Distribution Characteristics Of Summer Precipitation In The East Part Of Northwest China And Its Relationship With Summer Monsoon

Monthly rainfall and rainstorm days were calculated based on daily precipitation of 175 stations during rainy seasons from 1981 to 2015.This study analyzed the spatial and temporal distribution characteristics of summer precipitation in the eastern northwest region.The results show that the spatial distribution of summer precipitation in the eastern part of the northwest region is increasing from the northwest to the southeast.1990S,it is a relatively small period of summer precipitation in the region.There is a certain consistency between the number of rainstorm days and the annual distribution of rainfall in summer.In the last two decades of 20 th Century,the spatial distribution of summer precipitation in the eastern part of Northwest China was dipole or tripole.In the 21 st Century,the turn was multipolar.The key years of inter-decadal changes are 1989,1997 and 2006.According to the position of the main rain belt,the summer precipitation in the eastern part of the northwest region is divided into 4 patterns: the northeast pattern,the southeast pattern,the Longshan pattern and the whole area pattern.The Northeast pattern not only contributes much to the summer precipitation in the eastern part of the northwest region,but also is the main precipitation anomaly in the east of the northwest region when the East Asian summer monsoon is stronger and the influence range is deep in the North inland.Using the NCEP/NCAR reanalysis data,the summer monsoon index defined by Yan is calculated and compared with the East Asian summer monsoon index defined by Li.The results show that the summer monsoon index defined by Yan is more suitable for the east of the northwest region,that is,the East Asian summer monsoon border area.The western Pacific subtropical high position is west and north,the subtropical summer monsoon is strong.The middle and high latitudes are the "west low East High" circulation situation,which is favorable for the precipitation in the eastern part of Northwest China.Based on the pseudo-equivalent potential temperature to define the North East Asian summer monsoon,the north boundary is most north of the year in late July,the zonal distribution of the north boundary is favorable to the summer precipitation in the north-east part of the north-west region,and the north boundary is more favorable to the southeast of the northwest region and the precipitation is normal or less in the whole area.The atmospheric circulation index has a certain forecast meaning for the summer precipitation in the eastern part of the northwest region.