Enhanced Relationship Between Stratospheric Sudden Warming and the Madden–Julian Oscillation in Recent Two Decades

Previous studies have identified substantial changes in Madden–Julian Oscillation (MJO) activities and associated extratropical responses in recent decades. However, changes in the stratospheric impacts of the MJO, in particular on sudden stratospheric warming (SSW) events, remain to be elucidated. This study investigates the decadal variation in the MJO-SSW relationship, which suggests that, in the epoch of 1980–1999 (E1), there is an absence of systematic MJO activity preceding SSWs for all MJO phases. Conversely, during 2000–2020 (E2), a robust phase-locked relationship between MJO phase 7 (P7) and the subsequent SSWs is observed. Concurrently, E2 has seen an amplified vertical planetary wave pulse following P7, resulting in a maximum warming of the Arctic stratosphere exceeding 5°C. The results suggest a pronounced intensification of the MJO-SSW relationship in the past two decades, probably due to the prolonged duration of MJO-related enhanced convection during P7 and the shifts in the extratropical basic state.