Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

Michal Kozubek,Jan Lastovicka,Peter Krizan

doi:10.3390/atmos11101063

Abstract

An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.

Highlights

Sudden stratospheric warmings (SSWs) are one of the most impressive dynamical events in the stratosphere
We present results for both pressure levels (1 and 10 hPa), where we can expect a strong effect of stratospheric warming
The bottom panels show us zonal wind at 60◦ N or S, which is important for classification of SSWs

Summary

Introduction

Sudden stratospheric warmings (SSWs) are one of the most impressive dynamical events in the stratosphere These events include a large and rapid temperature increase (>30–40 K on time-scale of days) in the mid- to upper stratosphere (30–50 km) and, in the cases called major, a reversal of the climatological westerly zonal-mean zonal winds associated with the stratospheric polar night jet (e.g., [1,2,3]). They are usually driven by the breaking of planetary waves from the troposphere in the stratosphere. Important point of major SSW event definition is a duration of easterly zonal-mean zonal winds because the zonal mean zonal wind reversal could be short (about 1 day) and very weak (with values only slightly below zero)

Results

Discussion

Conclusion