplay between INPs, secondary ice production mechanisms, and their impacts on cloud properties from both observational and modeling perspectives.
We will discuss cutting-edge findings on the sources, distribution, and variability of INPs in different atmospheric conditions. Insights from observational studies, remote sensing techniques, and laboratory experiments will be integrated with advanced modeling approaches to elucidate the complex microphysical and radiative feedback mechanisms.
We then discuss the secondary ice production mechanism and highlight their influence on cloud formation, evolution, and precipitation processes. The session aims to foster discussions on improving our understanding of secondary ice production processes, their representation in climate models, and their implications for regional and global climate variability and change.
Topics covered in this session are:
- Laboratory studies related to ice nucleating particles or secondary ice production
- Ice nucleation processes and characterizing INP in the field
- Modelling of secondary ice production
- Improving parameterizations associated with cloud formation in models – deep convective clouds, mixed-phase clouds, mesoscale convective systems
- Arctic Amplification and the effect of polar clouds on the global climate system


Solicited Speaker: Dr. Paul Zieger, University of Stockholm, Sweden.
Solicited Presentation: "On the abundance and sources of biological aerosol serving as ice nuclei in the high Arctic".

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

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

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

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

We are delighted to announce that in the 22nd edition of the dust session, Dr Patricia Castellanos (NASA) will provide a solicited talk about her work on airborne observations of dust.

In recent years, microplastics and nanoplastics have become recognised as ubiquitous atmospheric pollutants. However, many open questions remain regarding emissions, transport and deposition of microplastics and nanoplastics, along with atmospheric processes that determined their fate. In this session we welcome contributions from observational, laboratory and modelling studies that advance the field of airborne microplastics and nanoplastics research, including:
- Sampling and analysis of airborne micro- and nanoplastics
- Atmospheric microplastics and nanoplastics and their interactions with different environmental compartments (oceans, land and the cryosphere)
- Contributions of soils, roads and other terrestrial sources to the atmospheric micro- and nanoplastic burden
- Ocean-atmosphere exchange of microplastics and nanoplastics
- Interactions between micro- and nanoplastics and other sources of aerosol
- Interactions between microplastics, nanoplastics, radiation and clouds
- Airborne microplastics as vectors for chemical and pathogen transport
- Indoor, outdoor, urban, rural and remote microplastics and nanoplastics (measurements, observations, modelling)
- Toxicological and exposure studies related to airborne micro- and nanoplastics
- Degradation of macro-, micro- and nanoplastics in real and simulated atmospheric conditions
- Airborne sources and sinks of micro- and nanoplastics (measurements and modelling)

Rocket launches and re-entry of reusable and discarded objects adds anthropogenic trace gases and aerosols to almost all layers of the atmosphere. The space sector is the only anthropogenic emission source to the middle-to-upper atmospheres where pollutants can persist for decades, leaving a lasting legacy of atmospheric pollution. These pollutants are becoming increasingly ubiquitous due to the recent exponential growth of the space sector, yet there are no regulatory controls targeting these emissions. Quantification of the complex and unique effects on the atmosphere is mired by many uncertainties and data gaps, such as in the chemical composition of exhaust from novel propellants, the resultant evolution during plume afterburning, the locations and trajectories of launches and re-entry, the radiative and chemical kinetic properties of the pollutants, and the physics and chemistry of controlled or uncontrolled re-entry, ablation, and breakup. Meanwhile a lack of openly-available modelling tools is compounded by a scarcity of real-world experiments and observations, and both historical and future impact estimates are hindered by a lack of commercial space activity data or well-supported growth projections. This session invites submissions from all EGU disciplines by representatives in and beyond academia to share planned, current, or ongoing research that provides new knowledge in this area, explores new open-source modelling techniques, or exposes methodological gaps that need to be resolved to inform policies and for a truer determination of the influence of space activity on the atmosphere. We are also interested in innovative methods adopted by researchers focusing on volcanic emissions, geoengineering, and meteors that could be applied to the space sector.

Aeroallergens significantly impact various aspects of life, including health, the economy, and the environment. Currently, up to 30% of Europe’s population suffers from pollen allergies and asthma, with the number of allergy sufferers steadily increasing over the past few decades. This growing prevalence poses a substantial burden on public health systems and economies, with the annual costs related to allergies in Europe estimated to range between €50 and €150 billion.

