EGU22-7752, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Grid resolution dependency of land surface heterogeneity effects on boundary-layer structure

Stefan Poll1,2,3, Prabhakar Shrestha1, and Clemens Simmer1,4
Stefan Poll et al.
  • 1Institute for Geoscience, Section Meteorology, University of Bonn, Bonn, Germany
  • 2Institute of Bio- and Geosciences Agrosphere (IBG-3), Research Centre Jülich, Jülich, Germany
  • 3SDL Terrestrial Systems, Jülich Supercomputing Centre, Research Centre Jülich, Jülich, Germany
  • 4Centre for High-Performance Scientific Computing in Terrestrial Systems,Geoverbund ABC/J, Jülich, Germany

Land surface heterogeneity exerts a substantial impact on atmospheric boundary-layer (ABL) evolution by spatially varying the distribution and partitioning of surface energy fluxes and triggering secondary circulations. The representation of this physical process in numerical weather prediction (NWP) models is especially affected in the terra incognita as the model grid resolution approaches the length-scale of the largest eddies in the boundary layer. We explore these effects for a mesoscale strip-like land surface inhomogeneity in land cover, soil moisture or a superposition of both embedded in an elsewhere homogeneous landscape. The study is conducted with the numerical weather prediction model ICON (ICOsahedral Nonhydrostatic), using the default operational level 2.5 Mellor–Yamada turbulence closure (MY) and a large-eddy simulation (LES) configuration as a benchmark. While simulations with the default ABL scheme approach the LES reference when refining the spatial grid towards finer resolution, the model generates artificial circulations leading to ABL height oscillations when the horizontal grid resolution (∆x) approaches the ABL height (zi). The effect of these model-induced circulations on the state of the boundary layer is even present with weak thermal heterogeneity (∆H) under low background wind speed (vx) but diminishes with increasing background wind speed. The tuning of the asymptotic turbulent mixing length-scale (𝑙) in the operational ABL scheme helps in reducing the amplitude of the oscillations, thereby reducing the artificially induced circulations due to thermal heterogeneity which might act as unintentional trigger for clouds and precipitation. Based on the tuned synthetic model data from sensitivity runs, we propose a new parametrization for a 2-D 𝑙 as a function of ∆H, zi/∆x and vx, which is otherwise held as a constant in the ABL scheme.

How to cite: Poll, S., Shrestha, P., and Simmer, C.: Grid resolution dependency of land surface heterogeneity effects on boundary-layer structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7752,, 2022.


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