Weather prediction has improved tremendously over the last decades. Ultimately, however, there are limits in predictability due to the multi-scale, non-linear nature of atmospheric dynamics.
To further improve our mechanistic understanding of atmospheric dynamics and to further improve numerical weather forecasting it is increasingly important to better understand the physical and dynamical processes connecting atmospheric motions across temporal and spatial scales. This includes, for example, the identification of the limits of predictability of different weather systems. For longer time scales, identifying and understanding sources of predictability and variability is of crucial importance. This session will therefore discuss the current understanding of physical and dynamical processes determining predictability and variability on different scales.

Contributions are invited that attempt to improve our understanding of atmospheric dynamics or that link process-based, dynamical understanding and predictability aspects. Atmospheric phenomena on all spatial and temporal scales are of interest. Particularly welcome are contributions that focus on high-impact weather, the sub-seasonal to seasonal (S2S) timescale, and related extremes. This may include, but is not limited to, the influence of remote factors (e.g., the stratosphere, the Artic, or the tropics) on the midlatitudes, predictability in the tropics and polar regions, stationary and recurrent systems (e.g. associated with heat waves, cyclone clustering, heavy precipitation), or processes driving seasonal or interannual variability.

Atmospheric Boundary-Layer processes on a variety of temporal and spatial scales strongly influence weather, air quality and climate. These processes include atmospheric turbulence, atmosphere-soil-vegetation interactions, gravity waves, boundary layer interactions with dry and moist convection, mesoscale flows, et cetera. These processes should be well-understood to enable accurate and skilled weather and air quality forecasting, as well as reliable climate model and scenario studies to serve society with high quality weather and climate information.

This session welcomes contributions on research into the understanding of boundary-layer processes and turbulence from either a conceptual, or modelling or observational perspective, their role and interactions and finally their implementation in atmospheric modelling.
Papers dealing with the following topics are invited:
• Theoretical and experimental studies of the turbulence-closure problem with emphasis on very stable stratification and convection, accounting for interactions between the mean flow, turbulence, internal waves and large-scale self-organized structures
• Boundary-layer clouds and marine, cloud-topped boundary layers: physics and parameterization within NWP and climate models
• Orographic effects: form drag, wave drag and flow blocking, gravity waves
• Challenges on the surface exchange processes, flux aggregation in atmospheric boundary layers over heterogeneous terrain
• Representation of boundary layers in atmospheric models
• Organization of deep convection across differing atmospheric scales
• Large-eddy simulation and direct numerical simulation of turbulent flows.

This session will welcome all technical and scientific contributions devoted to increasing our understanding of atmospheric phenomena that might represent a hazard for people, property and environment. Studies devoted to enhance physical understanding of severe weather phenomena (for example deep convection or intense straight lines winds) are of particular interest even if the severe weather phenomena are not linked directly to a specific hazard. Embracing the proposal given by the organizers for this year, particularly welcome will be the contributions dealing (directly or indirectly) with the Artic area or underlining aspects connected to artic drivers of atmospheric hazards.
Moreover, in line with the suggestions given by EMS 2019 meeting committee, we would encourage contributors to underline intercultural aspects of their methods and findings, and to point their attention not only to the physical and meteorological characteristics of atmospheric hazards, but also to their relevance in a changing climate including possible impacts on human activities and the environment.
Contributions dealing with studies of specific episodes (case studies) will be welcome, provided they further increase physical understanding and are representative at least for the area where these events took place.
Particularly welcome will be contributions incorporating both numerical and conceptual modelling to improve our understanding of severe weather phenomena.
In general we will encourage the exchange of expertise and experiences related to the various topics connected to hazardous atmospheric phenomena and severe weather events. For this reason an interdisciplinary approach will be particularly welcome.
Potential topics for this session include i.a.:
• Flash-floods and heavy rain events;
• Hail;
• Freezing rain, icing and intense snow falls;
• Cold/heat events, even those occurring at small time scales;
• Fog;
• Tornadoes, waterspouts, derechos and downbursts;
• Severe wind storms;
• Intense Mediterranean cyclones;
• Tropical like cyclones;
• Lightning;
• Polar lows, their evolution and impacts;
• Severe katabatic or foehn winds;
• Gap and orographic flows;
• Breaking of gravity waves, as well as severe turbulence;
The above-listed topics are of course not exclusive and the session’s Conveners eagerly anticipate papers on new ideas and approaches and novel understanding covering all aspects of atmospheric hazards and severe weather events.

