Characteristics of Zonally Symmetric Oscillations in the Middle Atmosphere and Their Relationship With Arctic Sudden Stratospheric Warmings

Abstract

Using the zonal wind data from the Modern-Era Retrospective Analysis for Research and Applications Version 2, this study investigates the relationship between zonally symmetric oscillations (S0, wavenumber zero) in the middle atmosphere and Arctic sudden stratospheric warming (SSW) events from 2004/2005 to 2023/2024. A total of 49 SSW and 31 S0 events were identified, with all S0 events occurring within ±20 days of SSW onset. Of these, 95% of S0 events occurred within 8.9 days of the nearest SSW onset, indicating a temporal association between S0 and SSW events. We classified the S0 into four scenarios: before and during major and minor SSW events. The average peak amplitude of S0 was higher before the onset of major SSW and after the onset of minor SSW, with the average peak amplitudes reaching 25.6 and 26.1 m/s, respectively. This variation is related to the Arctic background wind field: weak westerlies before major SSWs facilitate the propagation of S0, while reversed winds during SSWs suppress its propagation. In contrast, during minor SSW events, the weakening westerlies are favorable for the propagation of S0. Among the 31 identified S0 events, 13 (42%) are likely triggered by nonlinear interactions between traveling planetary waves and the stationary planetary wave with zonal wave number 1 (SPW1), as demonstrated by Eliassen-Palm (EP) flux diagnostics and nonlinear interaction analysis. For the remaining 58% of events, other mechanisms, such as wave-mean flow interactions and momentum deposition from gravity waves and tides, may be responsible.