The Spatial Character Of Summer Precipitation In Tibet Plateau And The Water Vapor Transport Around It

The summer precipitation data of 97 stations from 1961 to 2005 is used to analyze the spatial character of summer precipitation in Tibet Plateau by REOF (Rotated Empirical Orthogonal Function). The water transport character for every precipitation distribution pattern and flood years and drought years in Tibet Plateau is explored by using correlation and composite analysis. On the basis of statistic diagnose, sensitive experiments are carried out on the impact of water flux and circulation on summer precipitation for typical drought year 1997 and typical flood year 1998 in Tibet Plateau by using RegCM3( Regional Climate Model 3 ). At last, the initial condition of the model is replaced by GPS observational data of 19 stations in Tibet Plateau in order to improve the simulation results. Four conclusions are received as follows:(1) The summer precipitation in Tibet Plateau can be divided into four patterns: the southeast, the northeast, the south oriented and the north oriented. The first pattern is the most important of the summer precipitation.(2) The southeast precipitation contributes most to the summer precipitation in Tibet Plateau. The water vapor and circulation in favor of southeast precipitation also affects the whole summer precipitation greatly. The comparison between flood and drought years further shows that, when the water transport from Bay of Bengal and the South Sea to the north and from the west Pacific to the west strengthens, the circulation pattern in East Asia from the low latitude to the high latitude is"+ - +", together with Ural blocking high is abnormal high, the summer precipitation in Tibet Plateau will be more than normal. In other wise, the summer precipitation in Tibet Plateau will be less than normal.(3) The Regional Climate Model (RegCM3) has some simulation ability for summer precipitation in Tibet Plateau, but the simulation precipitation is much bigger than the observational data. The sensitive experiment verified the above statistic diagnose results. For the typical drought year 1997, when the specific humidity of the Bay of Bengal, the South Sea and the west Pacific are enlarged gradually from the edge to the center, and the geopotential height for the area of the south of Ural is enhanced by 40gpm, the summer precipitation in Tibet Plateau will increase. For the typical flood year 1998, when the specific humidity of the Bay of Bengal, the South Sea and the west Pacific are minished gradually from the edge to the center, and the geopotential height for the area of the south of Ural is weakened by 40gpm, the summer precipitation in Tibet Plateau will decrease.(4) The description ability of the initial condition of the RegCM3 for every element in Tibet Plateau is enhanced by using the GPS observational data. The simulation results are better improved than before. The change of initial condition influences the precipitation of Tibet Plateau much greater than other areas.