Linkage between the Asian-Pacific Oscillation and winter precipitation over southern China: CMIP6 simulation and projection

Based on the simulations of 30 CMIP6 models, this paper evaluates their performance in simulating the linkage between the winter Asian-Pacific Oscillation (APO) and precipitation over southern China (SC). Results show that 12 out of the 30 models can reproduce well the observed inverse relationship featuring a positive APO phase corresponding to a decrease in SC precipitation. Associated with the positive APO phase, an anomalous anticyclonic circulation dominates the southern part of Asia in the upper troposphere, and an anomalous cyclonic circulation prevails particularly in the lower troposphere of the South China Sea and the Malay Archipelago. Accordingly, the East Asian westerly jet (EAWJ) shifts northward, and low-level northeasterly anomalies appear over SC, which yield anomalous descending motion and water vapor flux divergence in SC, respectively, hence decreasing the in-situ precipitation. Using the ensemble of the 12 models, the future relationship between the winter APO and SC precipitation under the SSP5-8.5 scenario was further projected. The projection indicates that the APO connection with SC precipitation will still be significant, but weakened slightly, during the second half of the 21st century as compared to the present. Such a weakening may result from the weaker linkage between SC precipitation and the meridional displacement of the EAWJ.