Inter-annual Variations And Its Possible Reasons Of Spring Precipitation In The Arid Region Of The Northwestern China

In this study, using GPCP and CAMP precipitation data and NCEP reanalysis data, the spatial-temporal characteristics of arid regions of Northwest China (35°-45°N,80°E-105°E) are analyzed. Respectively the correlation between NW China precipitation and global sea surface temperatre、200hPa、500hPa and100hPa height field are analyzed. The major results are as follows:(1).Precipitation in Northwest arid/semi-arid regions is the main part of the Asia in arid/semi-arid regions, and the Precipitation have more obvious upward trend in the Spring and annual but Arid/semi-arid regions of Western Asia with the opposite situation.They are different in trend of month precipitation In arid areas of Northwest is less rainfall during the winter, but more in summer, and in arid regions of Western Asia are more in winter, less in summer. Due to affect weather systems of two areas is difference, hence, the change rate of precipitation in arid/semi-arid regions of Western Asia is obviously smaller than the arid/semi arid area of Northwest China.(2)With the high pressure of South Asia occurs earlier and development to the North, it will provide a high level of circulation background for precipitation in arid/semi-arid area of Northwest China,and conducive to the formation of precipitation. Reduction of the depth of snow cover over the Tibetan plateau in early winter conducive to late spring’s precipitation in the South of the Yangtze River,At the same time it play a catalytic role to summer’s precipitation of the most parts of the country in the East of the Qinghai-Tibet plateau.In addition, reduce of the frozen soil of the Qilian mountains and increase of the permafrost depth in Southeast of Qinghai-Tibet plateau is beneficial for spring’s precipitation in the Northwest(3)The basic circulation forms of spring’s precipitation in the Eastern part of Northwest China are low west-east high in the mid-latitude of Asia, If the ridge’s weak (strong) from Central Asia to Xinjiang, then The East Asia’s large shallow (depth),rainfall’s multiple(small),and The East Asia’s large shallow (depth) is more important for spring precipitation,while the South Pacific is the key area of precipitation of Northwest China in the same period. The significant West wind anomalies in West of range of the Black Sea, Caspian Sea, Okhotsk Sea that conducive to the formation of precipitation in arid area of Northwest China. The more Wet in North and central China, it’s more better to precipitation of arid area in Northwest China, and the water vapor is more enough in the arid region of Northwest China.(4) Sea surface temperature anomaly and the precipitation in spring of Northwest China has good related during the same period (March-May).The Sea surface temperature of Bengal, the Arabian Sea,10°-20°S India and near the Atlantic Ocean20°-3°N has significant positive effects to the Precipitation of spring in arid/semi arid area of Northwest China. Analysis of the relationship between Northwest’s precipitation in spring and sea surface temperature in early winter shows that it with the area of Southeast Pacific has a high positive correlation, and has significant negative correlation with southern South America and India Ocean fragmented region.