Characteristics and mechanism analysis of dipole precipitation in Northeast China

This study examines the interannual variability of the summer precipitation dipole pattern over northern eastern China, utilizing precipitation data and atmospheric reanalysis data from 1961 to 2020, along with an analysis of its underlying influencing mechanisms. Results indicate that the second mode of empirical orthogonal function (EOF2) mode of summer (June–August) precipitation in Northeast China presents a dipole pattern with opposite trends in the north and south, and its time series (PC2) demonstrates signifcant interannual variations. The South-North dipole pattern in summer precipitation over Northeast China are signifcantly correlated with the tropical Pacific sea surface temperature, Arctic sea ice, and Eurasian snow cover in the preceding spring (March–May) on an interannual scale. In the preceding spring, the increase in sea surface temperatures in the eastern equatorial Pacific, coupled with a decrease in temperatures in the western equatorial Pacific, stimulated the East Asia-Pacific and Eurasian teleconnections by weakening the Walker circulation near the equator. This alteration positioned a cyclonic center over Northeast China, subsequently influencing the dipole pattern of precipitation in the region. Furthermore, the anomalies in European snow cover and Arctic sea ice can lead to an increase in albedo and a decrease in upward heat flux, causing the lower atmospheric temperature to drop and persist into the summer. This causes the atmospheric Rossby wave to propagate eastward in the middle and high latitudes, promoting precipitation in the northeast through the occurrence of negative potential height anomalies over the Far East.  These conditions influence the anomalies in the atmospheric circulation over the Eurasian continent, regulate moisture transport and vertical motion, and collectively contribute to the dipole pattern of summer precipitation in Northeast China over the past 60 years, with opposite trends in the north and south.