Interdecadal Variations and Causes of the Relationship Between the winter East Asian Monsoon and Interhemispheric Atmospheric Mass Oscillation

Abstract

Abstract Under the background of global warming, East Asia has been frequently affected by large-scale persistent extreme cold events in winter in recent years. As the most important circulation system affecting the East Asian winter climate, especially the temperature anomaly, the East Asian winter monsoon (EAWM) is affected by changes in semipermanent atmospheric activity centres such as the Siberian high and the Aleutian low. We found that there has been a significant positive correlation between the EAWM and Interhemispheric Oscillation (IHO). However, conspicuous interdecadal variations have occurred in the relationship between the EAWM and IHO. The relationship between the IHO and EAWM was most significant during 1979–2020, but this relationship was weak and insignificant during 1962–1978. During 1979–2020, the atmospheric mass (surface pressure) difference between the Northern Hemisphere (NH) and Southern Hemisphere (SH) during 1979–2020 was significantly reduced by 7.85% (0.75×1015 kg) compared with that during 1962–1978. Such interhemispheric redistribution of atmospheric mass (AM) has had a distinct impact on the land‒sea pressure contrast in East Asia and has intensified the connection between the EAWM and IHO. A strengthened EAWM has resulted in notable cooling and more severe winters in China. The apparent exportation of AM in the Antarctic region is an important driving factor for this interhemispheric change. The accompanying anomalous accumulation of AM in the Northern Hemisphere is linked with an increase in the pressure difference between land and sea in East Asia, resulting in intensifying correlation between IHO and the EAWM. The decadal enhancement of the IHO during 1979–2020 was closely connected with conspicuous warming in the tropical troposphere/lower stratosphere (UTLS). A seesaw pattern of anomalous air temperature and ozone between tropical and Antarctic UTLS has induced a decrease in Antarctic ozone masses and air temperature and has strengthened the polar vortex, corresponding to a decadal enhancement of interhemispheric AM imbalance.