Numerical Examination of the Diurnal Variation of Summer Precipitation over Southern China

抄録

Diurnal variation of precipitation is frequently observed over southern China in summer. We investigate it using the regional version of the nonhydrostatic icosahedral atmospheric model (NICAM), with particular focus on the interactions among land, cloud, and radiation processes. The NICAM almost exactly reproduces the diurnal variation of precipitation but slightly overestimates its amplitude. The simulated spatial distribution of precipitation is very similar to that observed by the Tropical Rainfall Measuring Mission 3B42 product. Precipitating region propagates inland from the coast during 14-20 LT.
We perform sensitivity experiments to study the effects of surface conditions, cloud, and radiation interactions, and the results are as follows. 1) When volumetric soil moisture is reduced, surface temperature increases and surface evaporation decreases. Water vapor inflow increases owing to enhanced land-sea contrast; however, the decrease in surface evaporation counteracts this increase, thus decreasing precipitation. 2) When cloud amount is reduced, net downward radiation and surface temperature increase. Precipitation does not appear to vary with cloud conditions.
The zone of the horizontal convergence of water vapor flux propagates inland in the afternoon, although local evaporation has a greater impact than water vapor inflow on the diurnal variation of precipitation.