The Nonlinear Response Of The Asian Summer Monsoon To ENSO

Using the 850hPa average wind field in summer and the SST data of GISST in 53 years, and based on the nonlinear canonical correlation analysis, we get the nonlinear response of the Tropic Summer Monsoon and the East-Asian Summer Monsoon to ENSO. The switch of the nonlinear relationship between the summer monsoon and ENSO in recent 53 years is fixed in 1976. Then the relatonship between ENSO phases and the Walker circulation, Hadley circulatition in different periods pre- and post-switch is researched. The results show:The tropical summer monsoon responsed to the ENSO SSTA index is nonlinear. Compared with the El Nino, in La Nina, the circle centers move westward and southword, and the intensity of the circulation has large anomalous. When the SSTA changed in the positive or negative phases, the nonlinear character is behaved in the intensity; while it changing from positive (negative) to negative (positive), both the intensity and the circulation represent nonlinear. The tropical summer monsoon responsed to ENSO as extracted by the NLCCA projection can be separated into a linear and a nonlinear component, the linear accounts for 67.45% and the left is occupied by the nonlinear component. In summer, the anomaly circulations in the Bey of Bengal-Westward of the Middle—South Peninsula and the west of Philippines Archipelago are arisen by the nonlinear component.The East-Asian summer monsoon responsed to ENSO is also nonlinear, and similars with the nonlinear response of the tropical summer monsoon. In La Nina, the circle centers move westward and northword, and the intensity of the circulataton has large difference, because the wind on land in La Nina is stronger than in El Nino, and opposition on the ocean. The same as the tropical summer monsoon, when the SSTA changed in the positive or negative phases, the nonlinear character is behaved in the intensity; while it changing from positive (negative) to negative (positive), both the intensity and the circulation represent nonlinear. The East-Asian summer monsoon responsed to ENSO as extracted by the NLCCA projection can also be separated into a linear and a nonlinear component, the linear accounts for 61.89% and the left 38.11% is occupied by the nonlinear component. In summer, the anomaly circulations in the east coast of our country and South China are arisen by the linear components, and the anomaly circulations in India Peninsula and west Pacific are arisen by the nonlinear one.The switch of the nonlinear relationship between the summer monsoon and ENSO in recent 53 years is fixed, by caculating running correlation between the first output PC in NN models and 11-years running average of the nonlinear time series, in 1976. Then the relationship between ENSO phases and the Walker circulation, Hadley circulation in different periods pre- and post-switch is researched. By the analysis of the perpendicularity cieculation, we find that the nonlinear responses strengthen in the metaphase in 1970s. The most important reasons that may make the nonlinear response are in different periods post- and pre-switch, in the cold and warm phases, the asymmetry of Walker cieculation becomes larger, then the downdraught of Hadley circulation in the north hemisphere moves northword and the intensity becomes stronger.