Evaluation and Projection of the Influence of the August Asian–Pacific Oscillation on Precipitation in Northern Xinjiang Based on CMIP6 Simulations

Based on CMIP6 model data and reanalysis data, two multi-model ensemble means—the “best” model ensemble (BMME) and the negative correlation ensemble (NCE)—were derived from 30 models to simulate the August Asian–Pacific Oscillation (APO) and the influence of the August APO on September precipitation over northern Xinjiang (NXPI). The results show that BMME performs better than individual models in simulating the eddy temperature in August. Overall, the BMME-simulated APO intensity shows a general decreasing trend from 2015 to 2100. Based on NCE, regressions of the precipitation and 850-hPa wind fields onto the APOI reproduce spatial patterns similar to the observations under the historical scenario. Furthermore, the NCE-simulated correlation between APO Index (APOI) and NXPI remains steadily negative during 2021–2040 under both SSP2-4.5 and SSP5-8.5 scenarios, but the negative correlation weakens significantly over the subsequent 60 years. This may be related to the southeastward shift of the negative geopotential height anomaly center over East Asia.