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, diurnal, semidiurnal tidal amplitude and phases as well as the Reynolds stress components during 2019, utilizing meteor radars at six southern hemisphere locations ranging from from mid- 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 behaviour 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.

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

“…Liu et al, 2020;de Wit et al, 2017). The radar wind measurements also allow us to assess the impacts of the 2019 Antarctic SSW on the MLT dynamics during the SH winter (e.g., Stober et al, 2020).…”

Mesosphere and Lower Thermosphere Winds and Tidal Variations During the 2019 Antarctic Sudden Stratospheric Warming

“…Here this study extends such a direct comparison to include five radar stations across SH mid-to-high latitudes, and the study focuses on the day-to-day variations during a rare Antarctic Sudden Stratospheric Warming (SSW) in September 2019. Large disturbances in the MLT winds have been observed during this SSW (e.g., Liu, Janches, et al, 2021;Stober, Janches, et al, 2020). This study further assesses the NAVGEM-HA results and investigates the MLT tidal variations in response to the SH SSW.…”

“…Available observations are mostly obtained from ground-based medium frequency and meteor radars. These observations have continuous temporal sampling, but their spatial coverage is limited to only certain geographic locations (e.g., Stober, Janches, et al, 2020;Stober, Baumgarten, et al, 2020). Global winds have been simulated using general circulation models, but the modeled winds exhibit substantial discrepancies among different models (e.g., McCormack et al, 2021;Pedatella et al, 2014).…”

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

“…Atmospheric mean winds and tides are analyzed using the ASF, which is described in more detail in Baumgarten and Stober (2019) and Stober et al (2020a) and was already applied in several studies (Stober et al, 2017;Pokhotelov et al, 2018;Wilhelm et al, 2019;Stober et al, 2020b) to decompose MR winds in daily mean winds, diurnal and semidiurnal tides for the zonal and meridional components, respectively. The technique is implemented based on least square fits with full error propagation, which permits to apply the algorithm to unevenly sampled data with data gaps.…”

“…Furthermore, we minimize the impact of inertia-scale gravity waves on the tidal analysis by applying a vertical regularization to the tidal phases. In Stober et al (2020b) shows an example comparing the ASF2D with classical harmonic analysis for different window lengths. Due to the intermittent and non-stationary wave field generated by gravity waves and tides, long window lengths tend to produce artefacts and leak energy 7 https://doi.org/10.5194/acp-2021-142 Preprint.…”