Climate Change Characteristics And Influencing Factors Of Precipitation In The Eastern Part Of Northwest China

Based on the NCEP-NCAR reanalysis data,and the 1961-2010 monthly precipitation data of 81 weather stations in the four provinces of eastern region in the Eastern Part of Northwest China,the variation features of precipitation and the the regional climate change signal in study area(32-42oN,90-110oE)are diagnosed.The cause and effect mechanism of climate change were studied under the influence of regional main weather.The results are as follows:(1)The annual precipitation in the study area increased from the northwest to the southeast,and the annual precipitation is relatively big variation in less rain area,smaller in rainy area.In the study area east of 103oE,annual rainfall was decreasing and vice versa.The annual precipitation in the study area has a slight decline in 50 years.The precipitation decreased in spring and autumn,especially in autumn,Summer and winter precipitation increased,especially in winter.According to M-K mutation analysis,it was shown that the perception in autumn and winter mutated in 1975 and 1986 respectively.The wavelet analysis shows that the annual precipitation has a 3-year oscillation period exists and 13,17,7,18-year oscillation period exists in spring,summer,autumn and winter respectively.The REOF method was used to divide the abnormality type of summer precipitation:Shaanxi,Gansu,Ningxia and Qinghai border zone,northern and southern Shaanxi,the central Shaanxi plain and eastern Gansu,origin of the Yellow River,Hexi Corridor,eastern Qinghai,origin of the Yangtze River,Qaidam Basin,and Qilian Mountains.It showed that the border area of Shaanxi and Gansu and Qinghai and Ningxia is the most sensitive precipitation area in eastern part of Northwest region.(2)In summer,there are some differences in the circulation patterns in the rainy(less)years.In rainy years in June,Ural mountain ridge was weak,the blocking high in Lake Baikal was strong,East Asian trough and southern trough was deep.The cold air near the balkhash moved southward,intersecting with the warm moist air provided by southern trough flows,which was beneficial to the precipitation in the east of northwest China.Less rain in June years,the East Asian Trough was eastward,subtropical high was northward and eastward,Xinjiang ridge control the study area,it was hard to form precipitation.In rainy years in July,the Ural mountain ridge was weak,the northeast part of China was a high ridge,and a broad trough of low which formed in the Balkhash Lake and Lake Baikal area.West Pacific subtropical high elongated westword bring southerly flow intersect with Lake Balkhash low trough westerly flow,which conducive to precipitation.Less rain years in July.Ural high ridge was to the west,the West Pacific subtropical high elongates eastword,Xinjiang ridge was strong,in the front of Xinjiang ridge,the northwest air flow controlled this region,so it's hard to form the precipitation.In rainy years in August,Ural Mountain ridge was strong,Lake Baikal trough was deeper,East Asian trough was shallow,subtropical high extended westward,the study area was influenced by westerly and southerly,which favorable for the formation of precipitation.Xinjiang ridge controlled this area was not easy to form precipitation.Less rain years in August,Sub tropical high was eastward,the area was controlled by Xinjiang ridge and was not easy to form precipitation.Characteristics of Water vapor,the summer 700 hPa height field specific humidity and precipitation have the corresponding relation in phase,the more rainfall in summer(less)area,the higher(lower)specific humidity should be in the same period.(3)There is a good relationship between the summer rainfall over the eastern part of the Northwest China and the North Pacific Oscillation in the same period in July and pre-January.(4)When EL NINO occured in summer,the precipitation in the east part of Northwest China was less and it decreased more than 70% of the areas are mainly located in the eastern plateau-the central of eastern of Gansu-Ningxia-western of Shaanxi.(5)The western Pacific subtropical high area index,the subtropical high strength and the summer precipitation in the east of Northwest China were significantly positive correlated.The subtropical high area is larger and its intensity is stronger,The West Pacific subtropical high and its ridge point are westward,the blocking high the Balkhash Lake enhanced,The southwest monsoon enhanced the transport of water vapor,which leads to more precipitation in the eastern part of the Northwest China.