In addition to their effects on human health, pollen and fungal spores negatively affect agriculture and forestry, contributing to reduced crop yields and forest health. Moreover, climate change exacerbates these issues, as rising temperatures and increased CO2 emissions disrupt plant life cycles. These changes lead to longer and more intense flowering seasons and shifts in the geographical distribution of certain species, which are both consequences and indicators of climate change.

Given the increasing concerns, there has been a paradigm shift in aeroallergen monitoring techniques. Traditional manual measurements are being replaced by automated in situ measurements, DNA sequencing-based methods, and remote sensing technologies. These advanced approaches do not only provide more accurate information about aeroallergens but also enhance model predictions and forecasts.

In this session, we invite contributions on the detection, analysis, and forecasting of aeroallergens as well as on studies dealing with their impact on climate, the environment and human health.

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 projects
CERTAINTY (Cloud-aERosol inTeractions & their impActs IN The earth sYstem) and CleanCloud (Clouds and climate transitioning to post-fossil aerosol regime) 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

Weather and climate events, such as heat waves, drought, and tropical cyclones, exert high influences on air quality. Meanwhile, two or more weather events may occur simultaneously to form compound extremes, which may exhibit intensified impacts on human health and ecosystem relative to the individual event. This session seeks contributions regarding the mechanistic understanding of the nexus between extreme weather events and air quality, and associated impacts on human health and ecosystem. Abstracts on observations, modeling and projections are all welcomed.

Volcanic aerosol clouds from major tropical eruptions cause periods of strong surface cooling in the historical climate record and are dominant influences within decadal surface temperature trends. Advancing our understanding of the influence of volcanoes on climate relies upon better knowledge of:

(i) the radiative forcings of past eruptions and the microphysical, chemical and dynamical processes which affect the evolution of stratospheric aerosol properties and

(ii) the response mechanisms governing post-eruption climate variability and their dependency on the climate state at the time of the eruption.

This can only be achieved by combining information from satellite and in-situ observations of recent eruptions, stratospheric aerosol and climate modelling activities, and reconstructions of past volcanic histories and post-eruption climate state from proxies.
In recent years the smoke from intense wildfires in North America and Australia has also been an important component of the stratospheric aerosol layer, the presence of organic aerosol and meteoric particles in background conditions now also firmly established.

This session seeks presentations from research aimed at better understanding the stratospheric aerosol layer, its volcanic perturbations and the associated impacts on climate through the post-industrial period (1750-present) and also those further back in the historical record.

Observational and model studies on the stratosphere and climate impacts from the 2022 eruption of Hunga Tonga are also especially welcomed.

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

The session aims to bring together research contributing to several current international co-ordinated activities: SPARC-SSiRC, CMIP7-VolMIP, CMIP7-PMIP, and PAGES-VICS.

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

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

Aircraft condensation trails (contrails) are currently estimated to contribute a similar effective radiative forcing as all CO2 yet emitted from the aviation sector. They also constitute the ultimate short-lived forcer, with lifetimes estimated in hours and local radiative forcings on the order of several watts per meter squared. This has made them the subject of a recent explosion in interest from the scientific, aviation, and regulatory communities, including ongoing debate regarding potential measurement and regulation of contrail formation alongside aircraft CO2 emissions.

Although there have been several recent in-situ measurement campaigns and significant recent advances in the detection of contrails using remote sensing data, understanding their overall climate effects - as well as the development of effective strategies to mitigate said impacts - requires accurate models of contrail formation and evolution. This is a substantial challenge, given that contrails form at the scale of an aircraft engine exhaust but can spread to be tens or hundreds of kilometers wide. Furthermore there remains relatively little observational data to directly constrain contrails due to the difficulty of directly sampling contrail ice and the high degree of temporal and spatial variability in cruise altitude conditions.

