Change Of Precipitation And Synoptic Weather Typing Over Xinjiang In The Last 50 Years

Under the background of global climate change,the research on the change of precipitation and the weather that will generate heavy rains in Xinjiang is of great scientific significance.In this thesis,based on the daily precipitation data of 47 meteorological stations during 1961-2013 in Xinjiang,the temporal and spatial distribution characteristics ofprecipitation over Xinjiang were analyzed by the methods of EOF and REOF.The results showed that the precipitation over Xinjiang existed a trend of continuous growth and turned into a wetter period from 1987.Summer contributed most to the annual precipitation,leading the spatial distribution and the trend of annual precipitation.The precipitation over Xinjiang was on the rise especially the northwest region.The four vector fields of EOF showed the consistency of summer precipitation variation all over the Xinjiang region.The obstruction of the Tianshan Mountains caused the difference of precipitation between southern and northern Xinjiang.There were inverse changes in summer precipitation between eastern and western Xinjiang,also between the Tianshan Mountains and the rest areas.REOF results further suggested the sensitive areas of summer precipitation in Xinjiang,which can be divided into five climatic sub-regions.The annual precipitation in region 2 was the largest,while the growth of the increasing tendency in region 5 is the fastest.The self-organizing map(SOM)technique was applied to the Japanese 55-yearReanalysis(JRA-55)daily mean-sea level pressure(SLP)data from May to September during 1961-2013 to objectively identify synoptic SLP patterns over.the Xinjiang region.A total of 35 different SLP patterns were identified.Analysis of precipitation associated with each SLP pattern revealed that the large precipitation events were related to frontal cyclone and cold front ahead of the surface high pressure that happened mostly in May,July and September,especially over northern Xinjiang.Annual precipitation contributions from each SLP pattern were isolated to reveal that half of the annual mean precipitation over Xinjiang comes from only 13 of the 35 identified synoptic patterns,highlighting the importance of studying Xinjiang precipitation on an event-by-event basis on a daily time scale.NAO is one of the important factors of the interannual variation of precipitation over Xinjiang.The NAO index was negatively correlated with annual precipitation over Xinjiang,and significantly negatively correlated with annual increase of precipitation.In the abnormal years of NAO,it affected the precipitation over Xinjiang by controlling the transportation of water vapor in addition to the movement of surface weather systems and large-scale circulation at high altitude.Therefore,synoptic weather typing prior to the study in the variation of NAO index and large-scale circulation in domain area is very necessary in the research and prediction of precipitation over Xinjiang.