Record‐Strong Eastward Propagating 4‐Day Wave in the Southern Hemisphere Observed During the 2019 Antarctic Sudden Stratospheric Warming

Based on the zonal winds from the Modern‐Era Retrospective Analysis for Research and Applications, version 2 reanalysis data, we investigate the enhancement of an eastward propagating 4‐day wave (E4DW) during the 2019 Antarctic sudden stratospheric warming (SSW). The amplitudes of E4DW are centered at 50°S and 50 km with a maximum amplitude of ∼20 m/s. The enhanced E4DW significantly exceeds the climatological level and has the strongest amplitude in the Southern Hemisphere since 1980. Our results show that the E4DW is generated by the atmospheric instabilities via a double‐jet configuration of the zonal mean zonal winds. Our analysis further indicates that the special structure of the zonal mean zonal winds caused by the 2019 Antarctic SSW at the stratopause is responsible for the excitation of the record‐strong E4DW in 2019 in the Southern Hemisphere. Plain Language Summary An extraordinary Antarctic sudden stratospheric warming (SSW) occurred in September 2019. Responses of westward propagating quasi‐6‐day and quasi‐10‐day planetary waves to the 2019 Antarctic SSW have been widely reported in recent studies. However, the enhancement of an eastward propagating 4‐day wave (E4DW) is also observed during this SSW. The amplitude of the E4DW is significantly larger than the climatological level and is the strongest in the Southern Hemisphere since 1980. We further explore the trigger mechanism of the record‐strong E4DW that occurred during the 2019 Antarctic SSW for the first time. The special configuration of zonal mean zonal winds with the abnormal instabilities at the stratopause during the 2019 Antarctic SSW is the main reason for the enhancement of E4DW. Our results could help in understanding the activity of eastward propagating planetary waves in the middle atmosphere during SSWs. Key Points The eastward propagating 4‐day wave (E4DW) in September 2019 has the strongest amplitude in the Southern Hemisphere since 1980 The exceptional E4DW is triggered by atmospheric instabilities under a double‐jet configuration of the zonal mean zonal winds The 2019 Antarctic sudden stratospheric warming results in a special vertical wind shear at the stratopause for the generation of E4DW