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.