With these concerns in mind, this session aims to bring together the growing community of contrail modellers who are seeking to advance our ability to represent and understand the full lifetime of a contrail and its long term impacts. This includes those who are working on: high-fidelity modelling of contrail formation in the exhaust plume; LES or RANS models of the exhaust plume and contrail; 0-, 1-, 2-, or 3-D models of long-term contrail behaviour; models of regional- and global-scale contrail evolution and climate responses, including potential cloud feedbacks; and studies using new datasets to evaluate the performance of existing contrail models. Particular attention will be given to research using open-source models and data.

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

Solicited speaker: Prof. Bill Collins, UC Berkeley

A deeper understanding of the complex pathways associated with atmospheric aerosol sources, sinks, and transformation processes prevail as a major bottleneck in global climate research. Owing to their distinct atmospheric conditions, measurements from polar, marine, high-altitude and remote environments are crucial to reduce the uncertainties hovering around this issue. Despite their importance, aerosol characteristics in these regions are poorly understood due to limited observational data arising due to logistical challenges, harsh environments, and limited accessibility. This session addresses this research gap by focusing on recent expeditions and field campaigns to the Arctic, Antarctica, Himalayas, as well as marine, high-altitude and remote environments.
Topics of interest to the session include, but are not limited to:
• The physical and chemical composition of aerosols, their precursors, and roles in atmospheric processes, including new particle formation.
• The mechanisms driving aerosol generation, including the complex interactions between air-sea and air-snow interfaces, and chemical processes that lead to emissions of trace gases and volatile organic compounds.
• Light absorbing aerosols such as black carbon, brown carbon and mineral dust aerosols.
• Mixing state of atmospheric aerosols.
• Aerosol-cloud interactions and hygroscopicity of aerosols.
• Recent field campaign results that use ground, ship-based, and airborne measurements. This includes cutting-edge measurement techniques, such as UAVs, balloon-borne sensors, real-time automated ground-based systems, and newly established research infrastructures which enable the unique datasets from these regions.
• Use of field data in improving satellite retrievals and models simulating aerosol transport, atmospheric processes, and interactions with clouds and radiation.
• Laboratory experiments of aerosols.
By fostering collaboration and knowledge exchange, this session aims to advance the understanding of aerosol impacts in these regions, contributing to global climate change mitigation efforts.

Remote sensing of clouds and aerosols is of central importance for studying climate system processes and changes. New generations of active sensors (EarthCare), passive multi-angular polarimeters (PACE/SPEX and PACE/HARP-2, 3MI, CO2M MAP etc.) and single viewing instruments (hyperspectral Sentinel 5P/5/4, OLCI and SLSTR on Sentinel 3), will bring aerosol and cloud characterization on a new level. This will essentially boost our understanding of the physical/chemical processes in the atmosphere, specifically aerosol-cloud interactions. Nevertheless, till now, the number of challenges and unsolved problems remain in remote sensing algorithms and their applications.

This session is aimed at the discussion of current developments, challenges and opportunities in aerosol/cloud characterization and aerosol-cloud interaction studies, using active and passive remote sensing systems. We invite submissions of theoretical, methodological, and empirical studies to advance aerosol/cloud remote sensing and to understand better aerosol-cloud interactions and their effect on climate.

Significant uncertainties remain in our understanding of Carbon Dioxide (CO2) and Methane (CH4) fluxes across land, ocean, and atmosphere on both regional and global scales. Remotely sensed CO2 and CH4 observations hold great potential for enhancing our understanding of the natural carbon cycle and monitoring anthropogenic emissions. Recent advances in remote sensing technologies for CO2 and CH4, spanning space, aircraft, and ground-based platforms, have delivered unprecedented accuracy and coverage. Moreover, upcoming next-generation platforms like CO2M, MicroCarb, GOSAT-GW, and MethaneSAT promise to further enhance observational capabilities. When integrated with ground-based observation networks and modeling tools, these space-based observations can significantly improve our understanding of the carbon cycle at both local and global scales.

This session invites contributions on all aspects of remote sensing of CO2 and CH4, covering current missions (e.g., GOSAT/2, OCO-2/3, S5P, EMIT, Carbon Mapper, GHGSat, EMIT), upcoming and planned missions (e.g., CO2M, MicroCarb, Merlin, GOSAT-GW, MethaneSAT), as well as ground-based (e.g., TCCON, COCCON), aircraft, and other remote sensing instruments. We welcome advances in retrieval techniques, instrumental concepts, and validation activities, with a particular emphasis on interpreting observations related to natural fluxes or anthropogenic emissions.

