IMPACT OF LAND-SURFACE MOISTURE VARIABILITY ON LOCAL SHALLOW CONVECTIVE CUMULUS AND PRECIPITATION IN LARGE-SCALE MODELS

Numerical experiments using a state-of-the-art high-resolution mesosca le cloud model showed that land-surface moisture significantly affects the timing of onset of clouds and the intensity and distribution of p recipitation. In general, landscape discontinuity enhances shallow con vective precipitation. Two mechanisms that are strongly modulated by l and-surface moisture-namely, random turbulent thermal cells and organi zed sea-breeze-like mesoscale circulations-also determine the horizont al distribution of maximum precipitation. However, interactions betwee n shallow cumulus and land-surface moisture are highly nonlinear and c omplicated by different factors, such as atmospheric thermodynamic str ucture and large-scale background wind. This analysis also showed that land-surface moisture discontinuities seem to play a more important r ole in a relatively dry atmosphere, and that the strongest precipitati on is produced by a wavelength of land-surface forcing equivalent to t he local Rossby radius of deformation. A general trend between the max imum precipitation and the normalized maximum latent heat flux was ide ntified. In general, large values of mesoscale latent heat flux imply strongly developed mesoscale circulations and intense cloud activity, accompanied by large surface latent heat fluxes that transport more wa ter vapor into the atmosphere.