Scale dependent land-atmosphere coupling strength in regional climate modelling

In continuous regional climate simulations, the equilibrium between land-surface and atmospheric processes plays a key role both in near surface temperature and in precipitation estimations. A too strong coupling can cause the upper soil layer to dry out in larger amounts than it supposed to, which leads to reduced precipitation and temperature overestimation in summer. The amount of available soil moisture is critical both on summer heat wave strength and on precipitation formation. The strength of coupling determines the partition between sensible and latent heat fluxes which in return influences both temperature and precipitation.

In this study we use 1-year long simulations at 50 km and at 5 km horizontal resolution to analyze the coupling strength between the land surface and the atmosphere with the WRF model. Both simulations refer to the same year and the initial and boundary conditions are given based on the ERA5 reanalysis dataset. The simulation is initialized based on ERA5 only at the beginning, then only the boundary conditions are updated to create continuous, regional climate modelling like environment. The 50 km resolution simulation covers most of Europe, while the 5 km simulation covers the Carpathian region.

The coupling strength and the effect of surface is analyzed through changing the land cover from the USGS to the CORINE one. The study will focus on the Carpathian region as local summer precipitation formation is highly dependent on local factors rather and not on large-scale weather systems. Though land-atmosphere coupling mostly affects the surface based latent and sensible heat fluxes, the resolution of the simulations affects the amount of the coupling strength through the advection.