High resolution Large Eddy Simulations of the convective boundary layer over idealized land surface heterogeneities

Absorption, transformation and release of incoming solar radiation as turbulent heat into the atmosphere is critical for earth's energy balance. However, there is a lack of knowledge of the governing factors of the associated turbulent fluxes. Especially the influence of land surface heterogeneities is uncertain, as often only one-dimensional measurements are available. Finding an interrelation of the surrounding terrain to the turbulent fluxes is therefore not possible. This might be the explanation for why measured fluxes often cannot be reproduced with common calculation methods.

Thus, the objective of our study is to investigate the impact of surface heterogeneities on turbulent surface fluxes by performing idealized Large Eddy Simulations of a convective boundary layer over heterogeneous land surfaces under varying conditions. The simulations are run with the Parallelized Large-Eddy Simulation Model (PALM), covering a 10 km x 10 km domain with cyclic boundary conditions. The horizontal resolution is 5 m, the vertical resolution is 2 m near the surface and is increasing with height. The simulation period is one day. The scenarios differ in initial wind profiles, radiation, soil moisture and the type of surface heterogeneities. Output variables are averaged over 5 minutes.

By means of these highly resolved simulations, an encompassing three-dimensional analysis of the turbulent surface fluxes and their governing factors could be carried out, enabling the development of improved methods for calculating turbulent fluxes.