Recent Winter Precipitation Changes over Eastern China in Different Warming Periods and the Associated East Asian Jets and Oceanic Conditions

Abstract

lobal-mean surface temperature has experienced fast warming during 1985-1998 but stabilized during 1999-2013, especially in boreal winter. Climate changes over East Asia between the two warming periods and the associated mechanisms have not been fully understood. Analyses of observation and reanalysis data show that winter precipitation has decreased (increased) over southern (northeastern) China from 1985-1998 to 1999-2013. Winds at 300 hPa over East Asia strengthened during 1999-2013 around 30°-47.5°N but weakened to the north and south of it. This change pattern caused the East Asian polar front jet (EAPJ) and the East Asian subtropical jet (EASJ) to shift, respectively, equator-ward and pole-ward during 1999-2013. Associated with these jet displacements, the Siberian High enhanced and the East Asian trough shifted westward. The enhanced Siberian High strengthened the East Asian winter monsoon and weakened southwesterly winds over South China Sea, leading to precipitation decreases over South China. The westward shift of the East Asian trough enhanced convergence and precipitation over northeastern China. A combination of a negative phase of the Interdecadal Pacific Oscillation and a positive phase of the Atlantic Multi-decadal Oscillation during 1999-2013 resulted in significant tropospheric warming over the low- and high-latitudes and cooling over the mid-latitudes of East Asia. These changes enhanced the meridional temperature gradient and thus westerlies over the region between the two jets, but weakened them to the south and north of it, thereby contributing to the wind change patterns and the jet displacements.