A DIPOLE MODE OF MONSOON RAINFALL IN HIMALAYA AND SOUTHERN PENINSULAR INDIA SUBCONTINENT
南亚季风降水的双极振荡*

A north-south spatial reversal of monsoon rainfall in Indian subcontinent has been identified.This dipole-like pattern displays an evidence of century variability with two turning points occurred around 1764 and 1876.The 1764 point represents a shift in monsoon rainfall in Northern India from decreasing to increasing while the 1876 point is from increasing to decreasing.On the contrary,in Southern Indian the 1764 turning point indicates a shift in monsoon rainfall from increasing to decreasing while the 1876 point from decreasing to increasing.The identification of this spatial reversal clarifies the former confusion existed between Indian monsoon rainfall and global warming.Our results show that the gross features of the monsoon rainfall in Southern India(or Northern India) are similar(or reverse) to the Northern Hemisphere temperature on centennial time scale over the past 300-year,which implies that the monsoon rainfall in Southern India(or Northern India) will increase(or decrease) during the coming century as greenhouse gas concentrations continue to rise.We inferred that the changes in the Northern Hemisphere temperature might have caused the variation of the cross equatorial flow that is responsible for the dipole-like monsoon rainfall variability.However,the mechanism of monsoon is so complicated that there are still many aspects need to be understood.For example,does the dipole in the tropical Indian Ocean connect with the dipole-like mode of the Arabian Sea branch and the Bay of Bengal branch of the southwest monsoon circulation? We hope that this study would provide a new insight into the study of southwest monsoon.