In this session we celebrate the 2026 awardees of the Atmospheric Sciences division through the Vilhelm Bjerknes Medal Lecture by Jonathan Williams and the Atmospheric Sciences Division Outstanding ECS Award Lecture by Eva Pfannerstill.

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.

8) Climate and Weather Interventions

Weather forecasting and its application is one of the most important subject in meteorology. This session will focus on R&D on weather forecasting techniques and applications, in particular those AI based techniques and application. Contributions related to nowcasting, meso-scale and convection permitting modelling, ensemble prediction techniques, and statistical post-processing are very welcome.

Topics may include:

- AI based Nowcasting methods and systems, use of observations and weather analysis
- Physics and AI driven Mesoscale and convection permitting modelling
- Development on AI for Ensemble prediction techniques and products
- AI for weather forecasting application
- AI for Seamless prediction and application
- Statistical and AI NWP Post-processing
- Use of machine learning, data mining and other advanced analytical techniques
- Presentation of results from relevant international research projects of EU, WMO, and EUMETNET etc.

Weather prediction and climate modelling extensively use numerical models of the Earth system. Both the atmosphere and ocean components of such models consist of a fluid dynamics solver (dynamical core) that solves a system of partial differential equations numerically. The dynamical core is coupled to physical parameterizations that represent processes that occur below the grid scale (physics). Enabled also by substantial improvements of the underlying numerical algorithms, these models can deliver accurate and efficient simulations.

Researchers are constantly working to further improve the accuracy, efficiency, and scalability of the dynamical core, the physics, and their coupling. The rapid development of computing systems towards massive use of graphics processing units and extreme parallelism requires adaptation of algorithms to further increase model efficiency via strong or weak parallel scaling. Recent years have also seen a rapid increase in hybrid approaches that combine physics-based modelling with data driven techniques, adopting techniques from scientific machine learning for Earth system modelling.

This session invites presentations on the development, testing, and application of novel numerical techniques for Earth system models in a broad sense. The scope includes modifications to the governing equations, horizontal and vertical discretizations, structure preserving methods, time stepping schemes (including parallel in time schemes), advection schemes, adaptive multi-scale models, physics-dynamics coupling, regional and global models, classical and stochastic physical parameterizations, as well as hybrid schemes combining numerical methods and machine learning.

This session invites contributions spanning all aspects of prediction and predictability on the subseasonal (2 weeks to 2 months) forecasting timescale, also known as subseasonal-to-seasonal (S2S) prediction. We welcome interdisciplinary research that covers predictions, processes, early warning capabilities and which supports applications and decision-making across sectors (including, but not limited to, the examples listed below). In light of recent advances in artificial intelligence (AI) and machine learning (ML) techniques for subseasonal prediction, contributions on AI/ML model developments, benchmarking frameworks and applications are very welcome. Of special interest are contributions related to the AI Weather Quest, an open international competition benchmarking AI-based subseasonal forecasts in real-time.

Physical drivers and processes
-Role of the atmosphere, ocean, land, and ice processes in extended-range/S2S predictability;
-Modes of variability (e.g., Madden Julian Oscillation (MJO), quasi-biennial oscillation (QBO), polar vortex strength, and others) impacting the extended-range/S2S predictability;
-Impact of global warming on early warning systems, changes in risks.

Prediction systems
-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;
-Use of AI/ML methods for S2S prediction, data-driven models, post-processing, and attribution, including innovative techniques for improving forecast accuracy.

Extreme events and early warnings
-Early warnings for single- and multi-hazard events;
-Sources of predictability for extreme events, including multi-hazards events, on the S2S timescale (including driver identification and teleconnections);
-Case studies of extreme or high-impact event prediction and impacts on early warnings;
-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.

Applications and societal relevance
-Sector-specific applications, impact studies on the S2S/extended range timescale;
-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.

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

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.

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

Clouds are ubiquitous and play an important role in modulating Earth's climate by modulating incoming and outgoing radiation. A challenge in understanding the impact of clouds arises from the multi-scale nature of cloud processes, which span from aerosol activation at the nanometer scale to the dynamics of cloud systems at the scale of hundreds of kilometers. Key microphysical processes, including droplet collision-coalescence, ice crystal formation, and their modulation by turbulence, occur at scales smaller than 100\;m, which poses a challenge to observe or simulate them. The uncertainty is further exacerbated by turbulent interactions with the environment through entrainment, mixing of air, and radiative changes within the cloud. Hence, we need to improve our understanding on the small-scale to increase our confidence in climate projections.

The superposition of small-scale processes calls for an integrated approach that combines laboratory experiments, field observations, and numerical modeling. Field observations characterize cloud processes within their natural, dynamic environment using a combination of remote sensing and in-situ measurements. Recent advances in observational platforms (e.g., uncrewed aerial systems), measurement techniques (e.g., multi-frequency cloud radar), and experimental designs have enhanced these capabilities. Controlled laboratory experiments allow for the isolation and systematic study of specific cloud processes under defined and repeatable conditions. High-resolution, process-oriented numerical modeling enables the study of fundamental interactions, can test hypotheses, and synthesizes datasets. These models need constraints and validation by data from both laboratory and field campaigns.

This session invites contributions that advance the understanding of small-scale cloud processes. A particular emphasis is placed on synergistic studies that combines laboratory experiments, field observations and/or numerical modeling .

Cold clouds (mixed-phase and ice) play an important role in the Earth’s radiation budget because of their high temporal and spatial coverage and their interaction with long wave and short wave radiation. Yet, the variability and complexity of their macro- and microphysical properties, the consequence of intricate ice particle nucleation and growth processes, make 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 (retrievals), which are useful to constrain cloud properties like extent, emissivity, or crystal size distributions, to clarify formation mechanisms, and to provide climatology.

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

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 and rapid runoff and flooding, weather forecasting, climate modelling, avalanche hazard forecasting, and the remote sensing of snow. The characterization of snow thus demands synergistic 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 as well as of rain-on-snow (ROS) events rapidly altering snow properties and changing snow microstructure. 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.

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).

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.

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.
- Machine-learning approaches for precipitation modelling, forecasting, and downscaling: Machine-learning and hybrid (physics-informed) methods for precipitation simulation, uncertainty quantification, bias correction, and spatio-temporal downscaling, including baseline comparisons, cross-climate transfer tests, and evaluations of explainability and robustness.
- 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.