Forecasting wind gusts may become the next major challenge in numerical weather prediction. With increasing computer power, operational NWP systems just entered the convective scale, allowing the model physics to simulate convective processes more explicitly. While this is very beneficial for precipitation forecasting, wind gusts are still a sub-grid scale phenomena relying on crude parametrizations. Furthermore, wind gusts cause large socio-economic damages every year. Wind gust predictions are getting higher relevance and load, e.g. for transport, aviation, urban development or public weather warnings. Yet forecast verification exhibits exceptionally low skill for wind gust predictions compared to other meteorological variables, which might also be impacted by a very sparse observational network. The spatial variability of wind gusts is probably as large as that of precipitation, but the observational network is much less dense and no equivalent to the spatial coverage of radar derived precipitation exists.

This session welcomes contributions which lead to a better understanding of the physical processes that determine wind gusts, and novel ideas/methods to improve wind gust forecasting and warnings in the future. More specifically, contributions on the following topics are welcome:

- Observations: The development of novel measurement tools for wind gusts (e.g. WindLIDARS) and suggestions for an optimized observational network in the future. Descriptions of the spatio-temporal variations of gusts.

- Explicit modelling: Small-scale model simulations (e.g. LES simulations) are a prerequisite to explicitly resolve the processes leading to wind gusts. Beside a better understanding of the physical processes they can be utilized to improve empirical approaches to approximate wind gusts more accurately.

- Wind gust forecasting and warnings: Methods to obtain guidance for wind gusts forecasts and warnings from operational weather forecasts, e.g. using historical observations by statistical postprocessing or forecast assimilation techniques. Prediction uncertainty of wind gusts.

- Climate monitoring: Long-term data sets for wind gusts as well as techniques for spatial wind gust analysis which are necessary for climate change adaptation and mitigation strategies

- Evaluation: The high-resolution model simulations on the one side and a sparse observational network on the other side require novel ideas in the verification of wind gusts simulations and warnings.

Measurements are essential to provide information on the actual state of the atmosphere for nowcasting purposes, for climate monitoring, for assimilation into numerical weather prediction (NWP) systems and to improve our understanding of atmospheric processes and their role in the climate system. In particular, there is a strong need for complex observations suitable to develop, improve and validate parameterizations used in NWP and climate models and to provide ground-truth against which to compare atmospheric parameters derived from satellite data. With a new generation of high-resolution forecast models (1-3 km) used for the prediction of high-impact weather, dense observational networks focusing on measurements in the lower few kilometers of the atmosphere are required.
This session is intended to give a forum to discuss recent developments and achievements in local to regional measurement concepts and technology. There will be a special emphasis on measurements which seek to improve our understanding of complex atmospheric processes – especially those characterizing interactions in the climate system – through obtaining comprehensive data sets. The focus is on measurements of atmospheric dynamics and thermodynamics, energy and water cycle components, and on the interaction of the atmosphere with the underlying surface. With respect to the special conference focus on the Arctic, contributions on measurements from that region are specifically invited.
The session will also include consideration of novel measurement approaches and networks under development for future operational use, e.g., within the frame of the Eumetnet observations program, and the performance of new measurement techniques. Manufacturers of hydro-meteorological instruments and system solutions are thus explicitly invited to present news on sensor development, sensor performance and system integration. Reports on metrological aspects of meteorological measurements are equally welcome.
Techniques may cover in-situ and remote sensing measurements from various platforms. Special attention will be given to the creation of a new generation of reliable unmanned instrument networks across Europe that provide calibrated and controlled data on the boundary layer structure in near-real time. Contributions are also invited that make use of advanced data sets for satellite data validation.

