Spatial Distribution Of Atmospheric Water Vapor In Summer Over The Tibetan Plateau

By using the radiosonde data from14sounding stations, monthly mean surface temperature data and NCEP/NCAR reanalysis data over the Tibetan Plateau (TP) from1979to2008, the temporal and spatial distribution of summer water vapor (WV) content over TP and the factors affecting abnormal vapor such as circumfluence, etc were analyzed. The relationship between the atmospheric WV and precipitation in summer is analyzed and the meteorological factors affecting the summer precipitation conversion efficiency (PEC) are discussed based on the monthly mean precipitation data of83stations. Finally, the atmospheric WV calculated by NCEP/NCAR and ECMWF reanalysis data is compared with the atmospheric WV calculated by the radioronde data. The specific conclusions are as follows:1) The TP summer WV decreases with increasing altitude, with the largest value area observed in the northeastern part of the TP and the second largest value area in the southeastern part of the TP, while the northwestern part is the lowest value area. The summer precipitation decreases from southeast to northwest. On the whole, the TP summer WV shows increasing trend and there is less WV before the mid1990s while more after the mid1990s.2) In the recent30years, the net WV flux is positive always over the whole TP, southern TP and northern TP. The summer WV and the zonal WV flux have a very close connection over the whole TP and the southern TP that the summer WV is more in the years with the more zonal WV flux. The summer WV and the net WV flux have a very close connection over the northern TP that the summer WV is more in the years with the more net WV flux.3) In the years with more (less) summer WV, the WV flux is convergence (divergence), the net WV fulx is more than normal, the potential height is negative (positive) anomalies in the low level TP but positive (negative) anomalies in the high level TP, and the surface temperature is higher (lower).4) The summer WV presents two main patterns based on the EOF analysis:the whole region consistent-type and the north-south opposite-type. The north-south opposite-type of the summer WV is similar to the first EOF mode of the summer precipitation and both of their zero lines are located to the north of Tanggula Mountains. The summer precipitation is more (less) in the southern (northern) TP in the years with the distribution of north lack of the summer WV while south abundant, and vice versa.5) The summer PEC over the TP is between3%and38%and it has significant spatial difference in summer, which is obviously bigger in the southern TP than that in the northern TP. The summer PEC also shows the North-South opposite pattern which is similar to that of the summer WV and the summer precipitation.6) The convergence (divergence) in the low levels and divergence (convergence) in the high levels both are stronger than normal in the southern (northern) TP, the net WV flux is more (less) than normal in the southern (northern) TP, and the upward motion is stronger than normal in the southern TP, while weaker in the northern at500hPa when the south part of the TP of high summer PEC but the north of low summer PEC.