Structure, Variability, and Mean‐Flow Interactions of the January 2015 Quasi‐2‐Day Wave at Middle and High Southern Latitudes

Abstract

The structure, variability, and mean‐flow interactions of the quasi‐2‐day wave (Q2DW) in the mesosphere and lower thermosphere during January 2015 were studied employing meteor and medium‐frequency radar winds at eight sites from 23°S to 76°S and Microwave Limb Sounder (MLS) temperature and geopotential height measurements from 30°S to 80°S. The event had a duration of ~20–25 days, dominant periods of ~44–52 hr, temperature amplitudes as large as ~16 K, and zonal and meridional wind amplitudes as high as ~40 and 80 m/s, respectively, at middle and lower latitudes. MLS measurements enabled definition of balance winds that agreed well with radar wind amplitudes and phases at middle latitudes where amplitudes were large and quantification of the various Q2DW modes contributing to the full wave field. The Q2DW event was composed primarily of the westward zonal wavenumber 3 (W3) mode but also had measurable amplitudes in other westward modes W1, W2, and W4; eastward modes E1 and E2; and stationary mode S0. Of the secondary modes, W1, W2, and E2 had the larger amplitudes. Inferred MLS balance winds enabled estimates of the Eliassen‐Palm fluxes for each mode, and cumulative zonal accelerations that were found to be in reasonable agreement with radar estimates from ~35°S to 70°S at the lower altitudes at which radar winds were available.

Wavenumbers 3 and 4 Quasi 2‐day Wave Activities Observed by Multiple Meteor Radars in the Two Hemispheres During Austral Summer

“…Similar latitudinal structures of the W3 in the zonal wind, meridional wind and temperature at mid latitudes of the SH are reported by Fritts et al. (2019). As shown in Figure 6, there are the two amplitude peaks in the zonal wind, we examine the phase relation between the two regions with strong wave activities.…”

“…In all the zonal and meridional winds and temperature, the zonal wavenumber is −3 in the first QTDW event, but −4 in the second one, and there are no other strong QTDW modes during the 60‐day duration, such as W2. In different SH summers, other modes, such as W2, E1, E2, and E3, may exhibit significant activities (Fritts et al., 2019; Harris & Vincent, 1993; He, Chau, et al., 2021; He, Forbes, et al., 2021), which implies that the QTDW bursts are the generality in the SH summer but the modes might slightly change from summer to summer. The spectral peaks of 25.3 ms −1 , 19.8 ms −1 , and 8.4 K of the W3 in the meridional wind, zonal wind and temperature are larger than those of 17.4 ms −1 , 11.7 ms −1 , and 5.5 K of the W4, which is consistent with the results in Figures 2 and 3.…”

“…In order to investigate the global structure of the W3 and W4 components, we extract the amplitudes of the W3 and W4 modes in the zonal and meridional winds and temperature from the reanalysis data by using a two‐dimensional least squares fit. Considering that the W2 component arises frequently in the MLT (Fritts et al., 2019), the W2 mode is also fitted together. The fitting expression is written as $$$f(\theta ,\,t)={{f}_{0}}_{j}+\sum\limits _{j=1}^{3}{A}_{j}\,\sin \left(\frac{2\pi }{T}t-{k}_{j}\theta -{{\Phi}}_{j}\right)$$$ where the subscript $$j$$ = 1, 2 and 3 denotes the W2, W3, and W4 modes; $$\theta $$ is the longitude in units of radian; $$t$$ is the time; $$f$$ represents the fitted quantity, that is, the zonal wind, meridional wind and temperature, respectively; $${f}_{0}$$ denotes the mean value of the fitted quantity; $$A$$ and $${\Phi}$$ are the amplitudes and initial phase, respectively; $$T$$ = 46 hr is the period of the QTDW; and $$k$$ = −2, −3 and −4 denote the zonal wavenumber of the W2, W3, and W4, respectively.…”

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

“…The MLT winds have been measured near 60°S latitude by three meteor radars at Rio Grande, Tierra del Fuego (TDF; 53.7°S, 67.7°W) in Southern Argentina, King Edward Point station (KEP; 54.3°S, 36.5°W) on South Georgia Island, and King Sejong Station (KSS; 62.2°S, 58.8°W) on King George Island on the Northern tip of the Antarctic Peninsula. These meteor radar winds allow us to identify the wave activities and large‐scale variations in the MLT region in this key dynamic but largely unexplored area (e.g., Eswaraiah et al., 2016; Fritts et al., 2019; Iimura et al., 2015; Lee et al., 2013; G. 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

“…The mesosphere and lower thermosphere (MLT) exhibit dramatic variations during austral winter near 60° latitude in the Southern Hemisphere (SH), covering the Southern Andes, the Drake Passage, and the Antarctic Peninsula area (e.g., Alexander et al., 2008; de Wit et al., 2017; Dowdy et al., 2004; Fritts et al., 2019; Liu, Janches, et al., 2021; Stober, Baumgarten, et al., 2020; Stober, Janches, et al., 2020). These variations account for both large‐ and small‐scale motions including tides and gravity waves.…”