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

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

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

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, GEMS, and TEMPO,
inter-comparisons of different remote sensing measurements dedicated to
tropospheric chemistry sounding and/or analyses with ground based
measurements and chemical transport models.

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

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

Source apportionment studies of air pollution aim to determine the sources of ambient particulate pollution, volatile organic compounds and other gases in the atmosphere. Receptor-oriented models (RMs) have become increasingly popular source apportionment methods among the research community and environmental protection agencies in the past two decades. RMs are designed to identify and quantify the measured mass of an atmospheric pollutant at a given site (the receptor site) to its potential emission sources by applying multivariate analysis to solve a mass balance equation. The results of RMs on atmospheric species are essential to policymakers for designing more effective air quality management strategies to reduce the health and environmental impacts of air pollution. This session aims to discuss case studies on the application of RMs as well as improvements and new methodologies on source apportionment of air pollution.

Despite the decline in the levels of many air pollutants due to the existing policies, air pollution remains associated with millions of premature deaths worldwide, including in Europe. A significant portion of the global urban population, including Europeans, has lived in areas with consistently unhealthy levels of particulate matter with an aerodynamic diameter smaller than 2.5 micrometers (PM2.5) and nitrogen dioxide.

Transportation plays a crucial role in the global distribution of food, materials, energy, and more. However, all transport sectors are substantial emitters of gaseous and particulate air pollutants. The influence of transport sectors on harmful ambient PM2.5 is not well understood, necessitating improved scientific understanding and evidence to justify policies and develop tools for policy implementation. This requires extensive emissions studies under real-world conditions, far beyond those used for the current emission standards. Additionally, emerging non-exhaust emissions (e.g. brake wear and tire microplastics) present new challenges.

The previous assumption that primary organic aerosol (POA) emissions are chemically inert has dramatically changed in the last decade. Evidence shows that both gases and particles continuously react in the atmosphere, creating complex chemical mixtures that are just beginning to be analyzed with new analytical tools. Furthermore, it is now clear that large fractions of volatile organic compounds (VOCs), inorganic secondary aerosol precursors, as well as secondary aerosol formation from those have been neglected in most past emission studies and consequently are not explicitly included in the current emission inventories.

This session invites interdisciplinary contributions (experimental and/or theoretical) ranging from characterization of emissions related to various types of transport, including emerging non-exhaust emissions (e.g. microplastics), to their atmospheric transformations, and potential impacts on climate and health. Contributions will span from fundamental studies to real-world evaluation and mitigation of transport emissions, aiming for a better description of air quality in different regions, particularly in high-impact zones.

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

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

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

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

The session focuses on the variability of the tropospheric and stratospheric chemical composition on the timescales from diurnal to decadal. It discusses the processes driving this variability and attribution of changes to specific drivers. Special emphasis is put on the value of high-quality long-term measurement data sets both from scientific and societal perspective, including science-policy applications, and their sustainability. Supporting model simulations on different scales that utilize observational data will also be discussed. Contributions related to emerging constituents, new data sources and approached to atmospheric composition measurements (e.g. low cost sensor, emerging measurement techniques), measurement campaign that addresses specific processes and long-term projections of the atmospheric chemical composition are also welcome in the session.
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 climate change, ozone depletion, ecosystems and health impacts, 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 weather and atmospheric composition (AC) are closely related. Still, Numerical Weather Prediction (NWP) from from the short-range to the seasonal range often only apply simplified presentations of aerosols, greenhouse gases and reactive gases, and NWP and AC forecasting is operated independently. However, recognizing the scientific and operational benefits of combining NWP and AC forecasting and data assimilation, integrated AC-NWP systems for global, regional, and local applications have been developed.

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

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

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

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

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

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

f) Data assimilation developments for AC and NWP,

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

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

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

This Session is organized in cooperation with the Copernicus Atmosphere Monitoring Service (CAMS) and the Global Air Quality Forecasting and Information Systems (GAFIS) initiative of the WMO Global Atmosphere Watch (GAW) Program.

