(1) Investigating Arctic Multilayer Clouds with K-means Clustering (2) Simulating the size sorting of hydrometeors with P3 microphysics in a supercell case of the RELAMPAGO-CACTI campaign (3) Ein Experiment mit der senseBox zur Aufzeichnung von Wetterphänomenen für Physiklehramtskandidat:innen (4) Assessing the aerosol direct radiative effect - a radiation multiple call scheme implemented to ICON-ART

Global warming is known to weaken both the convective mass flux and the Walker circulation. Yet, in the past decades, the convective mass flux has been weakening while the Pacific Walker circulation has actually been strengthening. To investigate this discrepancy, we conducted a series of prescribed sea surface temperature (SST) experiments to separate the effects of global warming from changes in SST patterns. The tropical-mean convective mass flux weakens in proportion to global warming, largely unaffected by SST pattern changes. Conversely, the Walker circulation response is sensitive to SST pattern changes, weakening with global warming if zonal SST contrast decreases or increases below a certain threshold and strengthening if the increase in SST contrast exceeds that threshold. Thus, the Walker circulation might continue to strengthen if the SST pattern effects dominate. Our results indicate that the weakening of convective mass flux alone is insufficient for projecting the Walker circulation response.
 
Recognizing the impact of historical SST pattern changes, we further investigate potential mechanisms behind the changing the tropical Pacific SST pattern during the historical period. Recently, the tropical Pacific has been cooling, particularly in the eastern basin – a trend that coupled global climate models under historical forcing notoriously fail to capture. Our coupled model intercomparison study suggests that Southern Ocean surface cooling, another feature absent in historical simulations, has driven the eastern tropical Pacific cooling. This Southern Ocean-tropical Pacific connection appears in models only with sufficiently strong stratocumulus cloud feedback.
 

The turbulent mixing of clouds with their environment decreases cloud amount, and hence the ability of clouds to reflect solar radiation. Because the mixing increases with the droplet and hence aerosol concentration, this interaction is known to affect the role of clouds in the climate system, although its magnitude is hard to constrain. In this talk, I will review several mechanisms by which the droplet concentration affects the turbulent mixing of clouds and their environment, and discuss some associated problems. Ultimately, I will use ensembles of large-eddy simulations to derive a heuristic model by which the effect of aerosol-mediated mixing on clouds can be assessed. 

(1) Convective storms in a changing climate (2) tbd (3) Analysis and correction of MJO related errors in subseasonal ECMWF ensemble forecasts (4) tbd
 

(1) tbd (2) Serial clustering of multiple impact-related hazards in Germany (3) tbd (4) tbd

 
 

At temperatures between -40°C and 0°C, clouds can be mixed phase, so called because they consist of a mixture of both liquid cloud droplets and ice crystals. This type of cloud is especially poorly represented in climate models. One of the reasons is that both hydrometeors are assumed to be homogeneously mixed in global models, but observations show that ice and liquid are heterogeneously mixed and exist in separate "pockets". This difference in the 3-dimensional spatial distribution of ice and liquid is important to assess and quantify precipitation, cloud processes, radiative properties, and consequently their impact on climate change. The present study aims to better characterize mixed phase clouds and especially the spatial distribution of the thermodynamic phase and understand how meteorology, air parcel transport and aerosols impact it.
 
We defined a parameter to describe the spatial distribution of liquid and ice phases within mixed-phase clouds from observations from the space-based lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarisation). We spatially and temporally collocated the satellite measurements with reanalysis retrievals of aerosol concentration and meteorological parameters from ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis v5) and MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) and then applied a multi-linear linear regression fit to quantify the influence of the external parameters on the spatial distribution of the cloud phase up to first order. A second part of the study focuses on ground-based measurements from the North Slope Alaska Station (NSA), where the transport of air parcels is analysed according to cloud type.
 
Focusing on the Arctic region, the results show that temperature is the most important parameter influencing the liquid-ice interface: for example, clouds with a temperature above 265 K have seven times more liquid-ice interfaces and are more homogeneously mixed than clouds with a temperature below 253 K. Black carbon concentration are also important parameters to describe the phase distribution. At NSA, clouds associated with higher transport may be more heterogeneously mixed. The results could be used to refine the parameterisation of clouds in models and their impact on climate change. 

(1) tbd (2) Innovative climate indices to support adaptation strategies at local level - a participatory approach (3) ICON simulations for Swabian MOSES (4) The TEAMx (Multi-scale transport and exchange processes in the atmosphere over mountains – programme and experiment) observational campaign

Since October 2023, a high-resolution urban climate analysis – based on the air flow model FITNAH-3D has been available for Heidelberg, which covers the city area with a spatial resolution of 5 x 5 m.  The results can be used to derive statements about the current microclimatic state and the expected change in the quality of living and local climate comfort for citizens and residents. 
The new screening tool (the so-called climate scanner) allows the display of microclimatic effects of individual measures (tree planting, green facades, etc.) or changes to the position of existing buildings "instantly" via a GIS-interface - without the need for high-performance computing. This enables a fact-based assessment of climate adaptation measures even before the planning process, which in turn prevents costly subsequent adjustments.
The tool is based on an artificial intelligence which is built on a neural network that combines the results of the Heidelberg urban climate analysis with a large number of different urban climate analyses in Germany.

(1) Physical constraints on the stratospheric injection of trace gases from wildfires (2) tbd (3) Assessing the Impacts of Hailstorms in a future climate - first results (4) tbd

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(1) tbd (2) Impacts of Hailstorms on agricultural products (3) tbd (4) tbd