The Tibetan Plateau, absorbing intense solar radiation, serves as a massive elevated heat source for the atmosphere, helping energize the summer monsoon. In the Asian monsoon domain, besides the Tibetan Plateau there are many less remarkable mountain ranges (~1. 5 km in height). Since they are narrow in width (500 km or less), they are called mesoscale mountains to distinguish them from the massive Tibetan Plateau. While orographic lifting effect on rainfall is well known, the effect of mesoscale mountains on the Asian summer monsoon has rarely been discussed in the literature, because of inadequate observations. In this paper, a suite of high-resolution satellite measurements is used to investigate the effects of these mesoscale mountain ranges, especially the Annam Cordillera over the Indo-China Peninsula, on the summer monsoon of the South China Sea (SCS). The Satellite datasets used in this paper include: QuikSCAT surface wind velocity from August 1999 to August 2005 on a 0.25° grid; Tropical Rain Measuring Mission (TRMM) SST on a 0. 25° grid and TRMM Precipitation Radar (PR) surface rainfall on a 0.5° grid, both from January 1998 to August 2005; Special Sensors Microwave Ima-ger (SSM/I) rainfall and surface wind velocity from July 1987 to December 2004 on a 0.25° grid. The monthly cli-matology is constructed by averaging over the available period for each dataset and the discussion in this paper is limited to these multi-year climatologies. Annam Cordillera is a mountain range that rises above 500 m and runs in a south-north direction on the east coast of Indo-China Peninsula on the Vietnam-Laos/Cambodia borders. In summer, the QuikSCAT's summer wind climatology indicates that the southwesterly wind velocity reaches a maximum off the southeast coast of Vietnam. This coastal wind jet is also present in SSM/I product As the southeasterly winds approach the mountain range, they are blocked by this mountain range. At the southern tip of this mountain range, on the other hand, winds rush through, forming the strong coastal wind jet. The TRMM's summer SST climatology shows that the maximum coastal cooling takes place off the southeast coast of Vietnam, coinciding roughly with the speed maximum along the coast and forming a cold SST filament. The cold filament, however, is obviously displaced to the north of the wind jet, indicating that the coastal upwelling induced by the coastal wind jet and other ocean dynamics probably play an important role. The TRMM-PR's summer rainfall climatology shows that as the southwest monsoon impinges on the narrow Annam mountain range, moisture-laden air is forced to rise causing intense convection on the windward side, while the mountain range entails a rain shadow on the leeside and off the east coast of Vietnam. The merged SSM/I-gauged rainfall climatology is very similar to the TRMM-PR climatology in spatial distribution, reaffirming the orographic effects on the intense convection on the foothill of the Annam Cordillera. In addition, the coastal cold filament induced by the wind jet also acts to suppress the convection above, punching a hole off the coast. Current state-of-the-art GCMs have a typical grid of 2. 8°and do not adequately resolve these narrow mesoscale mountains. Serious underestimation of these mesocale mountains is probably the major reason why GCMs have serious bias in their simulations of SCS summer monsoon.
mesocale mountainsthe South China Seasummer climatehigh-resolution satellite observations
国家科技期刊平台
NSTL
万方数据
维普
