Modulation of the Stratospheric Polar Vortex on the Precipitation Dipole Mode in Southeast China During Early‐to‐Mid Winter

Abstract

In this study, we investigated the linkage between the stratospheric polar vortex (SPV) and precipitation in early and mid winter (November–January; NDJ) in Southeast China, using station observations and reanalysis data sets, and verified the linkage using numerical stratospheric nudging model experiments. The results reveal that the SPV has a weak influence on the first empirical orthogonal function (EOF1) mode of precipitation over Southeast China on the interannual timescale, while the second mode (EOF2) characterized by a dipole pattern is related to the strength of SPV with a max 0.49 correlation coefficient. The downward‐propagating SPV signal modulates a Eurasian Rossby wave train characterized by anomalous cyclonic circulation over the Ural sector and anomalous anticyclonic circulation centered near Lake Baikal, corresponding to a weakened Ural ridge and an enhanced Lake Baikal ridge. This circulation configuration alters cold‐air intrusion and contributes to the meridional precipitation dipole over southeastern China. The moisture budget diagnosis shows that this geopotential height anomaly influences the dipole pattern mainly through the vertical dynamic component. Horizontal dynamic and thermodynamic components both exhibit a monopole over southeastern China, however, their effects are opposite. Nudging experiments based on the historical SPV are conducted to disentangle the contribution of the SPV. The stratospheric nudging experiment reproduces parts of the observed circulation and precipitation‐dipole structure. Projection onto the observed EOF2 pattern shows that the ensemble‐reproducible signal accounts for approximately 10% of the simulated PC2 variance, indicating that SPV variability provides a detectable but limited contribution, while atmospheric internal variability remains dominant.