This session provides a platform for contributions on high-resolution precipitation measurements, analyses, and applications in real-time as well as climate studies. Monitoring and statistical analyses of precipitation at small spatial and temporal scales are challenging. Therefore, special focus is placed on documenting the benefit of highly spatially and temporally resolved observations of different measurement platforms, e.g. satellites, radar networks, or opportunistic sensing, e.g. retrieving rainfall from microwave links. Papers on monitoring and analyzing extreme precipitation events including extreme value statistics, multi-scale analysis, and event-based data analyses are especially welcome, comprising definitions and applications of indices to characterize extreme precipitation events, e.g. in public communication. Contributions on long-term observations of precipitation and correlations to meteorological and non-meteorological data with respect to climate change studies are cordially invited. In addition, contributions on the development and improvement of gridded reference data sets based on in-situ and remote sensing precipitation measurements (e.g., GPCC, OPERA) are welcome.
High-resolution measurements and analyses of precipitation are crucial, especially in urban areas with high vulnerabilities, in order to describe the hydrological response and improve water risk management. Thus, this session also addresses contributions on the application of high-resolution precipitation data in hydrological impact and design studies.
Summarizing, one or more of the following topics shall be addressed:
• Precipitation measurement techniques
• High-resolution precipitation observations from different platforms (e.g., gauges, disdrometers, radars, satellites, microwave links) and their combination
• Precipitation reference data sets (e.g., GPCC, OPERA)
• Statistical analysis of extreme precipitation (events)
• Multi-scale analysis, including sub-kilometer scale statistical precipitation description and downscaling methods
• Definition and application of indices to characterize extreme precipitation events
• Climate change studies on extreme precipitation (events)
• Urban hydrology and hydrological impact as well as design studies
• New concepts of adaptation to climate change with respect to extreme precipitation in urban areas

This session invites contributions to discuss the present meteorological conditions in the Polar Regions (Arctic and Antarctic) and changes of these induced by climatic drivers.
Since 1980, near-surface climate warming in the Arctic has proceeded at approximately twice the global rate. Simultaneously with the warming, the Arctic has experienced notable changes such as decrease in sea ice extent and thickness and glacier retreat. These changes have been accompanied by changes in precipitation and in the large‐scale atmospheric circulation patterns.
The Polar atmosphere has very specific features such as shallow boundary layers, stratified conditions with low mixing and extreme insolation characteristics during large part of the year. These flow and turbulence patterns are important for exchange of heat, GHG and cloud condensation nuclei between the surface and the atmosphere, as well as for dispersion and mixing into higher elevation.
Changes in surface temperature and sea ice and glacier extent affect the atmospheric flow, turbulence and stratification, as well as snow properties, which in turn affects radiation processes and balance. In order to estimate future implications of climate change in the Polar Regions, it is important to understand the present meteorology as well as its development due to surface and temperature changes. This has to be achieved through combining measurements and modelling of local to regional scale meteorology. More specifically but not exclusively the session will address:
• Past and present Polar meteorological conditions
• Processes contributing to Polar amplification of climate warming
• Extremely shallow and stratified boundary-layers,
• Physics and occurrence of Arctic clouds, precipitation and haze
• Observations in Polar regions: challenges, experiences, networks and demand
• GHG concentrations development and GHG exchange with the cryosphere (e.g. permafrost thawing)
• Polar climate change trends and their local and remote impacts on different time scales
• Meso- and micro scale modelling for Polar predictions
• Long-range transport routes and emissions in Polar Regions
• Parameterization of specific processes for modelling the Polar atmosphere.
• Contribution to and support from international programmes: WMO Year of Polar Prediction, Arctic Monitoring and Assessment Programme, Sustaining Arctic Observing Networks, MOSAiC drifting station, International Arctic Systems for Observing the Atmosphere, Pan-Eurasian Experiment, etc.

The session will cover a wide range of atmospheric and oceanographic phenomena occurring in coastal areas, from synoptic and mesoscale patterns down to local scale processes, both for research purposes and applications, including operational oceanography and related services (e.g., coastal resource management, wind-waves and circulation monitoring and predictions for the sake of maritime safety and navigation, marine environmental protection, coastal erosion).

Observational studies will be considered, including in-situ measurements, ground-based and space-borne remote sensing techniques (scatterometers, synthetic aperture radar, ...), focusing in particular on recent mission data (e.g., SENTINEL), operational campaigns (e.g., HyMeX), and European project results (e.g., CEASELESS).

