Impacts of Spring Soil Moisture Anomalies in Qinghai-Xizang Plateau on the Summer Precipitation Variability in China

Using 1979 -2014 Global Land Data Assimilation System-the Community surface parameter data set， China regional daily observation data grid data set （CN05.1） and ERA-interim reanalyze atmospheric circulation data.To study the relationship between the abnormal soil moisture in the Qinghai-Xizang Plateau in May and the surface heat flux in June and the precipitation change in July.The results show that： （1） From 1979 to 2014， the average soil moisture in the 0~10 cm layer area in May was abnormally high years were： 2000， 2001， 2004， 2005， 2006， 2013； the abnormal low years were： 1994， 1995， 1996， 1998， 1999.Soil moisture increased after 2000.Soil moisture increased after 2000.The soil moisture in the higher Tibetan Plateau， the Three Rivers Source Region， and the southern Tibetan valley is significantly higher than in the lower years.The results passed the 90% confidence test.（2） There is a clear correlation between the abnormality of soil moisture in spring and the distribution of summer precipitation in China.When the soil is wet （dry）， from high latitude to low latitude， the relevant area is "+ - + -" （"- + - +"） banded distribution.（3） The soil is moist in May， and the sensible heat flux in the east and the latent heat flux in the west increase in June.Their combined effect strengthens the convergent circulation of the lower atmosphere and the divergence circulation of the upper layer， so that the East Asia region is controlled by the strong anticyclone circulation above 850 hPa.The 500 hPa and above in the northeast of the plateau is an anticyclone circulation， and the south and west are cyclonic circulations.This circulation field configuration makes the South Asian high pressure move eastward and the Western Pacific subtropical high pressure.（4） In July， the Huanghuai area on the north side of the Pacific High has a vertical upward movement.The warm and moist air flow converges with the dry and cold air flow on the west side of the northeast cold vortex.High-level divergence and low-level convergence are conducive to precipitation in Huanghuai area.The eastern northwestern and northern China regions are controlled by anticyclonic circulation， with strong sinking movement， dry and cold air， and insufficient water vapor transport， which is unfavorable for precipitation.