A Numerical Study of Atmospheric and Soil Boundary Layers

Abstract

A numerical model of the atmosphere-soil boundary layer was developed which simulates heat and moisture exchange between the atmosphere and the soil. The atmospheric and soil equations are solved using the physical conditions at the atmosphere-soil interface, i.e., energy and water mass conservation and the local thermodynamic equilibrium of temperature and humidity. Quasi-stationary layers were assumed in both the atmosphere and the soil near the interface. The depth of these layers was determined by the scale analysis of various transport processes in the atmosphere and in the soil. Two calculations, which were based on different assumptions for the eddy diffusivity in the Ekman layer, were compared. The temperature calculated by use of an eddy diffusivity interpolated by Hermite polynomials is in good agreement with observations. Both examples studied predicted the wind velocity weaker than the observed, especially during the night. The numerical model thus developed was applied to the study of energy balance on the soil surface with specific concern for the wetness of the soil. The model simulated the clearly distinct characteristics of the energy balance depending on the wetness of the soil. If the surface is sufficiently wet, most of the net radiative energy is transformed to latent heat released into the atmosphere, whereas for the soil with deficient water the latent heat becomes negligible and most of the net radiation is transformed into sensible heat. The results of the calculations are shown to compare favorably with the observations.