Possible Causes of the Occurrence of a Rare Antarctic Sudden Stratospheric Warming in 2019

Xin Tan,Ming Bao,Chenming Ma,Pengkun Yang

doi:10.3390/atmos13010147

Xin Tan, Ming Bao + Show 2 more

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https://doi.org/10.3390/atmos13010147

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Journal: Atmosphere	Publication Date: Jan 17, 2022
Citations: 1	License type: CC BY 4.0

Affiliation: China University of Geosciences, Nanjing University

Abstract

A minor Antarctic sudden stratospheric warming (SSW) with the strongest circulation changes since the first major SSW over the Antarctic was recorded in 2002 occurred in early September 2019. The diagnosis demonstrates two possible causes of this SSW. First, the tropical central Pacific warming is identified, which enhanced the amplitude of tropospheric planetary wavenumber 1 (W1) in the extratropics on the seasonal time scale. Second, the impact of intraseasonal convection anomalies similar to previous studies is also suggested here. The enhanced deep convection over the South Pacific Convergence Zone (SPCZ) in late August–early September excited a Rossby wave train to deepen an anomalous ridge, which significantly and persistently strengthened the tropospheric W1. The central Pacific warming and intraseasonal convection anomalies jointly provided the conditions for the occurrence of the Antarctic SSW in 2019 on different time scales. On the other hand, the difference of the stratospheric state between the Antarctic SSWs in 2019 and 2002 may be an important reason why the 2019 event did not meet the major SSW criteria. The stratospheric state before the 2019 SSW event is somewhat not as ideal as that of the 2002 event. Vertical planetary waves are, hence, more difficult to enter into the polar stratosphere, making it more difficult to trigger major events.

Highlights

Since the first recorded major sudden stratospheric warming (SSW) occurred over Antarctica in 2002 [1,2,3,4], a large amplitude of polar vortex disturbance has been absent for a long time in the Southern Hemisphere
It was suggested that the circulation anomalies associated with Antarctic SSW can descend from the stratosphere to the troposphere, and the relevant Southern Annular Mode (SAM) anomaly can even persist for up to about 90 days [10]
During July-August-September (JAS) in 2019, the first warming of 10 hPa temperature over the polar cap occurred in late August, rising by about 20 K (Figure 1a)

Summary

Introduction

Since the first recorded major sudden stratospheric warming (SSW) occurred over Antarctica in 2002 [1,2,3,4], a large amplitude of polar vortex disturbance (close to the major SSW) has been absent for a long time in the Southern Hemisphere. Many works have suggested that anomalous tropospheric planetary waves propagating into the stratosphere could contribute to the weakening of the polar vortex, especially SSW [5,6,7]. Atmosphere 2022, 13, 147 propagation of planetary waves into the stratosphere and lead to Antarctic SSWs [13,17].

Results

Conclusion