The Analysis of Atmospheric Circulation and Water Vapor Conditions of Precipitation over the Heihe River Basin

It is of great significance to understanding deeply mechanism of precipitation and estimating accurately amount of precipitation. The purpose of this work is to explore the atmosphere effects on the precipitation over the Heihe river basin. Based on NCEP/NCAR re-analysis dataset with the resolution of 1° × 1° and 25° × 2.5° over the period 2000-2006 and monthly precipitation from 15 stations for the same period, we investigated the vertical circulation and vapor conditions for the local-scale and further explore large-scale atmospheric circulation patterns for the rainy years and less rainy years. The comparative analysis results show that for both kinds of years, the water vapor all are net inflow averaged from June to September. However, there are notable differences in western and south boundary. In the western boundary, the inflow of vapor for the rainy years is more than that for the less rainy years. In the south boundary, there is a net inflow of vapor in the rainy years. Whereas there is a net outflow in the less rainy years. Besides, one more important point is that local ascending motion which is predominantly meridional over the Heihe river basin. Its range, position, and intensity have remarkable differences in the rainy years and less rainy years. The maximum vertical velocity is 1.2 cm/s for the former, and that for the latter is only 0.8 cm/s with the difference of 0.4 cm/s. This phenomenon is discovered for the first time in this region. Furthermore, more/less precipitation corresponds well with the higher/lower Qinghai-Tibet plateau temperature, stronger/weaker 100hPa high-pressure of the Qinghai-Tibet plateau, and stronger/weaker westerly jet. The interaction of these systems aforementioned can make more precipitation mainly due to more water vapor inflow and stronger converging-ascending motion for the rainy years. The opposite is the case for the less rainy years.