Synergistic Effects of Orography and Surface Fluxes on Moist Convection Initiation

Using large eddy simulation (LES), we examine the synergistic surface heterogeneity effects of orography and surface heat fluxes on moist convection initiation. We prescribe analytic, multiscale two-dimensional orography inversely transformed from a radially averaged power spectrum of -3 (where is wavenumber) in the wavelength range from 32 to 0.2 km. For the case in which the spatial distribution of surface sensible heat flux is in phase with the -3 spectrum orography, precipitating, deep moist convection rapidly develops within 3.5 h into the model integration from 1100 local time. To isolate each effect, the collocated, -3 spectrum orography and surface heat flux field are separately employed with 0 spectrum (homogeneous) surface flux field and flat terrain, respectively. The effect of the collocated orography and surface flux forcings is much more than a simple sum of those of the separate forcings. The deails on the synergsistic effects of the two collated surface forcings will be presented.