Modeling studies, based on stand-alone atmospheric, waves and ocean circulation models, will be of interest for the session. However, the main focus will be on the new area of numerical coupled modeling, which combines the dynamics of ocean, atmosphere and waves in a fully two-way exchange context. Coupled model results will be analyzed on the climate scale, validated against observations, but also applied to specific case studies in short-to-medium range simulations. Within this framework, specific attention will be allocated to high-impact weather and related marine events affecting coastal areas, such as intense cyclones, severe wind storms and storm surges, heavy rain events, flash floods, and supercells, analyzed both from a meteorological, marine and climate change perspective.

Activities of interest for stakeholders, related to renewable energy spatial planning both onshore and offshore, coastal management, urbanization planning for smart coastal cities, are also very welcome.

This session is devoted to basic and applied research on atmospheric processes, phenomena and impacts linking the chemical and physical states of the atmosphere. Particular interest lies in the observations and modelling of the transport, dispersion, transformation and deposition of atmospheric compounds (including air pollutants, pollen, GHGs, radionuclides and other substances naturally or accidentally released) and how they interact with the local and global climate and weather.

Within this scope, the session draws from diverse elements of atmospheric science research related to weather, atmospheric composition and climate, and includes theoretical, numerical modelling and experimental studies on scales extending from local to global, including the urban areas. Contributions on the development of observations and modelling techniques as well as on mitigation strategies varying from nature-based solutions to emission reductions also fit the scope of the session.

Targeted towards both disciplinary and interdisciplinary audiences, this session invites oral and poster contributions on topics including, but not limited to, the following:
• Feedback processes between atmospheric compounds, meteorology, and climate
• Characterization of the effect of urban planning choices and other interventions on the emissions, transport, dispersion and concentrations of atmospheric compounds
• Observations and modelling of urban meteorology including street canyon circulation, heat and mass fluxes within and over cities
• The impact of boundary layer processes on the transport and dispersion of atmospheric compounds
• Novel air pollution and atmospheric composition monitoring networks and platforms
• Air quality and transport model development using meteorological and chemical observations
• Air quality forecasting/assesment (incl. online modelling integrating chemical weather with NWP modelling) and chemical data assimilation.

The session also serves as a dissemination forum for relevant projects, including the Copernicus Atmosphere Monitoring Service (CAMS), COST Actions, WMO Global Atmosphere Watch (GAW) SAG-GURME & SAG-APP, FAIRMODE, as well as national- and European-scale consortium projects and research infrastructures.

Solar "shortwave" irradiance is the main source of energy to the surface and the atmosphere. Outgoing thermal "longwave" irradiance and reflected shortwave irradiance is the only energy sink from the atmosphere. Both shortwave and longwave irradiances interact with the surface, clouds and aerosols in complex manners that are not yet comprehensively modelled in weather and climate models. Here, we will address the current state-of-the-art of these interactions, as they are represented in contemporary models. The increasing need for accurate radiation outputs for the growing renewable energy sector will also be addressed. Attention will be paid to the validation of modelled radiation output by using ground-based and satellite measurements of irradiances.

This session is expected to focus on the above points and to gather presentations and posters on the following topics:

• Handling of radiative transfer in clear and cloudy atmospheric boundary layers including three-dimensional radiative transfer aspects.
• Surface-radiation interactions including both general radiative properties of the surface and interactions with complex topographies and canopies.
• Evaluation of radiation and cloud output from NWP models and use of shortwave radiation measurements for cloud verification.
• General aspects of radiation and microphysics parametrizations and their interactions in NWP models
• Obtaining the inherent optical properties of cloud, precipitation and aerosol particles for the use of NWP models
• Time, space and spectral resolution of the radiation parametrizations required by the models from mesoscale to global circulation.

The cryosphere represents one of the Earth system compartments showing strong signs of dramatic changes due to climate forcing.
If global warming is actually the main common driver causing such changes, the rates, impacts and processes acting in the mountain and Polar regions can differ markedly.
Estimating the response of the global cryosphere to climate change as well as the response of the components of the climate system to changes in the cryosphere relies on understanding of climate-cryosphere interactions and processes in different regions and along different spatial and temporal scales.

