Modeling the Flow Response to Surface Heterogeneity during a Semi-Idealized Diurnal Cycle

Abstract

To characterize the effects of subgrid surface heterogeneity, the blending height concept has been developed as a coupling strategy for surface parameterization schemes used in numerical weather prediction (NWP) models. Previous modelling studies have tested this concept using stationary conditions with one-dimensional strips of surface roughness. Here, Large Eddy Simulations (LES) are used to examine the response of the blending height and effective surface roughness to tiled land cover heterogeneity, or a two-dimensional chessboard pattern of alternating high and low vegetation given a diurnal cycle of solar irradiance in subarctic conditions. In each experiment, the length scale of the roughness elements is increased while the total domain fraction of each vegetation type is kept constant. The effective surface roughness was found to decrease with increasing length scale of surface cover heterogeneity, which is shown to have a significant impact on estimated wind turbine power calculated from logarithmic wind profiles. In stable conditions, the blending height in cases with large heterogeneity length scales was found to exist well above the surface layer. As the behavior of the blending height has implications for coupled models, a simple model for the blending height as a function of heterogeneity length scale is introduced.

Sub‐daily rainfall intermittency: Is it really stochastic? A test at two Australian locations

“…However, presumably at any location, there are turbulent interactions of the synoptic winds with local patterns of convective uplift (perhaps related to different vegetation conditions, including albedo and surface roughness height), together with changes in the surface net radiation linked to changes in cloud cover and cloud motion. Janzon et al (2023) explored the effects of geometric 'chessboard' patterns of surface heterogeneity on air motion during the diurnal cycle. These would be super-imposed on the regular diurnal march of insolation.…”