Impacts of land cover heterogeneity and land surface parameterizations on turbulent characteristics and mesoscale simulations

Abstract

The impacts of surface heterogeneity and land surface parameterization on the mesoscale processes were studied. Experiments were conducted using the Weather Research and Forecasting (WRF) model coupled with a simple (slab) land surface model (LSM), a relatively complex Noah LSM, and a land data assimilation system (LDAS) with detailed surface fields. Three heterogeneity length scales: 1, 3, and 9 km, were employed to alter land cover and land use. A series of simulations were performed over the U.S. Southern Great Plains during the summer when the soil moisture was abundant. Results indicate that both the land surface parameterizations and fine-scale surface heterogeneity affect the model simulations; and the impact of land surface parameterization is found to be more important, particularly for low frequency ($f<{10}^{-4} \mathrm{hz}$) eddies and mesoscale circulations. Substantial variations in turbulent spectra were also noted, and the energy spectra respond nonlinearly to the changes in the heterogeneous length scales. Three important conclusions emerge: (i) more detailed land surface representation reduces uncertainty in simulations of surface fluxes via improved turbulence characterization over a heterogeneous land surface, which helps improve simulations of land–atmosphere feedbacks; (ii) the impact of land surface heterogeneity on atmospheric feedbacks can be detected in the mesoscale circulations that are roughly four times of the spatial heterogeneity scale; and (iii) the land surface heterogeneity that can influence mesoscale circulations would be a function of grid spacing in the model.