Polar regions:
Sea ice and ice sheets in both polar regions are sensitive to atmospheric forcing. Changes in these cryosphere components influence the climate through changes in atmospheric and ocean circulation, sea level, albedo, vegetation and several related feedbacks.
In the Arctic, sea ice concentration and volume have recently experienced a sharp declining trend, and the Greenland Ice Sheet has similarly been losing mass at an increasing pace. Atmospheric forcing has played a crucial role in driving these trends and triggering positive feedbacks within the Arctic cryosphere-ocean-atmosphere system. These changes to the cryosphere may further feed back into large-scale climate variability through atmospheric and oceanic pathways.
At the other pole, sea and land ice in the Antarctic have heretofore experienced changes that strongly depend on the geographic location (e.g., east vs. west) and, overall, are less dramatic when compared to the changes observed in the Arctic cryosphere. Atmospheric influences on sea ice retreat and ice sheet/shelf surface melt are projected to become more prominent with continued climate warming.

Mountain regions:
The seasonal snow cover, mountain glaciers, permafrost and permanent ice deposits in caves are the main parts of the mountains cryosphere.
They affect the hydrology of a vast range of river systems in the world and are vital for the water availability particularly in arid high mountain regions.
The water volume stored in mountain glaciers is small compared to the water storage in Polar Regions, but increasing rates of glacier mass loss result in a significant contribution to recent sea level rise.
The observed permafrost degradation in mountain regions has severe implications on rock stability and increases the risk of natural hazards.
Permanent ice deposits in caves are probably the lesser known as well as the smallest part of the earth’s cryosphere, but it has been shown recently that they can store important palaeoenvironmental information.
Investigating the micro-climate over snow and ice surfaces and its linkage to large-scale weather conditions and model climate is fundamental for tackling the mass and energy balance of the mountain cryosphere.

Session:
Understanding the spatial and temporal variability of snow accumulation, storage and transport of ice and ice ablation in mountains and Polar Regions, and the interaction of the snow surface with the atmosphere within the boundary layer are crucial for interpreting proxy records from various archives such as ice cores.
This session invites contributions addressing all aspects of cold regions meteorology and the cryosphere interacting with the past, present and future climate system from both modelling and observations.
We encourage submissions from multiple approaches, i.e. past records, meteorological and geophysical observations, numerical modelling and downscaling methods aiming to advance the current knowledge of the feedbacks between the cryosphere and the climate system.
Presentations of interdisciplinary studies as well as detailed process surveys are highly welcome.

The Sun is the main energy source for the Earth's atmosphere. Important manifestations of such external forcing from space to the atmosphere are the variations in different solar parameters such as the solar irradiance (including solar UV) and solar particle fluxes, which can induce changes in the atmosphere both at local and global scales, and can influence over a large range of altitudes. Some of these changes have the potential to affect the troposphere through atmospheric coupling processes, particularly through the stratosphere-troposphere connection, and thus have the potential to influence weather and climate.
The field of space weather has seen a rapid increase in research activity in recent years, and associated large scientific advances. It is clear that the weather and climate community can benefit from this via better representation of space weather effects and their associated impacts on the Earth’s atmosphere.

The aim of this session is to provide a framework for reviewing the state-of-the-art on these issues and to identify possible interrelationships between Earth and the Sun and space weather by assessing the level of coupling in the relevant physical systems and processes.

Contributions from the following topics (but not exclusively) are invited:
• Solar irradiance and energetic particle impacts on the atmosphere
• Upper atmospheric dynamical variability and coupling between atmospheric layers
• Solar variations and stratosphere-troposphere coupling
• Solar influence on climate variability
• Solar irradiance (spectral and total irradiance) variations