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. We particularly welcome the first results from the 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.

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 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 (CAESAR, NAWDIC, (AC)3, ISLAS, etc.), long-term observations, reanalysis data, regional to global model simulations, or (isotopic) data assimilation;

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

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

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

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

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

Traditionally, hydrologists focus on the partitioning of precipitation water on the land surface into evaporation and runoff, while ignoring factors that influence precipitation. However, more than half of the evaporation globally returns as precipitation on land. Given this important feedback of the water cycle, changes in land-use and water-use, as well as climate variability and change, impact not only the partitioning of precipitation water but also the atmospheric input of water as precipitation, 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.
Applied studies in this session may adopt 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 data sources for atmospheric hydrology and implications for inter-comparison and meta-analysis. Examples of data sources and methodological approaches include observation networks, isotopic studies, conceptual models, Budyko-based hydroclimatological assessments, back-trajectories, reanalysis and fully coupled Earth system model simulations.

Extra-tropical cyclones and storms are key drivers of weather variability, extremes, and associated socio-economic impacts across densely populated regions of the globe. Understanding their observed and projected trends is crucial for improving climate diagnostics, risk assessments, and adaptation strategies in a warming climate. Most of our fundamental theories for the large-scale atmospheric circulation in the extra-tropics are based on “dry” atmospheric dynamics. Despite these recent efforts, large uncertainties in representing diabatic processes and their impact remain, leading to upscale error growth and enhanced ensemble spread, highlighting the continued need to further our understanding and to develop new and revise existing paradigms. This session therefore addresses both fundamental scientific challenges and urgent societal needs by linking physical processes, climate change signals, and potential impacts.

This session welcomes contributions covering mid-latitude storm systems, including but not limited to the following topics:

• Fundamental dynamics of cyclones - in all different stages of their life cycle - and their mesoscale features (fronts, jets, precipitation structures, dry intrusions)
• Role of diabatic processes for the dynamics, predictability, and future changes of extratropical weather system
• Representation of mid-latitude storms in AI-based weather and climate models
• Diagnostics of observed and projected trends in cyclone frequency, intensity, and storm tracks; including potential insights from contributions from measurement campaigns
• Predictability and forecasting on synoptic to sub-seasonal time scales
• Innovative methods, including AI/ML approaches, for cyclone detection, classification, or impact assessment
• Storm-related impacts, vulnerabilities, and risk-transfer mechanisms under a changing climate

By bringing together communities working on dynamics, diagnostics, impacts, field campaigns, and new methodologies, this session aims to provide a comprehensive platform for advancing our understanding of mid-latitude cyclones and their role in the past, present, and future climate system.

Solicited authors:
Suzanne L. Gray, Julian F. Quinting

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" creating nonlinear circulation features, such as atmospheric blocking.

Recent extreme weather and climate episodes, like heavy rainfall events leading to flash floods, recurrent and concurrent summer heatwaves or unforeseen winter cold spells, 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 and of atmospheric blocking 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.

Connect with colleagues across disciplines at the 4th Lagrangian session!

This session provides an open venue for scientists to share the latest advances in Lagrangian techniques, explore diverse applications, and build new connections.

We invite presentations on topics including, but not limited to:
- Planetary circulations and variability (fundamental processes shaping jets, gyres, waveguides, overturning circulations, transport barriers across atmosphere and ocean)
- Mesoscale eddies and coherent structures (eddy transport, wave-mean flow interactions, blocking)
- Turbulence and mixing (turbulent and convective entrainment, breaking internal waves, boundary layers)
- Numerical and computational advances (incl. data-driven techniques, GPU acceleration, graph-theoretical formulations, adaptive methods, data assimilation)
- Inverse modeling techniques (long-range transport of volcanic plumes, wildfire smoke, hazardous material, aerosols, plastics, micro-organisms, and their impacts on global composition, health, and climate)
- Field campaigns (drifters, floats, superpressure balloons, etc)

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.

Mountains cover approximately one-quarter of the total land surface on the planet, and a significant fraction of the world’s population lives within them, 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 showcases 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. 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 welcome are contributions that align with and address the interdisciplinary objectives of the Elevation-Dependent Climate Change (EDCC) working group of the Mountain Research Initiative, as well as the application and development of high-resolution (kilometer-scale) climate models over complex mountainous terrain, including advances in model design, challenges, and observational gaps needed for robust model evaluation and improvement.

TEAMx (www.teamx-programme.org) is an international research programme that aims at improving our qualitative and quantitative understanding of transport and exchange processes in the atmosphere over mountainous terrain and at evaluating how well these processes are represented in numerical weather and climate prediction models. One of its main scientific goals is to provide a unique observational dataset to study the exchange processes over a broad range of spatial and temporal scales. To this purpose, several measurement campaigns were conducted in the European Alps, including the one-year long TEAMx Observational Campaign (TOC) that took place between 2024 and 2025 targeting multiple processes contributing to the total exchange within the atmosphere, the HEFEX campaigns on Hintereisferner investigating glacier-atmosphere exchange processes, and additional smaller test campaigns in preparation for the TOC.

This session welcomes all contributions related to the TEAMx research programme, including observational studies resulting from one of the measurement campaigns as well as model and climatological studies.

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 have profound impacts on water, energy, and food security. Monsoons cause severe floods and droughts as well as undergoing variability on subseasonal, seasonal-to-decadal and palaeoclimate time scales. In addition to their profound local effects, monsoon variability also causes global-scale impacts via teleconnections, and the monsoons are linked together as part of the global monsoon via the divergent circulation, with aspects of coherent variability and interactions with planetary scale transports of heat and moisture.

Monsoons are complex phenomena involving coupled atmosphere-ocean-land interactions and remain notoriously difficult to forecast at NWP, subseasonal and seasonal scales, casting doubt also on our future climate projections. A better understanding of monsoon physics and dynamics and their response to forcing, 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 and compound weather events, NWP modelling, S2S and decadal forecasting, and the latest CMIP findings to help inform the IPCC AR7.

