TRIGGERING OF ATMOSPHERIC CIRCULATIONS BY MOISTURE INHOMOGENEITIES OF THE EARTHS SURFACE

A two-dimensional mesoscale soil-atmosphere model is used to simulate the triggering of atmospheric convection by horizontally varying soil water content. The variation is periodic with a wavelength λ between 4 and 40 km, which is considered a realistic scale for the variation of land surface characteristics. Three stages of convection can be clearly discerned: a short initial stage when convection sets in and where the size of the conective cells is determined by λ, a mature stage with well developed cells whose size is still determined by λ, and a decay/transformation stage, characterized by the formation of narrow regions of strong updrafts and wide regions of moderate downdrafts, independent of λ. Parameters relevant for the transition are given, and the importance of the feedback between soil and atmosphere is demonstrated. The dependence of convective parameters, e.g., height of the convective layer, vertical velocity and fluxes of heat and moisture on λ is investigated. The calculations of the mature stage are compared with the predictions of a linear model. © 1990 Kluwer Academic Publishers.