Meteorology and hydrology act in tandem across the interface of the earth's surface, and as our understanding and predictive capabilities grow this interface is becoming increasingly important. For the good of society, the need to meld together the two disciplines is now stronger than ever. Indeed many national meteorological services around the world have been evolving, formally or informally, into national hydro-meteorological services. The aim of this new session is to provide a large and all-embracing hydro-meteorological forum where experts from both disciplines can join forces, to combine and exploit expertise, and to accelerate the integration process. We invite contributions across a wide-range of spatial scales (from 10s of metres up to global), and a wide-range of time scales (from ~1 hour up to seasonal and climate change), including, but not limited to, the following topics:
- land-atmosphere interaction and hydrological processes, including feedback mechanisms;
- understanding the meteorological processes driving hydrological extremes;
- tools, techniques, and expertise in forecasting hydro-meteorological extremes (e.g. river flooding, flash floods, droughts, etc.);
- fully integrated numerical earth system modelling;
- quantification/propagation of uncertainties in hydro-meteorological models;
- quantification of (past/future) hydrological trends in observations and climate models;
- hydro-meteorological prediction that includes the associated impacts;
- related cryospheric processes;
- environmental variable monitoring by remote sensing.

The European continent is in the lucky situation of hosting three Regional Hydroclimate Projects (RHPs) sponsored by the Global Energy and Water Exchanges Project (GEWEX) of the World Climate Research Programme (WCRP). These projects, though at various stage of their implementation, have the same objectives of providing a multi-disciplinary understanding of the water cycle under a changing climate and evolving human water usages. These RHPs cover three relatively different climates of Europe with their specific water challenges:
• HyMex: The Mediterranean region with extreme rainfall events and long droughts.
• BalticEarth: The Baltic region with its evolving cold conditions and biogeochemical linkages.
• PannEx: A transition climate in which humans have shaped the water usage during the last centuries.
The budgets between the various processes of the water balance (precipitation distribution and intensity, evaporation characteristics or contribution of surface and ground transports) are very different within each region and thus impacts of climate change will also differ. Two of these regions furthermore include the coupling to a closed sea. Human water usages have over the centuries adapted to the physical characteristics of the water cycle within each regional climate and are thus very different in all three regions.

In order to help prepare our societies to a different climate and ensure adequate water resources, we need to advance our process understanding and enhance our forecasting capabilities at all scales from days to centuries. Thanks to these RHPs we can bring together the critical mass of scientists of various disciplines to illuminate the different aspects of the water cycle and our water resources in each region. Focusing on certain regions also allows developing specific solutions for each of the regions and communicate more directly our knowledge to decision makers and the public at large.

This session invites oral and poster presentations dealing with the main scientific questions identified in these European RHPs. Several of these questions are common to other part of Europe and the world. Thus, this session will focus on the specific scientific, observational, forecasting, impact, application, collaboration and socio-economic issues:

• Water balance at the basin scale;
• Forecasting extreme rainfall events and their evolution in a warmer climate;
• Forecasting of Basin floods and flash floods: water for societal security under changing climate conditions;
• Understanding drought formation and improving early warning systems;
• Impact of irrigation on the water cycle;
• Agro-climatological and biological systems: Agriculture response to climate changes and weather extremes;
• Local climate interactions with energy fluxes: agronomical process modelling and micrometeorology,;
• Urban issues: urban metabolism, energy flows and interactions with surrounding areas;
• Regional climate modelling: Extreme weather and climate events as a risk to sustainable development;
• Regional Earth System processes which couple physical, biological and chemical cycles of the atmosphere, land and ocean.
• Impact and vulnerability assessments of climate changes and extreme weather events on different socio-economic sectors;
• Outreach, exploitation and education.

The conveners will also organise a short panel discussion within the session to examine which coordinated actions could be undertaken between the three European RHPs.

The timing of many phenological events of plants and animals is driven by temperature and other climatic parameters. Based on phenological observations valuable climate change indicators can be developed. On the other hand plant development itself has an impact on local and regional climatic parameters in temperate zones. Therefore, it should be considered in meteorological and climatological models.
Our ability to monitor plant phenology remotely, from satellites and cameras, for example, has greatly increased in recent years but we must also rely on in situ observations to track subtle differences between species in both the timing and duration of key phenophases which may contribute to the potential for carbon storage in mixed forest communities. Sources of useful phenology data and duration of the time-series are crucial to determine future responses of ecosystems to climate change.
The main focus of this session will be to determine the effectiveness of phenological data to analyse potential changes in land-atmosphere interactions in response to climate change. We invite presentations related to the following topics:
•Impact of extreme weather events on phenology-
•Use of phenology in agrometeorological impact models and in decision making
•Observing and recording phenology from in situ methods to remote sensing (satellites, phenocams, citizen science in phenology networks etc.)
•Use of future climate projections in phenology modelling
•Relationship between phenology and carbon and water fluxes across different ecosystems

