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An unusual sudden stratospheric warming (SSW) event occurred in the Southern Hemisphere in September 2019. Ground-based and satellite observations show the presence of transient eastward- and westward-propagating quasi-10 day planetary waves (Q10DWs) during the SSW. The planetary wave activity maximizes in the mesosphere and lower thermosphere region approximately 10 days after the SSW onset. Analysis indicates that the westward-propagating Q10DW with zonal wave number s = 1 is mainly symmetric about the equator, which is contrary to theory which predicts the presence of an antisymmetric normal mode for such planetary wave. Observations from microwave limb sounder and sounding of the atmosphere using broadband emission radiometry are combined with meteor radar wind measurements from Antarctica, providing a comprehensive view of Q10DW wave activity in the Southern Hemisphere during this SSW. Analysis suggests that the Q10DWs of various wavenumbers are potentially excited from nonlinear wave-wave interactions that also involve stationary planetary waves with s = 1 and s = 2. The Q10DWs are also found to couple the ionosphere with the neutral atmosphere. The timing of the quasi-10-day oscillations (Q10DOs) in the ionosphere are contemporaneous with the Q10DWs in the neutral atmosphere during a period of relatively low solar and geomagnetic activity, suggesting that the Q10DWs play a key role in driving the ionospheric Q10DOs during the Southern SSW event. This study provides observational evidence for coupling between the neutral atmosphere and ionosphere through the upward propagation of global scale planetary waves. [ABSTRACT FROM AUTHOR]

A sudden stratospheric warming (SSW) is an extremely rare event in the Southern Hemisphere (SH), but occurred in early September 2019. From the Antarctic meteor radar (MR) stations, Davis (68.6°S, 77.9°E) and King Sejong Station (62.2°S, 58.8°W), quasi 10-day oscillations were clearly observed in the zonal mesospheric winds before the central date (DOY 253) of the SSW. From the northern low-latitude Tirupati (13.6°N, 79.4°E) MR, a strong wave activity with a period of ~6 days was detected in the zonal winds right after the central date. This oscillation is also seen in the geopotential height measurements from the Microwave Limb Sounder (MLS) on board the Aura satellite near the Tirupati region. To elucidate the possible source of the quasi 6-day wave (Q6DW), we use a specified dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM) constrained by the reanalysis data from the surface to 50 km. The simulation results show that the amplitude of the westward and equatorward propagating Q6DW was enhanced after the SSW central date in the MLT region, and the Q6DW can be attributed to the baroclinic/barotropic instability in the SH high-latitude mesosphere where the divergence of Eliassen-Palm flux occurred. Thus, we suggest that the Q6DW activity observed by the Tirupati MR and MLS originated from the SH high-latitude mesospheric region. Both the observation and the simulation results clearly demonstrate that the 2019 SH SSW affected not only the high-latitude MLT region but also the low-latitude MLT region. [ABSTRACT FROM AUTHOR]

The strongest Southern Hemisphere minor sudden stratospheric warming (SSW) in the last 40 years occurred in September 2019 and resulted in unprecedented weakening of the stratospheric polar vortex. Ionospheric total electron content (TEC) observations are used to provide an overview of statistically significant anomalies in the low‐latitude ionosphere during this event. Quasi‐semidiurnal perturbations of TEC are observed in response to the SSW, similar to those seen during Northern Hemisphere SSWs. Analysis indicates the existence of quasi‐periodic oscillations in TEC in the crests of the equatorial ionization anomaly, with strong 5‐ to 6‐day and 2‐ to 3‐day periodicities. Ionospheric anomalies from the combined effects of multiple mechanisms exceed a factor of 2, comparable to the strongest anomalies associated with Northern Hemisphere SSWs. These results also indicate a remarkable longitudinal variation in the character and magnitude of variations that could be related to a modulation of the non‐migrating diurnal tide. Plain Language Summary: Sudden stratospheric warming, a large‐scale meteorological disturbance, has been associated with profound anomalies in the Earth atmosphere, from troposphere all the way to the upper thermosphere and ionosphere. During the last decade, numerous studies showed that Arctic sudden stratospheric warmings cause especially large anomalies in the low‐latitude ionosphere. However, it was not clear if similar ionospheric anomalies can be produced by Antarctic sudden stratospheric warming, mostly because Antarctic sudden stratospheric warmings are pretty rare. In this study, we provide an overview of ionospheric anomalies in total electron content observed in September 2019, when very strong sudden stratospheric warming developed over Antarctica. We conclude that Antarctic events produce even more dynamical changes in the ionosphere than Arctic events. We report for the first time large differences in the observed features at locations that are separated by only 30° in longitude. Our results indicate that stratospheric weather can strongly influence the state of the ionosphere not only during December–February period (winter in the Northern Hemisphere), but also during September (equinox conditions). Key Points: Minor Antarctic sudden stratospheric warming of September 2019 produces large ionospheric anomalies at low latitudesChanges of total electron content exceeding a factor of 2 are observedLarge longitudinal differences in total electron content response to Antarctic SSW are reported [ABSTRACT FROM AUTHOR]