Impacts of a Tripolar Sea Surface Temperature Pattern Over Tropical-North Pacific on Interannual Variations of Spring Extreme Consecutive Dry Days Over Southern China

It is well known that the El Nino-Southern Oscillation (ENSO) has a profound impact on climate over southern China (SC). This study indicates that independent from the ENSO variability, a meridional tripolar sea surface temperature (SST) pattern over tropical-North Pacific in February has a close relationship with interannual variations in the frequency of spring extreme consecutive dry days (extreme-CDDs) over SC. Further analyses suggest that the tripolar SST pattern has a good persistence from February to the following spring and could influence the variations of SC extreme-CDDs through two ways. On one hand, the extratropical SST anomalies of the tripolar pattern can cause the meridional shift of the North Pacific subarctic oceanic front, resulting in a meridional dipole atmospheric pattern over the region from the North Pacific to East Asia through eddy-mean flow interaction. The meridional atmospheric pattern can influence the East Asian upper-level jet and western Pacific subtropical high (WPSH), leading to anomalous vertical motion and moisture transport over SC. On the other hand, the SST anomalies of the tripolar pattern over the tropical western Pacific can excite an overturning circulation and influence the WPSH through the Matsuno-Gill response, also contributing to anomalous vertical motion and moisture transport over SC. These physical processes are further confirmed by numerical simulations. Therefore, through the aforementioned two physical ways, the February tripolar SST pattern can influence the moisture and dynamical conditions associated with the occurrence of extreme-CDDs, consequently providing a factor and predictor for the variations of SC spring extreme-CDDs.

Automated summary

This study finds that a meridional tripolar sea surface temperature (SST) pattern over the tropical-North Pacific in February is closely related to the interannual variations in the frequency of spring extreme consecutive dry days (extreme-CDDs) over southern China (SC), independent from the El Nino-Southern Oscillation (ENSO) variability. The tripolar SST pattern can influence the variations of extreme-CDDs in SC through changes in atmospheric circulation patterns and the circulation in the tropical western Pacific.