The subject of the session will be the chemistry and the physics of short lived climate forcers (SLCF; black carbon, methane and ozone) in the Arctic atmosphere. The chemistry and physics of these species have been intensely studied at lower latitudes but in the Arctic their dynamics are still connected with large knowledge gaps and uncertainty due to the special Arctic conditions. Polar night represent one extreme condition with 24 hour darkness during polar winter leading to a very stratified troposphere and no photochemistry. Thereafter it is followed by another extreme situation with 24 hour-sunlight during polar summer. During this period special surface processes occur, where those related to halogen chemistry are most notable.
In the present session scientist are invited to submit their newest knowledge on SLCFs in the Arctic atmosphere.

Society will feel the impacts of climate change mainly through extreme weather and climate events, such as heat waves and droughts, heavy rainfall and associated flooding, and extreme winds. Determining from the observational record whether there have been significant changes in the frequency, amplitude and persistence of extreme events poses considerable challenges. Changes in the distributional tails of climate variables may not necessarily be coherent with the changes in their mean values. Also, attributing any such changes to natural or anthropogenic drivers is a challenge.

The aim of this session will be studies that bridge the spatial scales and reach the timescales of extreme events that impact all our lives. Papers are solicited on advancing the understanding of causes of observed changes in mean climate, in its variability and in the frequency and intensity of extreme events. In particular, papers are invited on trends in the regional climate of Europe, not just the mean, but variability and extremes, often for the latter measured through well-chosen indices.

Covariability between remote regions – often named teleconnections – are at the basis of our current knowledge of a large part of Earth’s climate variations and represent an important source of weather and climate predictability. Tropospheric and stratospheric pathways have been suggested to play a role in connecting internally-generated and radiatively-forced anomalies at mid-latitudes, as well as in settling tropical-extratropical and polar-nonpolar interactions. However, the underlying processes behind these linkages are still not properly understood, misled by different metrics and diagnostics, and/or generally poorly simulated by global climate models (GCMs). A continuous assessment of these atmospheric teleconnections is thus necessary, since advances in process understanding could translate into improving climate models and predictions.

This session aims at gathering studies on both empirical and modelling approaches, dealing with a dynamical characterization of mid-latitude atmospheric teleconnections. It invites contributions using observational datasets; coupled and uncoupled (atmosphere-only) GCM simulations; pre-industrial, present, and future climate conditions; idealised sensitivity experiments; or theoretical models.

Keynote talk:

Tido Semmler - Arctic influence on mid-latitude weather and climate: recent progress and future prospects

Synoptic climatology examines all aspects of relationships between large-scale atmospheric circulation on one side, and surface climate and environmental variables on the other. The session addresses all topics of synoptic climatology; nevertheless, we would like to concentrate on the following areas: statistical (empirical) downscaling, circulation and weather classifications, teleconnections and circulation regimes, and climatology of cyclones and other pressure formations, including effects of the circulation features on surface climate conditions. We also encourage submissions on recent climate variability and change studied by tools of synoptic climatology or otherwise related to synoptic-climatological concepts.

We invite contributions on theoretical developments of classification methods as well as on their use in various tasks of atmospheric sciences, such as climate zonation, identification and analysis of circulation and weather types, and synoptic catalogues. Climatological, meteorological, and environmental applications of circulation classifications are particularly welcome.

The session will also include presentations on statistical (empirical) downscaling as a tool for evaluation and reconstruction of historical climate, gap filling in time series, analysis of extremes and non-climatic variables. Also intercomparisons among downscaling methods and their validation belong to this session.

Contributions on teleconnections (modes of low-frequency variability) and circulation regimes are expected to cover particularly their impacts on surface weather, climate, and environment.

The contributions on climatology of cyclones and other pressure formations will include analyses of cyclone tracks, life time and intensity of cyclones, as well as analyses of anticyclones and blockings. We also invite studies on impacts of the pressure formations on the environment and society, their relationships with large scale circulation patterns, as well as analyses of their recent trends and behavior in possible future climates.

