Roles of Gravity Waves in Preconditioning of a Stratospheric Sudden Warming

H. Okui, D. Koshin, S. Watanabe, K. Sato

Research output: Contribution to journalArticlepeer-review

Abstract

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 data sets 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 data sets covering the whole neutral atmosphere: a 17-year medium-resolution reanalysis data set 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.

Original languageEnglish
Article numbere2023JD039881
JournalJournal of Geophysical Research: Atmospheres
Volume129
Issue number10
Early online date23 May 2024
DOIs
Publication statusPublished - 28 May 2024
Externally publishedYes

Data Availability Statement

The processed data from the JAGUAR-DAS reanalysis data set and JAGUAR hindcast outputs are available from https://pansy.eps.s.u-tokyo.ac.jp/archive_data/Okui_etal_preconditioning/. Figures were produced using the GFD DENNOU Library (https://www.gfd-dennou.org/arch/dcl/dcl-7.5.1/).

Keywords

  • atmospheric reanalysis
  • general circulation model
  • gravity waves
  • middle atmosphere
  • planetary waves
  • stratospheric sudden warming

ASJC Scopus subject areas

  • Geophysics
  • Atmospheric Science
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)

Cite this