Agricultural activities are one of the major contributors to trace gases in the atmosphere. Besides the contribution to methane (CH₄), nitrous oxide (N₂O), ammonia (NH₃), ground-level ozone (O₃), and various volatile organic compounds (VOCs) are triggered by agricultural activities. These trace gases play significant roles in biogeochemical cycles, affecting air quality and interplaying with climate change. Understanding the dynamics of the source and sink processes of these trace gases—from agricultural soils, crops, and the impact of diverse management practices—is essential for developing effective strategies or practices to mitigate their environmental impact.
This session, " Agricultural Trace Gas Dynamics and Air Quality: Innovative Approaches and Emerging Insights," aims to showcase the latest research and technological advancements in measuring and modeling trace gas exchanges and concentrations within agricultural ecosystems.
The session will welcome the following topics, but not limited to, (1) the impact of different agricultural management practices, such as tillage, mineral/organic fertilization, irrigation, crop rotation, and livestock management, on trace gas concentrations, emissions and depositions from a range of agroecosystems across the globe; (2) cutting-edge methodologies, such as ecosystem-scale monitoring, automated chamber systems, remote sensing technologies, and novel analytical tools for detecting VOCs and other trace gases; (3) the use of state-of-the-art modeling techniques, including artificial intelligence and machine learning, to extrapolate and predict gas dynamics patterns under various environmental and management scenarios; (4) challenges and opportunities associated with reducing the environmental footprint of agriculture.
We seek to bring together researchers, policymakers, and industry practitioners, especially the early career researchers, to join and contribute their fresh perspectives and ideas to this important discussion. Expected outcomes include fostering new collaborations, identifying research gaps on agricultural trace gas management and the challenges of climate change and air quality, and developing actionable recommendations for sustainable agricultural practices that may improve soil health, air quality, and global food security.

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.

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

This session invites results relating to radical measurements and modelling including:

1. The development of different techniques for radical detection and quantification, their precursors and intermediates species;

2. The adaption of instruments to different platforms (ground, mobile, shipborne, airborne, etc.);

3. Quality assurance (e.g. calibration procedures, inter-comparison of different techniques);

4. Model development (e.g. new chemical reactions/mechanisms, new model configuration, uncertainty analysis);

5. The implementation of radical measurements and modelling in the field and in chamber studies.

MERGED SESSION: This session focuses on two approaches for studying atmospheric processes:

I. Atmospheric Simulation Chambers and Laboratory Studies:
This session will concentrate on new scientific advances and technological progress concerning research in laboratory studies and with atmospheric simulation chambers like those in the European Infrastructure ACTRIS. This part comprises novel results in e.g. atmospheric chemical kinetics and modelling mechanisms, photophysical and photochemical processes, or aerosol formation and characterization. The focus of studies should be on new experimental developments, innovative enabling technologies and results of experiments that allow new knowledge for atmospheric science to be acquired.

II. Molecular Scale Observations
The substantial uncertainty surrounding regional and global anthropogenic climate change is largely due to our limited understanding of molecular-scale processes that govern atmospheric systems. These processes critically influence cloud properties and their climate impacts by modulating particle formation and growth. The atomistic properties of individual aerosol particles, their interactions with surrounding vapor-phase molecules, and the transport processes within the particle phase occur on temporal and spatial scales that are accessible through only a few specialized techniques. Among these, molecular simulations—such as molecular dynamics and Monte Carlo methods—and single-molecule experiments stand out for their uniquely high spatial and temporal resolution. Depending on the system, a variety of approaches are used—ranging from classical and reactive force fields to ab initio methods, with recent advances in machine learning further enhancing their capabilities. These approaches effectively complement traditional experimental and modeling techniques, and their recent adoption in characterizing molecular-scale properties is driving the emergence of a new interdisciplinary field at the intersection of molecular modeling and aerosol science. We invite contributions that apply single-particle or molecular-scale approaches to investigate aerosol properties—such as composition, structure, phase state, and shape—and processes critical to understanding the climate and health effects of aerosols. These processes may include new particle formation, cloud droplet and ice nucleation, and chemical reactions.