Response of rainfall to land surface properties under weak wind shear conditions

Responses of rainfall trends to land surface properties (roughness length and sensible heat flux) under weak wind shear conditions were investigated by numerical simulation and idealized experiments. The results show that total amount, spatial pattern and intensity of rainfall were highly affected by the difference in sensible heat flux rather than the difference in roughness length. The initiation time for occurrence of rainfall became more delayed and the rainfall intensified as the given sensible heat flux decreased. A smaller sensible heat flux and a larger roughness length increased the convective available potential energy before the rainfall occurrence, resulting in stronger initial convection. The initiation processes affected the resulting convective structure, such that initial latent heat release occurred and remained downstream, leading to a widely spread convective structure above the cold pool. Spread and connected convection magnified the upright structure, thereby causing release of much more latent heat for ice water species and thus stronger rainfall intensity.