The exceptional amplitude and rate of warming recorded at global, hemispherical and regional scales within contemporary instrumental records should be placed in the context of longer-term multi-centennial and millennial climate variability in order to both assess its uniqueness and better understand the mechanisms that contribute to the background of natural climate variability. Systematic meteorological measurements only span over a relatively short time interval. Thus, documentary evidence and natural climate proxies are used for the reconstruction and understanding of longer term past climate variability.

This session welcomes presentations related to various topics related to this frame:
• early instrumental meteorological measurements, their history and use for the long-term series
• documentary evidence and its features (advantages, disadvantages limits)
• natural climate proxies and its features (advantages, disadvantages, limits)
• methodological improvements and analysis of climate reconstruction approaches both from documentary evidence and natural climatic proxies
• results of climate reconstructions over different regions based on various climatic sources
• hydrological and meteorological extremes (e.g. floods, hurricanes, windstorms, tornadoes, hailstorms, frosts) and their human impacts in relation to climate variability beyond the instrumental period.
• climate modelling of the last 2K and comparison of model outputs with reconstructed/observed climatological data
• past impacts of climate variability on natural processes and human society
• past and recent perception of the climate and its variability
• history of meteorology and meteorological and climatological knowledge
• discussion of natural and anthropogenic forcings as well as recent warming at global, regional and local scales in a long-term context.

Climate models have become a widespread tool to simulate the behavior of the climate system over longer time periods (e.g. multi-decadal to centennial). They are also increasingly employed to obtain climate predictions on timescales of seasons to decades. And as computational power has increased the ability to run these models at so-called convection permitting scales (<4km grid spacing) has lead to an explosion of activity that targets explicitly resolving multi-scalar aspects of the climate system and opens new lines of inquiry. Climate modeling contributes to the understanding of the complex interaction processes in the earth system and provides scenarios for future climate conditions. The results of climate modeling form the basis for recommendations and decisions on how to prepare for and adapt to climate change and forms the backbone of downstream development of many climate services. This session will be devoted to different aspects of climate modeling, including:
• advances and challenges in convection-permitting atmospheric modeling,
• development and refinement of global and regional climate models,
• numerical aspects of climate models,
• ensemble climate modeling,
• representation of physical earth system processes in climate models,
• sources and drivers of biases in climate models from subgrid scale parameterizations to higher level physical interactions,
• verification and intercomparison of climate model results, including new evaluation methods/metrics,
• data treatment and visualization of climate model results.

Improved reanalyses of past weather can be obtained by retrospectively assimilating reprocessed observational datasets ranging from surface stations and satellites with a up-to-date Numerical Weather Prediction (NWP) model. The resulting time series of the atmospheric state is both dynamically consistent and close to observations. The interest in extracting climate information from reanalysis is rising and creating a request for reanalysis uncertainty estimation at various temporal-spatial scales.
These research questions are adressed in the ERA-CLIM, EURO4M and UERRA projects which are supporting the development of the Copernicus Climate Change Services.

This session invites papers that:
• Explore and demonstrate the capability of global and regional reanalysis data for climate applications
• Compare different reanalysis (global, regional) with each other and/or observations
• Improve recovery, quality control and uncertainty estimation of related observations
• Analyse the uncertainty budget of the reanalyses and relate to user applications

Tropical cyclones (TCs) are devastating weather phenomena that can cause vast socio-economic impacts. Here the term TC encompasses tropical depressions, tropical storms, hurricanes and typhoons. Each TC is predominantly influenced by synoptic-scale conditions, whereas, TC activity from sub-seasonal to decadal timescales is influenced by large-scale climate variability. Advances in understanding and prediction of TC activity enable us to make meaningful TC predictions with longer lead time. Since TCs in different basins have similarities and differences in terms of how large-scale conditions modulate TC activity, comprehensive understanding of TC variability in different basins helps deepen our knowledge of TC predictability and enhances our capability for TC prediction. This session offers a unique opportunity for research and operational communities to share recent progress in climate monitoring and prediction of TCs in all basins from sub-seasonal to decadal timescales. Both prediction and process understanding studies are welcomed.