Atmospheric processes in both the tropics and midlatitudes are central to shaping weather, climate, and extreme events in the subtropics. The complexity of these processes and their interactions give rise to a unique hydroclimate characterized by strong spatial gradients, distinct seasonal cycles, and high sensitivity to variability and change. Subtropical regions are global hotspot regions of climate change, and yet, remain plagued by large uncertainty in climate model simulations. They are also home to a large share of the world’s population, including communities in the Global South that are disproportionately at risk from extreme events and climate change. Despite their societal and scientific importance, subtropical weather and climate processes remain comparatively understudied.

This session invites contributions that advance process understanding and prediction of weather and climate with a particular focus on the subtropics. We welcome studies based on observations, theory, numerical models, and machine learning. Topics of interest include, but are not limited to:
• Atmospheric processes shaping clouds, circulation patterns, dust and air pollution transport, and surface weather such as tropical–extratropical interactions, subtropical jet fluctuations, Rossby wave dynamics, transient eddies, monsoon circulations, and convergence zones.
• Weather, climate, and compound extremes – droughts, heatwaves, wildfires, heavy precipitation, flooding, dust storms, and windstorms – spanning their drivers, future changes, and impacts on society and ecosystems.
• The water cycle – rainfall, evapotranspiration, and moisture transport – modulated by weather systems such as cyclones, cutoff lows, cold air outbreaks, mesoscale convective systems, easterly waves, and atmospheric rivers.
• Coupled interactions between Earth system components, including land-atmosphere and ocean-atmosphere feedbacks, and the role of sea surface temperature patterns in shaping subtropical climate.
• Climate variability and remote linkages with ENSO, the Madden-Julian Oscillation (MJO), and the Hadley circulation.
• Observations and climate model simulations addressing past and future changes in regional circulation patterns and surface weather, and novel approaches for identifying model biases and for reducing uncertainties in projections.

Atmosphere-ice interactions are triggered by synoptic weather phenomena such as cold air outbreaks, polar lows, atmospheric rivers, Foehn winds, and heatwaves, and they impact snow, ice, and permafrost.

However, our understanding of these processes is still incomplete. Despite being a crucial milestone for reaching accurate projections of future climate change in Polar Regions, deciphering the interplay between the atmosphere, land ice and sea ice on different spatial and temporal scales, remains a major challenge.

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

We invite contributions on all observational and numerical modelling aspects of Arctic and Antarctic meteorology and climatology, that address atmospheric interactions with the cryosphere. This may include but is not limited to studies on past, present and future of:

- Atmospheric processes that influence sea-ice (snow on sea ice, sea ice melt, polynya formation and sea ice production and transport) and associated feedbacks,

- The variability of the polar large-scale atmospheric circulation (such as polar jets, the circumpolar trough and storm tracks) and impact on the cryosphere (sea ice and land ice),

- Atmosphere-ice interactions triggered by synoptic and meso-scale weather phenomena such as cold air outbreaks, katabatic winds, extratropical cyclones, polar cyclones, atmospheric rivers, Foehn winds, and heatwaves,

- Role of clouds in polar climate.

- Role of aerosols, such as black carbon, organic carbon, dust, volcanic ash, microplastics, pollen, sea salt, diatoms, bioaerosols, bacteria, in snow/ice melt and albedo changes.

- Teleconnections and climate indices and their role in land ice/sea ice variability.

Presentations that include new observational (ground and satellite-based) and modeling methodologies specific to polar regions are encouraged. Contributions related to results from recent field campaigns in the Arctic and in the Southern Ocean/Antarctica are also welcome.

In recent decades, dry-hot compound extremes, characterized by concurrent droughts and heatwaves, have significantly changed in their intensity, spatial modes, and temporal evolution. These emerging changes may reflect that the climatic boundary conditions causing dry-hot compound extremes could cross critical thresholds, with potential cascading effects that are fundamentally shifting the pattern of dry-hot compound extremes toward a new regime. This poses novel and often unanticipated extreme disasters, severely challenging the adaptability of local ecosystems and human health. This session aims to advance our understanding of dry-hot compound extremes by integrating observational analyses, climate modeling, and artificial intelligence frameworks. Key focuses include: 1) Novel theories and methodologies for heatwave understanding—elucidating mechanisms from the perspective of land-atmosphere-ocean coupling; 2) Drivers and mechanisms—elucidating dynamic (e.g., atmospheric circulation shifts) and thermodynamic (e.g., direct warming effect of greenhouse gases) processes changing compound events; 3) Long-term changes—quantifying historical trends, current intensification, and future trajectories under emission scenarios; 4) Climate effects—assessing impacts on vegetation, ecosystem carbon cycling, and its modulation on aerosol formation.

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.

Complementary middle-atmosphere sounding techniques—such as infrasound, lidar, radar, microwave spectrometry, and mesospheric airglow observations, further strengthened by satellite measurements—have become significantly more accessible over the past decade. It is expected that developing multi-instrument platforms will expand the community involved in operational infrasound monitoring for near-real-time observation of high-impact natural hazards—including volcanic eruptions, earthquakes, meteoroid entries, and bright fireballs—while creating new opportunities for atmospheric remote sensing research, such as improving gravity wave parameterizations.

In particular, global and regional infrasound station networks have proven highly effective in detecting and locating a wide range of natural and anthropogenic phenomena. Recent studies have shown that multi-technology analyses provide foundations for addressing geophysical inverse problems, enabling novel probing of both global-scale and small-scale structures in the middle atmosphere for enhanced weather prediction and climate modeling.
In addition to data-driven contributions, this session invites model-based papers dealing with the dynamics of the middle atmosphere across scales and altitudes, as well as its predictability. We welcome contributions on the characterization of atmospheric phenomena (gravity or planetary waves for example), using complementary observational methods across both local and global scales. Contributions addressing advances in wave propagation modeling, signal processing, and machine learning applications are also of great interest. Additional areas of focus include the development of derived data products and services for scientific and civilian use, as well as innovative instrumentation, including sensors deployed on mobile or elevated platforms such as balloons on Earth or other planets. Seismo-acoustic studies investigating the coupled Earth–ocean–atmosphere system, particularly focusing on ionospheric responses to processes originating from the ocean and solid Earth, are also encouraged.

