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Preprints
https://doi.org/10.5194/egusphere-2023-1044
https://doi.org/10.5194/egusphere-2023-1044
05 Jun 2023
 | 05 Jun 2023

Vortex Preconditioning of the 2021 Sudden Stratospheric Warming: Barotropic/Baroclinic Instability Associated with the Double Westerly Jets

Ji-Hee Yoo, Hye-Yeong Chun, and Min-Jee Kang

Abstract. This study explores the abrupt split of the polar vortex in the upper stratosphere prior to a recent sudden stratospheric warming event on 5 January 2021 (SSW21) and the mechanisms of vortex preconditioning by using the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA2) global reanalysis data. SSW21 is preceded by the highly distorted polar vortex that was initially displaced off the pole but eventually split at the onset date. Vortex splitting is most significant in the mid-stratosphere (1 hPa altitude) accompanied by the anomalous growth of westward-propagating planetary waves (PWs) of zonal wavenumber (ZWN) 2 (WPW2). While previous studies have suggested the East Asian trough as a potential source for the abnormal WPW2 growth, the prominent westward-propagating nature cannot be explained satisfactorily by the upward propagation of the quasi-stationary ZWN2 fluxes in the troposphere. More importantly, WPW2 exhibits an obvious in-situ excitation signature within the barotropically and baroclinically destabilized stratosphere, dominated by the easterlies descending from the stratopause containing the WPW2 critical levels. This suggests that the vortex split is attributed to the WPW2 generated in situ within the stratosphere via instability. Vortex destabilization is achieved as the double-jet structure consisting of a subtropical mesospheric core and a polar stratospheric core develops into SSW21 by encouraging the anomalous dissipation of the upward-propagating tropospheric ZWN1 PWs. This double-jet configuration is likely a favorable precursor for SSW onset, not only for the SSW21 but generally for most SSWs, through promoting the anomalous growth of unstable PWs as well as the enhancement of the tropospheric PW dissipation.

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Journal article(s) based on this preprint

05 Oct 2023
Vortex preconditioning of the 2021 sudden stratospheric warming: barotropic–baroclinic instability associated with the double westerly jets
Ji-Hee Yoo, Hye-Yeong Chun, and Min-Jee Kang
Atmos. Chem. Phys., 23, 10869–10881, https://doi.org/10.5194/acp-23-10869-2023,https://doi.org/10.5194/acp-23-10869-2023, 2023
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Short summary
The January 2021 Sudden stratospheric warming is preceded by the unusual double westerly jets...
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