Journal Article

First Observation of Dominant Quasi‐Two‐Day Wave With Westward Zonal Wavenumber 3 at the December Solstice During Austral Summer: Links to Persistent Winter Stratopause Warming

Dou, Xiankang, Gu, Sheng‐Yang, Wei, Yafei, Liu, Yuxuan, Chen, Hao, Qin, Yusong

2025

Overview

During the 2023/2024 austral summer, the quasi‐two‐day (QTDW) with westward zonal wavenumber 3 (W3) abnormally reached its maximum amplitude at the December solstice (22 December 2023) for the first time in 20 years of Aura Microwave Limb Sounder observations, while the strongest event during austral summer usually occurs ∼2–6 weeks after the December solstice (on average January 21). Diagnostic analysis reveals that the westward winds in the Southern (summer) Hemisphere were anomalously strong (maximum of ∼90 m/s) during December 2023, which significantly shortened the e‐folding time of QTDW‐W3, and additionally generated the QTDW‐W3 critical layers at the tropical summer stratopause from December 7. These two factors contributed to the earliest amplification of QTDW‐W3. In essence, the cold equatorial stratosphere triggered the exceptionally strong westward winds in the Southern Hemisphere via thermal wind balance, which was related to the enhanced upward middle‐atmosphere Hadley circulation during a prolonged Arctic stratopause warming event. Plain Language Summary As one of the prominent dynamic features in the Earth's summer middle and upper atmosphere, the quasi‐two‐day wave (QTDW) with westward zonal wavenumber 3 (W3) has significant influences on the global zonal‐mean circulation and temperature. Long‐term satellite and ground‐based observations have shown that the QTDW‐W3 is stably amplified twice yearly after the solstice, namely January/February in the Southern Hemisphere and July/August in the Northern Hemisphere. Such climatological features are very sensitive to the spatial distribution of the zonal‐mean zonal wind in the summer stratosphere and mesosphere. This study focuses on the unusual amplification of QTDW‐W3 just at the December solstice during the recent austral summer of 2023/2024, which has been never observed in the past 20 years of Aura Microwave Limb Sounder observations. Further analysis indicates that this earliest amplification of QTDW‐W3 was induced by a persistent and dramatic stratopause warming event in the Arctic (winter) stratosphere during December 2023, which caused the westward winds in the Southern (summer) Hemisphere to be anomalously strong via secondary Rossby wave‐induced interhemispheric coupling process. The current results first reveal that stratopause warming also has great potential to alter the global middle and upper atmospheric dynamics like the famous sudden stratospheric warming. Key Points The quasi‐two‐day wave (QTDW) with s=3$s=3$(W3) was maximized at the December solstice for the first time during the 2023/2024 austral summer The burst window for QTDW‐W3 appeared 2 weeks earlier than usual due to the anomalously strong summer westward winds in December 2023 The prolonged winter stratopause warming in December 2023 greatly enhanced the summer westward winds by cooling the equatorial stratosphere

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Atmosphere / Atmospheric circulation / Atmospheric dynamics / austral summer / Brittleness / Cerebral hemispheres / Hadley circulation / interhemispheric coupling / Lower mantle / Mesosphere / Northern Hemisphere / Planetary waves / quasi‐two‐day wave / Rossby waves / Satellite observation / Satellites / Solstices / Southern Hemisphere / Spatial distribution / Stratopause / stratopause warming / Stratosphere / Stratospheric warming / sudden stratospheric warming / Summer / Thermal winds / Upper atmosphere / Wavelengths / wave‐mean flow interaction / Winds / Winter / Zonal winds