Atmospheric rivers (ARs) are narrow and transient channels 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 at regional to global scales. 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
• ARs and the surface energy budget
• 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 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 global and regional climate projections under anthropogenic climate change, and for predicting the associated impacts on extreme weather and climate events. This session encourages theoretical, modelling and observational research on the large-scale atmospheric circulation, including (but not limited to) the following topics:
-Response of the large-scale atmospheric circulation to climate change, including shifts and changes in intensity of the jet stream, Hadley and Walker cells, intertropical convergence zone, and monsoons;
-Changes in storm track intensity and structure in response to climate change and/or internal variability;
-Representation of the large-scale atmospheric circulation in climate models: inter-model variability, model biases, and methodologies for reducing uncertainty in model projections;
-Novel metrics and analysis methods for studying the large-scale atmospheric circulation;
-Interactions between the different components of the large-scale circulation, including tropical-extratropical interactions and teleconnection patterns;
-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.

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. To be prepared for potential future extreme weather events, we 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) and if and how these dynamics are changing. 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.

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

Extreme weather and climate conditions, such as recent events unprecedented in the observational record, have extensive impact globally. Some of these events would have been nearly impossible without human-made climate change, and broke records by large margins. Furthermore, compounding hazards and cascading risks resulting from these high-impact extremes are becoming evident. Continued warming does not only increase the frequency and intensity of such 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 hazards and their associated 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 across all spatial and temporal scales, and covering compound, cascading, and connected extremes as well as worst-case scenarios, with the ultimate goal to provide actionable climate information to increase societal preparedness to such extreme high-impact events.

We invite work addressing high-impact extreme events via, but not limited to, model experiments and intercomparisons, diverse storyline approaches such as event-based or dynamical storylines, climate projections including large ensembles and unseen events, 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 societal impacts.

The session is sponsored and closely linked to the World Climate Research Programme lighthouse activitIES on 'Understanding High-Risk Events' and 'Explaining and Predicting Earth System Change'.

We invite contributions on all aspects of Meteorology and Climate for Renewable Energy (RE):
• Energy: wind, solar, hydro, tidal, wave, geothermal etc
• Spatial: microscale, mesoscale, synoptic and global
• Temporal: seconds, minutes, diurnal, seasonal, interannual, decadal and climatological
• Approach: measurement, modeling
The success of wind power has pushed turbines and research need into increasingly complex environments — mountainous terrain, forested areas, high in boundary layer and offshore. For solar power, new installation sites such as floating PV both rivers, water reservoirs for artificial snow, and “alpine PV farms” are gaining more attention. We need accurate measurements and short-term forecasts of cloud fields and aerosol effects. For weather-dependent renewables, the challenge of integrating shares into the power grid requires advances in understanding forecast uncertainty and spatio-temporal variability. Furthermore, meteorological conditions define how much power can be sent through the power grid and could help prevent curtailment or negative energy pricing.
Specifically, we invite contributions including but not limited to:
• Measurement techniques and analysis for e.g., wind, solar, hydro, and marine resources.
• Wind conditions (resource, extremes, turbulence) on all scales in complex environments (mountains, forests, coastal, offshore, urban).
• Wake effect models and measurements
• Forecast performance and uncertainty of RE at different time horizons
• Forecasts and detection of extreme and adverse weather events (wind ramps, droughts, heatwaves, storms, compound and consecutive)
• Detection and forecasting of dynamic line rating suitable conditions
• RE resource and atlas development (wind, solar, hydro, wave, thermal)
• Hydro-meteorological analyses of inflow variability, snowpack, precipitation extremes, and their implications for hydropower
• Tidal and wave resource assessment and predictability
• Impacts of renewable power plants or their large-scale integration on local, regional, and global scales
• Tools for strategic planning of RE in urban areas and smart energy systems.
• Climate Change Impact studies for renewables and weather-driven energy demand
• Interannual to decadal variability of renewable resources
• Typical Meteorological Years and probability of exceedance metrics
• AI and Machine Learning for weather and climate forecasting and applications to RE

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

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

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

Surface exchange fluxes of heat, momentum and mass above the global oceans and at the poles (snowpack, sea-ice, ocean and land) have significant impacts on atmospheric composition, biogeochemistry and climate at regional to global scales. Atmospheric boundary layer processes mediate these chemical and physical fluxes. This session is intended to provide an interdisciplinary forum to bring together researchers working in the areas of meteorology, atmospheric chemistry, air quality, biogeochemistry, stable isotope research, oceanography, and climate above the global oceans and in the polar regions.

The session focuses on new research in several areas which include: air-sea fluxes of climate-active trace gases (CO2, CH4, N2O) mediated by the atmospheric boundary layer above the oceans and in polar regions; regional emission and vertical mixing of aerosol, such as cloud-forming particles (CCN/INP) and their precursors (including dimethyl sulfide (DMS), marine organic compounds and halogenated species) and their impacts on atmospheric composition and climate; atmospheric deposition of nutrients (e.g., nitrogen, phosphorus, iron) and its impact on ocean biological systems; and biogeochemistry-climate feedback loops in the ocean-atmosphere system. We also welcome studies on how these surface fluxes may change in response to climate warming, as well as the local to large-scale influences on these exchanges. An adequate understanding and quantification of these processes is necessary to improve modeling and prediction of future changes above the oceans and in the polar regions, their teleconnections with mid-latitude weather and climate (including meridional transport of heat, moisture, chemical trace species, aerosols and isotopic tracers), and the coupling between local and large-scale dynamics.

The session has strong links to the Surface Ocean ̶ Lower Atmosphere Study (SOLAS) and the GESAMP Working Group 38 on atmospheric input of chemicals to the ocean. Submissions are encouraged from all areas covered by these programs, using a range of analysis approaches including field measurements, remote sensing, laboratory studies, and atmospheric and oceanic numerical models.

This year we particularly welcome studies on the impact of extreme events on air-sea gas exchange of climate-relevant compounds in marine systems. Here we invite contributions addressing physical drivers such as marine heatwaves, storms and tropical cyclones, circulation anomalies or sea ice changes; biogeochemical drivers such as hypoxic or anoxic conditions and acidification pulses; biological drivers such as harmful algal blooms; or compound events. Relevant studies may address impacts in all oceanic domains; e.g., open ocean, shelf waters and shallow (< 20 m depth) coastal ecosystems. The reporting on progress as well as critical knowledge gaps in polar regions will help define upcoming research programmes as part of Antarctica InSync and the International Polar Year 2032-33.

