Impact Of Spring Siberian Snow Cover Anomaly On The Northern Edge Of The East Asian Summer Monsoon And Summer Precipitation In Northern Chin

The northernmost margin of the East Asian summer monsoon（NMEASM）is the northernmost position that the East Asia summer monsoon（EASM）can reach.NMEASM has obvious multi-scale variability,and well reflects the wet/dry climate variability in northern China.Predicting the location change of the NMEASM is important for understanding future East Asian climate change.However,the variability of the NMEAS M has not been studied extensively,and its underlying mechanisms have not been clarified.To explore the movement of the NMEASM and its causes,we use reanalysis datasets to evaluate the NMEASM index from 1979 to 2018.The main conclusions are as follows:（1）The NMEASM exhibits a southwest to northeast spatial distribution and reaches the northmost margin at the 40–42^nd pentad The NMEASM indicates a decreasing trend over 40years and a significant abrupt point in 2000,which is positively correlated with the Tibetan Plateau snow cover before 2000 and the Siberian snow cover after 2000 in spring.Meanwhile,the time series of precipitation over Mongolia and northern China show a significant decreasing trend during 40 years and exhibit a significant abrupt around 2000,which is consistent with the abrupt test of NMEASM in 2000.（2）The NMEASM has significant correlation between spring Eurasian snow cover.The first EOF mode of Siberian spring snow cover（interannual variation）increases the soil temperature and decreases the atmospheric baroclinicity over Mongolia and northern China after 2000.The decreased atmospheric baroclinicity induces the anticyclonic anomaly over Mongolia and northern China,which weakens the upward movement and water vapor transport.Meanwhile,the cyclonic anomaly over the Sea of Japan weakens water vapor transport.Hence,the first EOF mode of Siberian spring snow cover decreases the precipitation over Mongolia and makes the southward movement of NMEASM.（3）The second mode of Siberian spring snow cover（interdecadal variation）cause the quadrupole pattern of summer precipitation in eastern China and decreases the precipitation in the Yangtze River and northern China.The interdecadal variation of Siberian spring snow cover increases the soil temperature and decreases the atmospheric baroclinicity over Mongolia and northern China,which weakens the upward movement and water vapor transport.Meanwhile,the anticyclone anomaly on the south of the Sea of Japan is connected with the anticyclone anomaly over Mongolia and northern China,which weakens the water vapor transport and make the water vapor unable to reach Mongolia and northern China.Hence,the second EOF mode of Siberian spring snow cover decreases the precipitation over Mongolia and northern China and makes the southward movement of NMEASM.