Southern Hemisphere Stratospheric Warmings and Coupling to the Mesosphere‐Lower Thermosphere

Abstract

Twenty six years of medium frequency (MF) radar wind measurements made from 1994 to 2019 at Davis Station (68.6°S, 77.9°E) are used to study the mean response of the mesosphere‐lower thermosphere to stratospheric warmings in the Southern Hemisphere. Warming events were detected using Modern‐Era Retrospective Analysis for Research and Applications (MERRA2) data with a systematic search for reductions in the zonal‐mean circulation at 60°S and corresponding increases in polar temperatures. Some 37 events were identified, including the 2002 major warming and the large event of 2019, with an average of 1–2 warmings per year. At the 10 hPa level, the polar cap temperature increases ranged from 3 to 28 K, with a mean value of 12 K, while the zonal wind speed reductions varied between −6 and −43 ms−1, with a mean value of −15 ms−1. Peak values occurred near 40 km. Warmings occurred mainly between August and October, with a small peak in occurrence in April/May. The MF radar data showed an average reduction in the mesospheric eastward winds of about 5–7 ms−1 at heights near 75 km that occurred 3–4 days prior to the changes in the stratosphere. Warming events were driven by episodic intensifications in planetary wave amplitudes, with quasi‐stationary planetary scale waves (PW) 1 being especially important. PW Eliassen‐Palm flux divergences show a systematic behavior with time and height that is consistent with a poleward residual circulation and downwelling over the pole prior to the warming events and an equatorward flow and upwelling after the peak of the events.

Prolonged Quasi‐6‐Day Wave Activities in the Northern Hemisphere MLT Region Due To Antarctic Stratospheric Minor Warming Around September Equinox of 2013 and 2014

“…Our identification of Antarctic SMW events in 2013 and 2014 is the same as the results of Vincent et al. (2022).…”

“…Meanwhile, the stratospheric polar vortex in the SH was distorted during SMWs, but it remained at a high strength over most areas of the polar region. Our identification of Antarctic SMW events in 2013 and 2014 is the same as the results of Vincent et al (2022).…”

“…This is consistent with the fact that the shape of the Antarctic polar vortex was dominated by an obvious wavenumber 1 structure during Antarctic SMW events in September 2013 and 2014 (Figure 5e-5j). Multiyear composite results in Vincent et al (2022) confirm that SPW1 plays a dominant role in the generation of Antarctic SSW events. Figure 6e-6h display the temporal and altitudinal variations in the atmospheric residual circulation (v * = v ρv′θ′ /θ z ) z /ρ and w * = w + cos ϕv′θ′ / θ z ) ϕ / (a cos ϕ) ) at 60°-90°S during day 230-300 in 2013 and 2014.…”

“…Although major SSW events are rare in the Antarctic region, stratospheric minor warming (SMW) events are more frequent in the SH during wintertime (Alajmi et al., 1985; Coy et al., 2005; Hirota et al., 1990; Laat & Weele, 2011; Shiotani et al., 1993; Vincent et al., 2022), which may also lead to large‐scale anomalies in the background atmosphere to influence traveling PW activities in the MLT region. In this paper, the specific criteria for the Antarctic SMW events are as follows (Vincent et al., 2022): (a) Warmings at 60°–90°S and 10 hPa and increase in the meridional temperature gradient ([$$\overline{T}$$ (80°–90°S)‐$$\overline{T}$$ (60°–70°S)]/20°) at 10 hPa; (b) The deceleration in the zonal mean zonal wind at 60°S at any level from 10 hPa to 0.01 hPa (the wind reversal is not required). In addition, changes in the morphology of the polar vortex and residual circulation can be regarded as additional evidence for the occurrence of SMW.…”

Dual-Frequency, Dual-Mode Reconfigurable Digital Atmospheric Radar Receiver Design

“…Atmospheric radio radars, such as medium frequency radars [1,2], meteor radars [3], and MST radars [4], play a significant role in the study of the dynamics and coupling of middle atmosphere and ground weather. They contribute to understanding the physics of atmospheric motion and sudden weather processes, establishing high-precision and high-resolution atmospheric models [5][6][7]. The atmospheric radio radar began to develop towards the trend of multifunctional comprehensive integration.…”