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, properties and impacts relies on developments from multiple disciplines covering both experimental laboratory work, field studies and numerical modelling. This session covers all aspects of Aerosol Chemistry and Physics. Contributions from aerosol laboratory, field, remote sensing and model studies are all highly encouraged.

Beyond the general topics, we recognize the rapid development of digital technologies has begun to transform and even lead new directions in aerosol research. Cloud computing, digital twins, and artificial intelligence are providing unprecedented capabilities for this field. These approaches span multiple scales, from single particles to global systems, and from process-level understanding to impact attribution. This session will spotlight the growing role of digital technologies in aerosol chemistry and physics. We invite contributions that explore the application and highlight key discoveries enabled by digital technologies. At the same time, we also emphasize the importance of balancing innovation with rigor: conclusions and processes must be carefully validated, uncertainties explicitly assessed, and data-driven methods integrated with theory, process models, and experimental observations to ensure reliability and reproducibility. Through this lens, this session aims to discuss both the opportunities and responsibilities of integrating digital technologies into aerosol research.

We welcome submissions that fall under a broad range of atmospheric aerosol applications. This could include work on the role and impact of:
- Advance fundamental understanding of aerosol chemistry and physics
- Development of hybrid process-machine learning based aerosol models
- Increased resolution and/or computational efficiency of numerical methods
- Applications of AI-enabled (e.g., GenAI, foundation models) and new-generation tools in aerosol research
- AI-enabled interpretation/prediction of aerosol variability and consequences, from characterizing properties to forecasting extreme events and quantifying impacts
- Development of new physical and digital platforms/technologies for aerosol research
- Open science practices: benchmark datasets, reproducible workflows, model sharing, and evaluation standards

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 efforts enhance our understanding of the origin and (trans)formation processes of 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 observations, chamber and modelling 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.

Biological particles 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.

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; and the efficacy of early warning capabilities for national security and defense. In addition to their effects on human health and climate, pollen and fungal spores negatively affect agriculture and forestry, contributing to reduced crop yields and forest health. Climate change exacerbates these issues, as rising temperatures and increased CO2 emissions alter plant life cycles and fungal emissions.

Given these increasing concerns, there has been a paradigm shift in bioaerosol monitoring techniques. Traditional manual measurements are being progressively replaced by automated in situ measurements, advanced omics techniques and remote sensing technologies. These advanced approaches do not only provide more accurate information about bioaerosols but also enhance model predictions and forecasts. However, 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 rich taxonomic information suffer from poor time resolution and difficulties in producing atmospheric concentrations.

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, validation, laboratory studies, indoor and outdoor ambient observations, the application and development of models, forecasting and nowcasting, exposure assessment and associated health impacts.

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. 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 and theoretical concepts of all aspects of the dust cycle (emission, transport, deposition, size distribution, particle characteristics),
(2) numerical simulations of dust on global, regional, and local scales,
(3) meteorological conditions for dust storms,
(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 biosphere, cryosphere, and hydrosphere,
(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., and early warning systems

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 23rd edition of the dust session, Dr Claudia Di Biagio (LISA) and Dr. Diego Villanueva (ETHZ) will provide solicited talks about their work on dust radiative properties and dust-driven droplet freezing.

Cloud feedbacks remain the dominant source of uncertainty in estimates of global and regional climate sensitivity. Advancing our understanding of the key processes governing cloud formation, evolution, and radiative effects is therefore essential for improving their representation in climate models and reducing uncertainties in future climate projections.
Cloud condensation nuclei (CCN), ice-nucleating particles (INPs), and secondary ice production (SIP) are central to cloud microphysical processes and radiative feedbacks, with far-reaching influences on weather and climate dynamics. This session focuses on the interactions between aerosols, CCN, INPs, and SIP, and their impacts on cloud properties, based on both laboratory and field studies.
Particular attention will be given to the Southern Ocean (SO), one of the cloudiest regions on Earth. Its pristine aerosol environment offers a natural laboratory for disentangling fundamental aerosol- cloud -radiation interactions in the relative absence of anthropogenic pollution, thereby providing critical insights into cloud microphysical processes.
We invite contributions that address pressing open questions on the coupling between gas-phase chemistry, aerosol nucleation and growth, cloud development, precipitation, and radiative impacts, with an emphasis on the Southern Hemisphere. Special focus will also be placed on advancing our understanding of SIP mechanisms, their influence on cloud evolution, and their representation in weather and climate models.
Topics of interest include:
• Laboratory studies on INPs and secondary ice production
• Aerosol, CCN, and INP sources and characteristics from field measurements (e.g., in-situ flight campaigns)
• Modeling of secondary ice production processes
• Advances in parameterizations of cloud formation and development in models (e.g., deep convective clouds, mixed-phase clouds, mesoscale convective systems)

Solicited Speaker: Prof. Dr. Mira Pöhlker, Leibniz Institute for Tropospheric Research (TROPOS), Germany.
Solicited Presentation: " The interplay of Clouds, Aerosols and Radiation above the Southern Ocean".

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
- New constraints on aerosol, clouds or precipitation from EarthCARE
- Observational constraints on aerosol-cloud interactions
- Use of observational simulators to constrain aerosols, clouds and their radiative effects in models
- Explorations of cloud seeding or artificial cloud brightening techniques
- 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

The polar regions are experiencing rapid and profound environmental changes, with the Arctic warming at nearly four times the global average. Aerosol-cloud interactions remain one of the largest sources of uncertainty in climate models, particularly in these fragile and rapidly evolving environments. Mixed-phase clouds, biogeochemical processes in the ocean and sea ice, and atmospheric dynamics all contribute to complex feedbacks that modulate Earth's radiative balance, influence weather systems, and drive climate change.

This session, inspired by the goals of initiatives such as QuiESCENT (Quantifying the Indirect Effect: from Sources to Climate Effects of Natural and Transported aerosol in the Arctic), CATCH (Cryosphere and ATmospheric CHemistry), CIce2Clouds (Coupling of ocean-ice-atmosphere processes: from sea-Ice biogeochemistry to aerosols and Clouds), and BEPSII (Biogeochemical exchanges at Sea Ice Interfaces), aims to foster interdisciplinary collaboration by bringing together researchers studying aerosols, clouds, ocean–ice biogeochemistry, and their coupled interactions in both the Arctic and Antarctic. We seek to bridge disciplinary gaps—spanning aerosols and clouds, physics and chemistry, observations and modeling, and ocean–ice–atmosphere processes—to advance our understanding of polar climate systems.

