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Roles of Gravity Waves in Preconditioning of a Stratospheric Sudden Warming       
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  • Haruka Okui,
  • Dai Koshin,
  • Shingo Watanabe,
  • Kaoru Sato
Haruka Okui
The University of Tokyo

Corresponding Author:[email protected]

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Dai Koshin
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Shingo Watanabe
Japan Agency for Marine-Earth Science and Technology
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Kaoru Sato
The University of Tokyo
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As well as strong upward propagation of planetary waves from the troposphere, the state of the stratospheric mean flow has been recognized as a key factor for the occurrence of stratospheric sudden warmings (SSWs). The modification of the mean flow to a suitable state for an SSW occurrence is called “vortex preconditioning”. Recently, increasing attention has been paid to the role of gravity waves (GWs) in the preconditioning mechanism. However, because of the limited availability of datasets covering the whole neutral atmosphere, much uncertainty still exists in the role of GWs in the preconditioning. The aim of this study is to investigate the mechanism of modification of the mean flow in the stratosphere and mesosphere before SSWs from a climatological viewpoint and elucidate the role of GWs in it. We use two state-of-the-art datasets covering the whole neutral atmosphere: a 17-year medium-resolution reanalysis dataset and the output data from hindcast simulations performed with a GW-permitting general circulation model. It is shown that the second principal component of the zonal-mean zonal wind in the stratosphere and mesosphere tends to show a maximum prior to an SSW, characterizing preconditioning. GW forcing alters the structure of the upper part of the jet and contributes to the preconditioning along with planetary waves. Comparison of GW forcing between the reanalysis and GW-permitting model suggests that the magnitude of parameterized GW forcing is approximately half that of the GW forcing in the polar upper stratosphere where the forcing is responsible for the preconditioning.
07 May 2024Submitted to ESS Open Archive
10 May 2024Published in ESS Open Archive