Physical mechanisms behind the interhemispheric teleconnection between South Pacific Meridional Mode and Bohai, Yellow and East China Seas during boreal summers of 2001–2019

The emergence of SPMM (South Pacific Meridional Mode)-BYECS (Bohai, Yellow and East China Seas) interhemispheric teleconnection after the early 2000s contributed to extreme marine heatwaves in the BYECS, yet the underlying physical mechanism remains poorly understood. We examined this teleconnection comprehensively, utilizing observational data from multiple sources, and proposed a physical mechanism involving SPMM-ITCZ (Intertropical Convergence Zone)-WPSH (western Pacific subtropical high) variabilities. The weakened ITCZ associated with a positive SPMM resulted in a weakened sinking branch to the north, consequently increasing convection and precipitation in the western Pacific (150–180°E; 9–27°N). This weakened the WPSH by stimulating a cyclonic anomaly, which promoted moisture transport and precipitation on the eastern edge, establishing positive feedback. At the western edge of this cyclonic anomaly, strong northerly wind anomalies reduced moisture replenishment and caused descending anomalies over the eastern part of BYECS. High-pressure anomalies on the western side of the northerly wind anomalies also resulted in descending anomalies over the BYECS. The inhibited upward motion and moisture replenishment jointly led to reduced cloud cover and increased shortwave radiation, thereby increasing BYECS sea surface temperature anomalies (SSTa) alongside SPMM-SSTa. This study proposed new physical mechanisms regarding with SPMM-ITCZ-WPSH interhemispheric teleconnection which is crucial to climate prediction in marginal seas.