Interdecadal changes in the asymmetric impacts of ENSO on wintertime rainfall over China and atmospheric circulations over western North Pacific

摘要

Based on data diagnoses, in this study the interdecadal changes in asymmetric impacts of ENSO on wintertime East Asian climate are investigated. It is found that the Pacific Decadal Oscillation (PDO) can significantly modulate the asymmetry in the responses of the East Asian climate to El Nino and La Nina events. In positive PDO phase the response is asymmetric with a strong anomalous anticyclone over western North Pacific (WNP) and significant positive rainfall anomalies over southern China during El Nino winters, but a weak anomalous cyclone over WNP and insignificant negative rainfall anomalies over southern China during La Nina winters. However, such asymmetric responses do not appear in negative PDO phase, with comparable amplitudes of anomalous circulations over WNP and rainfall over southern China in El Nino and La Nina winters. Further analyses reveal that the warm background of the tropical Pacific in positive PDO phase causes significant difference in the amplitudes of convection anomalies over tropical western Pacific, resulting in asymmetric responses of the WNP circulation and rainfall over southern China to El Nino and La Nina events. Nevertheless, the cold background in negative PDO phase reduces the amplitude difference between El Nino and La Nina winters. A comparable convection anomalies appear in tropical western Pacific in El Nino and La Nina winters and the asymmetric responses do not occur.