Category‐Based Composite Analysis of Arctic Tropopause and Tropopause Inversion Layer Responses to Sudden Stratospheric Warmings

Abstract

This study investigates the heterogeneous impacts of sudden stratospheric warming (SSW) events on the Arctic tropopause and tropopause inversion layer (TIL) using ERA5 reanalysis data from 1979/1980 to 2022/2023. According to the significance of their TIL and tropopause height responses, all 50 SSW events are classified into five categories: significant major, significant minor, non‐significant major, non‐significant minor, and anomalous minor. 65.4% of major SSWs and 12.5% of minor SSWs have significant impacts on the Arctic tropopause and TIL. Notably, anomalous minor SSWs do not strengthen but weaken the TIL, and do not lower but raise the tropopause height. Building upon the established coupling mechanism between the TIL/tropopause and SSW, we analyze the role of background flow changes: stratospheric planetary wave breaking decelerates background westerlies, causing subsequent planetary waves to break at lower altitudes and amplifying both adiabatic heating that drives tropopause descent and dynamical heating that enhances the TIL. We further provide an explanation for the generation of dynamical heating near the tropopause, which arises from the coexistence of residual mean upwelling anomalies induced by planetary wave divergence anomalies at 7–12 km and residual mean downwelling anomalies induced by planetary wave convergence anomalies above 12 km. The breaking of sufficient upward‐propagating planetary waves in the stratosphere satisfies the key dynamical condition required for significant impacts on the tropopause and TIL. When stratospheric planetary wave convergence anomalies are weaker than the local planetary wave divergence anomalies, the TIL is weakened and the tropopause height rises instead.