The Transition of Stratospheric Polar Vortex Intensity: A Case Study of Winter 1987/88

Abstract

AbstractThe stratospheric polar vortex (SPV) is a key part of the stratospheric system. A better understanding of its variability and its interaction with the troposphere might help us to improve tropospheric predictability. In winter 1987/88, the SPV intensity exhibited the most significant positive transition (enhanced from weak to strong) between the early winter (November and December) and late winter (January and February) during 1979–2019. Therefore, we selected winter 1987/88 as an extreme case to analyze its stratosphere–troposphere interaction processes. Results indicate that the positive transition of SPV intensity was probably caused by the negative transition of upward planetary wave intensity entering the stratosphere, especially planetary wave‐1. We further found that the anomalous strong (weak) upward planetary wave‐1 in the stratosphere might originate from the increased (reduced) generation of planetary wave‐1 in the lower troposphere. Accompanied by anomalous SPV intensity, the positive (negative) stratospheric zonal wind anomalies were able to propagate downwards into the troposphere during strong (weak) SPV stages. And these out‐of‐phase downward propagating anomalies might have contributed to the out‐of‐phase tropospheric zonal wind anomalies between these two stages, which appeared as North Atlantic Oscillation‐like zonal wind anomalies in the North Atlantic region and similar dipole‐like anomaly mode but in the Asia‐Arctic region at 500 hPa. Moreover, we found that this downward influence of SPV anomalies can also manifest in its statistical relationship with the 500‐hPa zonal winds on simultaneous monthly scales.