We invite contributions that address the following key topics:
- Aerosol-cloud interactions: Their influence on cloud microphysics, radiative properties, and precipitation patterns in polar environments, including the contrasting effects of anthropogenic pollution and natural aerosols.
- Biogeochemical cycling: Marine and terrestrial sources of aerosols, including sea salt, mineral dust, biological particles, black carbon, and organic aerosols, and their feedbacks with atmospheric components.
- Boundary layer dynamics: The role of atmospheric and oceanic boundary layer processes in shaping aerosol and cloud properties, as well as their impact on boundary layer mixing and local pollution processing.
- Observational and modeling advances: Innovations in field campaigns, remote sensing, laboratory experiments, and modeling frameworks to improve the representation of polar aerosol–cloud–ocean–ice systems in climate models.
- Climate feedbacks and projections: Implications of polar aerosol–cloud interactions for climate model performance and global climate predictions, with a focus on reducing uncertainties in projections.

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

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

Along with the rapid economic development and accelerated urbanization process, many areas in the world are suffering from high levels of ozone and fine particle pollution. These air pollutants can affect weather and climate system through absorbing or scattering radiation. For example, ozone is a kind of greenhouse gases, while aerosols can not only directly affect solar radiation but serve as cloud ice nuclei or ice nuclei to modify microphysical processes of clouds and precipitation. On the other side, weather and climate are also closely linked to formation of air pollution. Monsoon climate, stagnant weather conditions and large-scale circulation patterns all play important roles in air pollution. Understanding how weather and climate interact with air pollution at present and in the future can help us in the field of air pollution prevention and mitigation of global warming.

This session aims to address the current challenges, methodological approaches and wider relevance of observing and modelling meteorology-atmospheric environment interactions around the world. We welcome contributions including, but not limited to, integrating multi-source data (such as, on-situ monitoring, remote sensing, etc.) with controlled experiments to identify the key processes, modelling of the interactions between climate change and air pollution as well as the future projections, assessment the impact of extreme weather on air pollution and future trends, and illustrating the development of cities and the effects of urban climate on regional air quality. Research that reveals the impact of air pollution on the environment, ecology and human health is also welcome.

he Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) satellite, launched in May 2024, is an ESA-JAXA mission, designed to improve our understanding of clouds, aerosols and their role in modifying radiant energy fluxes. To achieve its objectives, EarthCARE employs a suite of coincident active and passive sensors to provide an unprecedented view of the three-dimensional structure of clouds, precipitation and aerosols along with collocated observations of solar and terrestrial radiation.
 
EarthCARE, provides co-registered observations from a suite of four unique instruments located on a common platform: (1) ATmospheric LIDar (ATLID), (2) Cloud Profiling Radar (CPR), (3) Multi- Spectral Imager (MSI) and (4) BroadBand Radiometer (BBR). EarthCARE global observations include vertical profiles of natural and anthropogenic aerosols, the vertical contribution of ice and liquid water content, the cloud mesoscale distribution, precipitation microphysics, estimates of particle size, convective vertical air motions, as well as atmospheric radiative heating and cooling profiles. In addition to providing novel measurements for a better understanding of processes shaping Earth’s weather and climate, EarthCARE continues the heritage measurements of CloudSat, CALIPSO, Aeolus and CERES.
 
This session invites contributions on EarthCARE science themes related to the exploitation of mission data. These include instrument characterization, new active and passive retrieval techniques; cloud and precipitation microphysics, process studies related to the effects of clouds, aerosol, and aersol-cloud interactions on Earth’s radiant energy budget; as well as synthesis with other methodological approaches including ground-based, air- or ship-borne field campaigns and modelling studies. A special focus will be on the synergy with modeling activities exploiting the next generation of km-scale climate models, as in ECOMIP and within the global km-scale hackathon, and observational studies in combination with Organized Convection and EarthCARE Studies over
the Tropical Atlantic (ORCESTRA).

Remote sensing of clouds and aerosols is of central importance when studying processes and changes in the climate system. The new spaceborne generation of active sensors (e.g. EarthCare), passive multi-angular polarimeters (e.g. PACE/SPEX, PACE/HARP-2, 3MI, CO2M, MAP) together with single-viewing instruments (e.g. hyperspectral Sentinel 5P/5/4, OLCI and SLSTR on Sentinel 3) will take the characterisation of aerosols and clouds to a new level. This will significantly improve our understanding of physical and chemical processes in the atmosphere, particularly aerosol-cloud interactions, and climate and radiation studies. Nevertheless, there are still many challenges and unsolved problems in remote sensing algorithms and their applications.

The aim of this session is to discuss current developments, challenges and opportunities in the characterisation of aerosols and clouds, in the study of aerosol-cloud interactions and their long-term effects, using ground-based, airborne and spaceborne active and passive remote sensing systems. We invite submissions of theoretical, methodological and empirical studies to advance the field of aerosol/cloud remote sensing, and to improve our understanding of aerosol-cloud interactions and their effect on the climate.

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 aerosols.

We welcome presentations based on studies analysing data from current and future
satellite missions, including the geostationary GEMS and TEMPO platforms and the
recent S4, S5, IRS, IASI-NG and 3MI instruments. Topics also include the
inter-comparisons of different remote sensing measurements dedicated to
tropospheric chemistry sounding and/or analyses with ground-based
measurements and chemical transport models.

This session is organized for the second time at EGU General Assemblies and reflects the recent emerging trends of atmospheric monitoring: (i) realising multi-instrument synergy retrieval and (ii) bridging three branches of atmospheric research (modelling, in situ measurements, and remote sensing).

This session encourages discussions that explore the synergies of complimentary observations, such as synergies of passive imagery with active vertical profiling of the atmosphere, synergies of observations in different spectral ranges and at different time and/or spatial scales, and synergies of satellite observations with sub-orbital observations and chemical transport model simulations. Synergy is important because the quality of measurements cannot be radically improved once the instruments have been deployed, but algorithms can continuously evolve and notably improve results with data fusion and optimization of the joint sensitivity of multi-instrument datasets. The the session especially welcomes the ides and demonstrations of synergy methods and Interdisciplinary applications using novel observations from the , EPS-SG, MTG, PACE, Copernicus Sentinels, EarthCARE and other recent and forthcoming advanced satellite missions (e.g., CO2M) as well as field campaigns.

