Heavy rainfall in complex terrian: insights from a numerical model

Summary A numerical model is employed to study heavy rainfall events in complex terrain. The model uses a limited-fine-mesh grid and a nested grid, but does not utilize the same set of equations on both grids. Two similar, heavy rainfall cases are contrasted with each other and with a moderate precipitation case. Sensitivity experiments illustrate the effects of topography, synoptic forcing and diabatic heating on these episodes. Model results indicate that heavy rainfall in complex terrain requires a suitable superposition of mass, momentum and moisture fields in relation to the topography. It is the mass and momentum fields, however, which primarily control the location of heaviest precipitation. Synoptically similar events may be different in their underlying causes. The diabatic heating distribution may in some cases be essential to creating such episodes heavy rain.With 22 Figures