Preconditioned Stratospheric Modulation on the Occurrence of Stratospheric Final Warmings

Abstract

AbstractStratospheric Final Warmings (SFWs) are considered to have a distinct impact on the surface weather and stratospheric ozone. Most SFWs are predominantly wave‐driven, while previous studies generally focused on the effects of tropospheric anomalous wave forcing on stratospheric wave amplification. This study demonstrates the crucial role of preconditioned stratospheric modulation on the occurrence of wave‐driven SFWs in the Northern Hemisphere, using ERA5 reanalysis. In most cases, the preconditioned stratospheric state is the key factor in determining the occurrence of both early and late SFWs. The tropospheric anomalous wave forcing cannot independently trigger most SFWs without stratospheric modulation. The proportion of anomalous stratospheric signals followed by SFWs is much higher than that of anomalous tropospheric forcing, even if the proportions of SFWs preceded by anomalous stratospheric signals and tropospheric wave forcing are similar. Additionally, about 25% of SFWs are only preceded by stratospheric modulation without anomalously strong tropospheric wave amplification.