TRMM Observation And Regional Model Study Of Precipitation Diurnal Variations In Summer Over Indo-China Peninsula And South Of China

TRMM (Tropical Rainfall Measuring Mission) satellite observations 3B42RT and 3G68averaged for June to August during 1998-2005 are used to investigate diurnal variations ofsummer rainfall over Indo-China Peninsula and South of China.Conclusions are as follows:Precipitations over flat land of Indo-China Peninsula and offshore reach their peaks at 16—19LST while at 07—10LST over the coastal areas. Rainfall peaks migrate from coastal areasseperately to the inland and offshore in the daytime, and migration from offshore to coastal areasin the nighttime is found, but from inland to coastal areas is not found. And precipitations overthe regions with terrain, such as the northwestern windward side of the Annam Cordillera, thewest of Sichuan Basin, the southeast side of Tibet Plateau reach their peaks in the early-morning,which is contrast to that in the land regions. Two areas on the windward side of the AnnamCordillera show great difference in the diurnal variation of rainfall, and the west of Sichuan Basinand the southeast side of Tibet Plateau show great difference in the diurnal variation with anyother land regions, which may lie in migration of rainfall.And then numerical simulations are made on the diurnal variation of rainfall overIndo-China Peninsula using the IPRC-RegCM V1.2. The above features are simulated reasonablywell in a control experiment with the high-resolution model. A sensitive experiment with theterrain removed over Indo-China Peninsula is conducted to examine the role of orographicforcing in the diurnal evolution of both the local circulation and rainfall patterns. The diurnalcharasterastics of low flow and precipitation change with the terrain removed. Comparing resultsfrom the two experiments, it shows that diurnal variations of rainfall in the western coastal areasof Indo-China Peninsula is influenced by land-sea contrast and terrain forcing while one in thewindward side of the Annam Cordillera is mainly caused by terrain forcing. Solar radiation andland-sea contrast maily contribute to the diurnal characterastics over the land while interactionsbetween terrain and the mean flow can modify diurnal characterastics. The orographic forcingaffects the diurnal precipitation through increasing the moisture convergence at low levels by blocking and deflecting the mean flow to change vertical velocity, cloud amount, mix ratios ofwater vapor and cloud liquid water. Terrains modify common characterastics of diurnal rainfallover the land, which causes different diurnal characterastics in the windward side of coast areas,mountains and basins.