Dipole Pattern in Southern Hemispheric Mid-latitude and Asian-African Summer Precipitation

As the first middle and high latitude circulation mode in the Southern Hemisphere, the Antarctic Oscillation (AAO) has a zonally symmetric structure.Using the empirical orthogonal function method, this study reveals existence of another dominant mode of atmospheric circulation in the eastern Southern Hemisphere boreal summer (June-September).Different from the AAO, this mode shows a significant zonal dipole distribution, or dipole pattern.This dipole pattern accounts for more than 20% of the total variance in the regional sea-level pressure field, and shows a strong interannual variation.Further research has demonstrated that the dipole pattern is significantly positively correlated with summer rainfall in Asia and Africa, especially in South China, South Asia, and tropical eastern Africa.Analysis suggests this pattern anomaly can influence the variation of cross-equatorial flow in the Eastern Hemisphere, which can affect the transportation of water vapor into South China, South Asia, and tropical eastern Africa, and ultimately result in summer precipitation anomalies over the three regions.The dipole pattern revealed in this study is independent from the AAO, and the results of this study are not only helpful for better understanding the variation and influence of the atmospheric circulation in the Southern Hemisphere but also for examining summer precipitation variations and mechanisms in Africa and Asia.