What Controls the Strength of Convective Circulations in Real-Case Large-Eddy Simulations During FESSTVaL?

Large-Eddy Simulations (LES) are set up to complement the FESSTVaL Field Experiment on sub-mesoscale spatio-temporal variability in Lindenberg using the Icosahedral Nonhydrostatic (ICON) model in a limited-area mode. The LES represent realistic conditions in the area around the observational site and are forced by the ICON-D2 analysis and forecasts. Four nested domains are used of which the innermost one has a horizontal grid resolution of about 75 m. This presentation will focus on the sensitivity of surface turbulent heat fluxes and their spatial variability on soil moisture to explain the discrepancies between the modeled and observed sensible heat flux. In-situ measurements provide the surface heat flux representative of different land cover conditions, crops and forests, while the area-averaged flux is measured along a scintillometer path of several kilometers. Next, a series of experiments will test the sensitivity of the strength of convective circulations on soil moisture. In these experiments, the initial soil moisture is increased, decreased or perturbed in different ways to find what role the variability of soil moisture plays in setting the strength of the convective circulations. The variance of vertical velocity is then compared to the FESSTVaL measurements derived from Doppler Lidar in vertical stare mode to find how realistic the circulations in LES are. This analysis focuses on several "golden days" that include a clear-sky day, three shallow-convective days of which one developed boundary-layer rolls and two precipitating days in June 2021. The complete set of the LES covers the intensive observational period of FESSTVaL from the 7. June to 4. July 2021.