The session also invites presentations that demonstrate the benefits of collaboration amongst the three core fields of atmospheric aerosol studies outlined in the Models, In situ, and Remote sensing of Aerosols (MIRA) international working group, which was formed to facilitate collaborations and improve discussions amongst these fields of study and across regional boundaries. More information can be found at https://science.larc.nasa.gov/mira-wg/.

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 and energy flows 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.

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, Merlin, and TANGO 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/GW, OCO-2/3, S5P/S5, IASI-NG, Carbon Mapper, GHGSat), upcoming and planned missions (e.g., CO2M, MicroCarb, Merlin, TANGO), 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.

Methane is an important greenhouse gas that has contributed to ∼25% of the increase in radiative forcing experienced to date. Despite methane’s short atmospheric lifetime (~10 years), the global average methane mole fraction has increased three times faster than carbon dioxide since 1750. Rapid and severe reductions in methane emissions are required to lower peak warming, reduce the likelihood of overshooting warming limits and reduce reliance on net negative carbon dioxide emissions. In order to track mitigation efforts and ensure emission quantification required in legislation can be met, we must be able to accurately attribute and quantify emissions and are actively doing so through activities such as the UNEP International Methane Emissions Observatory (IMEO).

This session will highlight measurement studies at all scales and from ground-based to satellites, that focus on quantification and source attribution of methane emissions from human activities. We especially encourage submissions from both IMEO and non-IMEO funded work that focus on the following topics: (1) new technologies / methods to provide accurate and repeatable emissions measurements, (2) demonstration of affordable and reliable quantification methods for mitigation tracking, (3) attribution of emissions to specific sources and, (4) methods for upscaling measurements into inventories and creating policy relevant datasets.

Methane is a potent short-lived climate forcer, and rapid mitigation measures are crucial for meeting climate targets and limiting currently expected temperature overshoots. This session will explore these methane mitigation measures, spanning emissions reduction approaches, novel point-source oxidation technologies, and potential atmospheric methane removal approaches.
We invite contributions covering:
- Assessment of methane emission reduction approaches
- Novel and emerging methane mitigation approaches, including emissions destruction and atmospheric removal
- Measurement and verification of mitigation effectiveness
- The role of methane mitigation in future climate scenarios

Atmospheric radicals (such as OH, HO2, RO2, NO3, halogen atoms and halogen oxides) play a central role in the oxidation of trace gases, contributing to the formation of secondary pollutants and influencing Earth’s climate. A thorough understanding of radical sources, including precursor species like HCHO, HONO, organo-halogens, and ClNO2, as well as their chemical fate, such as the conversion of primary pollutants and methane (CH4) oxidation, is essential for addressing regional air quality issues and climate change. 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 environments as different as the polar troposphere during the springtime ozone depletion events, the boundary layer over salt lakes, and volcanic plumes. Although measuring and modeling radicals is critically important, it remains highly challenging due to their low concentrations, high reactivity, and the complex reaction networks they participate in.

This session welcomes contributions related to the measurement and modeling of radicals, including:
1. Development of novel techniques for detecting radicals, their precursors, and intermediate species;
2. 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 species.
3. Adaptation of instruments for various platforms (e.g., ground-based, mobile, shipborne, airborne);
4. Quality assurance and control, such as calibration procedures and intercomparison of different methods;
5. Model development, including new chemical mechanisms, model configurations, and uncertainty analysis;
6. Applications of radical measurements and modeling in field campaigns and satellite-measurements including volcanic plumes as well as chamber studies.

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

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

The composition of the upper troposphere and the lower stratosphere (UTLS) plays a key role in the climate system. Our understanding of the interactions between dynamics, chemistry, and climate in this region is rapidly advancing thanks to both observational and modeling 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 that introduce recent observations (both in situ and remote sensing) and models of various complexity ranging from comprehensive chemistry climate models to idealized and conceptual models.
This year, field campaigns of special focus include recent projects that explore atmospheric transport, composition, and chemical processes in the spring Arctic UTLS, like ASCCI 2025 and COLD SABRE 2023.

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

The 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.

Molecular hydrogen (H₂) is gaining global attention as a key component of the transition to sustainable energy systems, with the potential to significantly reduce greenhouse gas emissions and air pollutants. However, the biogeochemical cycle of H₂ and its impacts on atmospheric chemistry and climate present critical knowledge gaps. While hydrogen itself is not a greenhouse gas, its chemical oxidation can influence methane, ozone, and stratospheric water vapor, with potential effects on the Earth’s radiative balance.

This session aims at advancing our understanding of the hydrogen budget and the implications of increased hydrogen use. Topics of interest include:
- Quantifying hydrogen emissions from direct sources, including leakages, venting, and incomplete combustion, as well as oxidation by volatile organic compounds.
- Investigating the removal of hydrogen by soil bacteria and by reaction with OH in the atmosphere.
- Assessing the indirect climate effects of hydrogen emissions on methane, ozone, and stratospheric water vapor.
- Utilizing observations and modeling to refine estimates of hydrogen sources and sinks across various spatial and temporal scales.
- Exploring scenarios of future hydrogen economies, including their potential to reduce fossil fuel emissions and the associated environmental and climatic co-benefits.

We welcome studies that employ experimental, observational, and theoretical approaches to hydrogen biogeochemistry and atmospheric processes, contributing to a more comprehensive understanding of H₂ in the context of the global energy transition.

Urban air pollution comprises a complex mixture of pollutants, including particulates, trace gases, and volatile organic compounds, primarily from anthropogenic activities. The composition has been changing due to shifts from petroleum and diesel vehicles to those powered by compressed natural gas (CNG) and liquefied petroleum gas (LPG), which produce 95% less NOx than diesel and 65% less than petrol. Many nations are now focusing on electric vehicles (EVs), altering emission profiles and air pollutant chemistry through atmospheric transformation, photochemical reactions, and aging processes. These atmospheric pollutants create various health impacts, with studies linking air pollution to increased respiratory conditions.

