Seasonal evolution of winds, atmospheric tides, and Reynolds stress components in the Southern Hemisphere mesosphere–lower thermosphere in 2019

Abstract

Abstract. In this study we explore the seasonal variability of the mean winds and diurnal and semidiurnal tidal amplitude and phases, as well as the Reynolds stress components during 2019, utilizing meteor radars at six Southern Hemisphere locations ranging from midlatitudes to polar latitudes. These include Tierra del Fuego, King Edward Point on South Georgia island, King Sejong Station, Rothera, Davis, and McMurdo stations. The year 2019 was exceptional in the Southern Hemisphere, due to the occurrence of a rare minor stratospheric warming in September. Our results show a substantial longitudinal and latitudinal seasonal variability of mean winds and tides, pointing towards a wobbling and asymmetric polar vortex. Furthermore, the derived momentum fluxes and wind variances, utilizing a recently developed algorithm, reveal a characteristic seasonal pattern at each location included in this study. The longitudinal and latitudinal variability of vertical flux of zonal and meridional momentum is discussed in the context of polar vortex asymmetry, spatial and temporal variability, and the longitude and latitude dependence of the vertical propagation conditions of gravity waves. The horizontal momentum fluxes exhibit a rather consistent seasonal structure between the stations, while the wind variances indicate a clear seasonal behavior and altitude dependence, showing the largest values at higher altitudes during the hemispheric winter and two variance minima during the equinoxes. Also the hemispheric summer mesopause and the zonal wind reversal can be identified in the wind variances.

Interhemispheric differences of mesosphere–lower thermosphere winds and tides investigated from three whole-atmosphere models and meteor radar observations

“…The first observational evidence was obtained at McMurdo through an investigation of lidar observations . More recently a detailed study of the MLT dynamics for the year 2019 using six meteor radars from Tierra del Fuego, South Georgia, Rothera, King Sejong Station, Davis, and McMurdo indicated a strong impact of non-primary waves above the Andes and Antarctic Peninsula on the daily mean zonal and meridional winds and momentum fluxes (Stober et al, 2021b). Including nonprimary waves in the GW parameterizations for the hemispheric winter could add eastward momentum to the MLT, which is apparently too weak in WACCM-X(SD) and UA-ICON.…”

Wind Variations in the Mesosphere and Lower Thermosphere Near 60°S Latitude During the 2019 Antarctic Sudden Stratospheric Warming

“…Ground‐based observations can be continuous in time, but they have limited coverages to certain locations. Observations of SH midlatitudes to high latitudes are thus relatively sparse, and this region remains largely unexplored (e.g., Stober et al., 2020).…”

“…The 2002 event is the only major SSW that has ever been observed at high‐southern latitudes (e.g., Krüger et al., 2005). Minor warming events have occurred recently in the SH during the 2010 and 2019 Antarctic winter (e.g., Eswaraiah et al., 2016; Stober et al., 2020).…”

“…These mostly include the 2002 major warming and the 2010 minor warming events, and multi‐day oscillations with periods ∼14–16 days were observed in the MLT region during both events (e.g., Dowdy et al., 2004; Eswaraiah et al., 2016, 2018). Most recently, an unusual SSW driven by exceptionally strong planetary wave activity occurred in the SH during September 2019 (e.g., Stober et al., 2020; Yamazaki et al., 2020). Although this SSW is categorized as a minor warming event, it features a very large temperature increase of ∼50 K at ∼30 km altitude over the South pole.…”

Interhemispheric differences of mesosphere/lower thermosphere winds and tides investigated from three whole atmosphere models and meteor radar observations

“…A first observational evidence was obtained at McMurdo investigating lidar observations . More recently a detailed study of the MLT dynamics for the year 2019 using six meteor radars from Tierra del Fuego, South Georgia, Rothera, King Sejong Station, Davis and McMurdo indicated a strong impact of non-primary waves above the Andes and Antarctic Peninsula on the daily mean zonal and meridional winds and momentum fluxes (Stober et al, 2021). Including non-primary waves into the GW parameterizations for the hemispheric winter could add eastward momentum to the MLT, which is apparently too weak in WACCM-X(SD) and UA-ICON.…”