Interdecadal Changes of the Relationship between Early Summer Precipitation over Northeast China and Spring Land Surface Thermal Anomalies in West Asia

Recent studies have suggested a close relationship between early summer precipitation over Northeast China and spring land surface thermal anomalies in West Asia. However, is this relationship the same over multidecadal timescales? This study aims to identify the long-term variations in this relationship and the accompanying atmospheric circulation anomalies by using singular value decomposition, correlation analysis, and linear regression based on the ECMWF Reanalysis v5 (ERA5) atmospheric reanalysis, ERA-Land reanalysis, and CN05 gridded observations during 1961–2020 (60 yr). An interdecadal transition of the relationship between the spring surface temperature/thermal anomalies in West Asia and early summer precipitation over Northeast China occurred around 1990, and the temperature–rainfall relationship intensified after 1990. Based on the Mann–Kendall test, the study period was divided into P1 (1961–1990) and P2 (1991–2020). Further analysis indicated significant differences in the corresponding atmospheric circulation before and after the interdecadal transition. During P2, spring land surface warming in West Asia corresponded to a significantly enhanced early summer Circumglobal Teleconnection (CGT), which in turn suppressed the Northeast China cold vortex (NECV). The changes in circulation patterns further resulted in weakened moisture transport, strengthened subsidence, reduced precipitation triggering, and eventually, weakened precipitation. Additionally, results suggested that the interdecadal transition of the relationship and the changes in the corresponding atmospheric circulation may be related to the westerly jet stream. The second principal component (PC2) mode of the empirical orthogonal function (EOF) zonal wind in June over Asia demonstrated a pattern similar to that of the atmospheric circulation corresponding to land surface thermal anomalies. In addition, during P2, the PC2 mode of the westerly jet stream in June showed a strong positive correlation with the NECV, thereby suppressing precipitation over Northeast China. Consequently, the westerly jet stream may affect the transition of the temperature–rainfall relationship.