Abstract:
This paper, based on the ERA5 reanalysis dataset and the NOAA sea ice concentration (SIC) data, accurately extracted the varying annual cycle of the stratospheric polar vortex (SPV) using the Ensemble Empirical Mode Decomposition (EEMD) method. We further identified key sea ice regions associated with the interannual changes in the build-up and break-up date of the SPV, and investigated how autumn sea ice in the key region influences the evolution of SPV through both thermal and dynamic processes. Results show that there are significant interannual variations in both the SPV build-up and break-up dates, with the variation in break-up dates being more pronounced. Years with anomalously late (early) SPV build-up and early (late) break-up tend to have an anomalously strong (weak) SPV in mid-winter. Late SPV build-up is linked to warm temperature anomalies in the polar stratosphere during late winter to early spring, creating favorable conditions for SPV early break-up events. Further investigation shows a positive correlation between October SIC in the Barents Sea and the SPV build-up date, likely due to its influence on planetary wave modulation and reflected shortwave radiation in autumn. However, the statistical significance is relatively low, indicating a limited role of sea ice in the SPV build-up. Conversely, October SIC in the East Siberian Sea shows a significant negative correlation with the SPV break-up date. The primary mechanism behind this relationship is that anomalously low SIC in the East Siberian Sea suppresses the upward propagation of planetary waves. This leads to Eliassen-Palm (E-P) flux divergence anomalies, stronger stratospheric circumpolar westerlies. Thereby, SPV break-up is delayed, which is dominated by slow diabatic processes. In contrast, high SIC enhances planetary wave propagation, resulting in E-P flux convergence, weaker circumpolar westerlies. Therefore, SPV break up earlier, which is due to rapid dynamic processes.