01 Jul 2021

01 Jul 2021

Review status: this preprint is currently under review for the journal ACP.

Dynamical evolution of a minor sudden stratospheric warming in the Southern Hemisphere in 2019

Guangyu Liu1, Toshihiko Hirooka1, Nawo Eguchi2, and Kirstin Krüger3 Guangyu Liu et al.
  • 1Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
  • 2Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan
  • 3Department of Geosciences, University of Oslo, Oslo, Norway

Abstract. This study analyzes the Japanese 55-year Reanalysis (JRA-55) dataset from 2002 to 2019 to examine the sudden stratospheric warming event that occurred in the Southern Hemisphere (SH) in 2019 (hereafter referred to as SSW2019). Strong warming at the polar cap and decelerated westerly winds were observed, but since there was no reversal of westerly winds to easterly winds at 60° S in the middle to lower stratosphere, the SSW2019 is classified as a minor warming event.

The results show that quasi-stationary planetary waves of zonal wavenumber 1 developed during the SSW2019. The strong vertical component of the Eliassen–Palm flux with zonal wavenumber 1 is indicative of pronounced propagation of planetary waves to the stratosphere. The wave driving in September 2019 shows that the values are larger than those of the major SSW event in 2002 (hereafter referred to as SSW2002). Since there was no pronounced preconditioning (as in SSW2002) and the polar vortex was already strong before the SSW2019 occurred, a major disturbance of the polar vortex was unlikely to have taken place. The strong wave driving in SSW2019 occurred in high latitudes. Waveguides (i.e., positive values of the refractive index) are found at high latitudes in the upper stratosphere during the warming period, which provided favorable conditions for quasi-stationary planetary waves to propagate upward and poleward.

Guangyu Liu et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-444', Anonymous Referee #2, 12 Aug 2021 reply
    • EC1: '2nd review missed', Martin Dameris, 11 Oct 2021 reply

Guangyu Liu et al.

Guangyu Liu et al.


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Short summary
The Sudden Stratospheric Warming (SSW) event occurred September 2019 in the Southern Hemisphere was analyzed. A large warming and decelerated westerly winds were observed in the southern polar region. Since a reversal from westerly to easterly winds did not take place SSW2019 was classified as a minor SSW. The total wave forcing and the contribution from PW1 were larger in 2019.The strong and long-lasting planetary-scale wave with zonal wavenumber 1 played a role in the occurrence of SSW2019.