A Study on Characteristics of Precipitation and Circulation Pattern in Early Summer, Midsummer and Conventional Summer in Northeast Asia

Based on monthly Global Precipitation Climatology Project (GPCP) data from 1079 to 2015, temporal and spatial characteristics of precipitation and circulation patterns in early summer, midsummer and conventional summer in Northeast Asia are systematically investigated using empirical orthogonal function (EOF) analysis and Morlet wavelet methods.Results indicate that the conventional summer precipitation is dominated by midsummer precipitation.The interannual and interdecadal circulation variations are consistent with the characteristics of midsummer precipitation, while the mechanisms for early summer and midsummer precipitation are significantly different.Looking at the spatial distribution of precipitation, it is found that the first leading mode of early summer precipitation exhibits a "+-+" tripole pattern along the meridional direction, while an opposite pattern is found in the first leading modes of midsummer and conventional summer precipitation.Early summer precipitation demonstrates a 5-6-a period and midsummer precipitation shows a 2-3-a period.In the late 1990s, midsummer precipitation and conventional summer precipitation experienced a significant decadal change in North China and Northeast China.Further analysis indicates that early summer precipitation anomalies are mainly zonally distributed, which is partly attributed to the water vapor transport to Northeast Asia by anomalous anticyclonic circulation over the Western Pacific and partly attributed to the effects of the Eurasian Ⅱ teleconnection (EUII).In midsummer, precipitation is mainly affected by the northward extension of western Pacific subtropical high and the strengthening of water vapor transport from the Bay of Bengal and the South China Sea.Eurasia Ⅰ (EUI) teleconnection pattern and East Asia-Pacific (EAP) teleconnection pattern both are significantly correlated with midsummer precipitation in western China and the coastal area of China.Summer precipitation anomalies extend from northwest to southeast due to the effects of EUII teleconnection pattern.The effect of EAP teleconnection pattern leads to the tripole or dipole patterns of summer precipitation distribution along the meridional direction.