This session at the European Geosciences Union (EGU) invites submissions on observational and modeling studies of emerging air pollution emissions and chemistry, including their climate and health impacts.

This session aims to bring together the scientific community within air pollution modelling, focusing on modelling the atmospheric transport and transformation of air pollutants and precursors on global, regional and local scales.

Atmospheric composition and air quality are at the core of global environmental change, with profound implications for public health, ecosystems, and policy. Fine particulate matter, ozone, and reactive trace gases increasingly interact with wildfires, heatwaves, urbanization, and climate variability, creating complex exposure patterns and disproportionate risks for vulnerable groups.
New frontiers in satellite monitoring—from Low Earth Orbit to geostationary platforms—combined with chemical transport models and artificial intelligence, now allow unprecedented accuracy in characterizing pollution sources, dynamics, and health outcomes. At the same time, integrative frameworks linking atmospheric science, epidemiology, and socio-economic analysis are essential for informing effective adaptation and mitigation strategies.
This interdisciplinary session invites studies that advance understanding of atmospheric composition, air quality, and health through innovative observations, modeling, and AI applications. We especially encourage contributions that explore climate–air quality–health interactions, quantify health and economic burdens, develop early-warning systems, and provide policy-relevant insights. The session aims to foster cross-disciplinary collaboration to support evidence-based decision-making for cleaner air and healthier societies.

The transport sector, which includes road traffic, shipping, and aviation, is a significant contributor to global warming and has detrimental effects on air quality. The combustion of fossil fuels results in the emission of gases and particles that alter the chemical composition of the atmosphere. These gases can act as direct greenhouse gases, such as CO2, or undergo complex reactions, forming secondary species. The emitted particles interact with radiation and affect clouds. Emissions from aviation can also lead to the formation of contrails, which affect natural cloud formation processes. While some of these non-CO2 effects contribute to global warming others to cooling.
Due to the significant increase in demand, the contribution of aviation to climate change is expected to grow. Additionally, emissions from road traffic and shipping may also increase depending on changes in mobility and technological advancements. Therefore, it is crucial to develop and implement measures and methods to reduce the anthropogenic climate footprint, including the share of different transport modes. Possible methods to reduce the environmental impact of transport include alternative fuels, such as electricity or hydrogen, and technological advancements, such as after-exhaust treatment systems. Besides these rather technical measures, also operational measures are possible, such as optimized routes.
However, the assessment of the effects of such measures and methods with numerical atmospheric models relies heavily on state-of-the-art emission inventories. It is crucial to provide information on the uncertainties in the emission data to ensure a dependable assessment of air quality and climate effects. This information also contributes to the uncertainties in the representation of physical, chemical, and dynamic processes in atmospheric models.
The objective of this session is to bring together the community involved in the development of transport emissions inventories with the community involved in the use of these inventories. On one hand, the aim is to establish a shared understanding of the different requirements and uncertainties related to emission inventories. On the other hand, particular attention will be given to the latest research on the non-CO2 and air quality effects of transport emissions. Contributions can range from measurement campaigns to modelling results and implementing strategies for reducing the environmental impact of transport.

Over the last twenty years, a significant portion of the global urban population, including Europeans, has lived in areas with consistently unhealthy levels of particulate matter (PM10, PM2.5, ultrafine particles). Despite the reduction of many air pollutants due to earlier policies, air pollution remains associated with millions of premature deaths worldwide, including in Europe.
Transportation plays a crucial role in the global distribution of food, materials, energy, and more. However, all transport sectors are substantial emitters of air pollutants. The influence of transport sectors on harmful ambient PM is not well understood, necessitating increased scientific understanding and evidence to justify policies and develop tools for policy implementation. Addressing key questions requires extensive emissions studies under real-world conditions, far beyond current emission standard protocols. Additionally, emerging sources like non-exhaust emissions and microplastics present new challenges.
The previously simple view of chemically inert primary organic aerosol (POA) has dramatically changed in the last decade. It is now clear that large fractions of volatile organic compounds (VOCs) have been neglected in most past emission studies and are not explicitly included in current emission inventories. 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.

This session invites interdisciplinary contributions, both experimental and theoretical, ranging from real-world emissions related to various transport sectors, including new sources like non-exhaust emissions and microplastics, to their chemical transformations in the air and potential impacts on climate and health. Contributions are expected from fundamental studies to the evaluation and mitigation of these pollution sources, aiming for a better description of air quality in different regions, particularly in high-impact zones.

A constellation of geostationary satellite ultraviolet-visible (UV-VIS) spectrometers with air quality related trace gas and aerosol observational capabilities is in orbit forming a Geo-Ring in the Northern Hemisphere. These include Geostationary Monitoring Spectrometer (GEMS) launched in February 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 launched in July 2025 by European Space Agency over Europe. A very successful demonstration of GEMS and TEMPO trace gas and aerosol products in air quality monitoring and forecasting is paving the way for the newly launched Sentinel-4 UVN instrument. 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 Low Earth Orbiting satellite sensors 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 involving international collaboration to minimize data gaps in the Global South.

Cities are hotspots for emissions of air pollutants and greenhouse gases from traffic, industry, household energy use, and other human activities. Many urban emissions originate indoors (e.g. cooking, heating, solvent use) before entering the outdoor atmosphere, while outdoor pollution infiltrates indoor environments where people spend most of their time. Indoor–outdoor exchange processes, together with urban meteorology and city geometry, influence pollutant concentrations, chemical transformations, human exposure, and urban carbon budgets. Air pollution impacts may be cumulative or episodic, and can be exacerbated during heat waves, while greenhouse gases are often co-emitted with air pollutants, making cities both major drivers of climate change and focal points of climate-related health impacts.

This session brings together researchers working on urban air quality, greenhouse gases, and the indoor–outdoor air pollution interface. We invite contributions on urban air pollution, heat stress, urban carbon budgets, indoor and outdoor emission sources, indoor–outdoor exchange processes, and air pollution impacts on health. Topics include sensor networks, personal monitoring, airborne observations, high-resolution modelling and downscaling, source apportionment and isotopic attribution, ambient and indoor atmospheric chemical processes, biogenic and anthropogenic precursors to secondary pollution formation, community and personal exposure quantification, allergens, and air pollution and climate-related health effects.