We examine the characteristics of secondary gravity waves (GWs) excited by a localized (in space) and intermittent (in time) body force in the atmosphere. This force is a horizontal acceleration of the background flow created when primary GWs dissipate and deposit their momentum on spatial and temporal scales of the wave packet. A broad spectrum of secondary GWs is excited with horizontal scales much larger than that of the primary GW. The polarization relations cause the temperature spectrum of the secondary GWs generally to peak at larger intrinsic periods τ_Ir and horizontal wavelengths λ_H than the vertical velocity spectrum. We find that the one‐dimensional spectra (with regard to frequency or wave number) follow lognormal distributions. We show that secondary GWs can be identified by a horizontally displaced observer as “fishbone” or “>” structures in z − t plots whereby the positive and negative GW phase lines meet at the “knee,” z_knee, which is the altitude of the force center. We present two wintertime cases of lidar temperature measurements at McMurdo, Antarctica (166.69°E, 77.84°S) whereby fishbone structures are seen with z_knee=43 and 52 km. We determine the GW parameters and density‐weighted amplitudes for each. We show that these parameters are similar below and above z_knee. We verify that the GWs with upward (downward) phase progression are downward (upward) propagating via use of model background winds. We conclude that these GWs are likely secondary GWs having ground‐based periods τ_r=6–10 hr and vertical wavelengths λ_z=6–14 km, and that they likely propagate primarily southward.

Five years of atmospheric temperature data, collected with an Fe Boltzmann lidar by the University of Colorado group from 2011 to 2015 at Arrival Heights, are used to characterize the vertical wavelengths, periods, vertical phase speeds, frequency spectra, and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes. Over 1000 dominant gravity wave events are identified from the data. The seasonal spectral distributions of vertical wavelengths, periods, and vertical phase speeds in summer, winter, and spring/fall are found obeying a lognormal distribution. Both the downward and upward phase progression gravity waves are observed by the lidar, and the fractions of gravity waves with downward phase progression increase from summer ~59% to winter ~70%. The seasonal and monthly mean vertical wavelengths and periods exhibit clear seasonal cycles with vertical wavelength growing from summer ~5.5 km to winter ~8.5 km, and period increasing from summer ~4.5 h to winter ~6 h. Statistically significant linear correlations are found between the monthly mean vertical wavelengths/periods and the mean zonal wind velocities from 30 to 50 km. Assuming horizontal phase speeds independent of month, the monthly mean horizontal wavelengths, intrinsic periods, and group velocities are estimated for stratospheric gravity waves. The slopes of wave frequency spectra change from −1.9 at 30–60 km to −1.45 around 60–65 km. The vertical wave number spectra show the power spectral density at vertical wavelengths of 5–20 km decreasing from winter maximum to summer minimum. Several aforementioned features are observed for the first time in Antarctica.

Five years of Fe Boltzmann lidar's Rayleigh temperature data from 2011 to 2015 at McMurdo are used to characterize gravity wave potential energy mass density (E_pm), potential energy volume density (E_pv), vertical wave number spectra, and static stability N² in the stratosphere 30–50 km. E_pm (E_pv) profiles increase (decrease) with altitude, and the scale heights of E_pv indicate stronger wave dissipation in winter than in summer. Altitude mean and obey lognormal distributions and possess narrowly clustered small values in summer but widely spread large values in winter. and vary significantly from observation to observation but exhibit repeated seasonal patterns with summer minima and winter maxima. The winter maxima in 2012 and 2015 are higher than in other years, indicating interannual variations. Altitude mean varies by ~30–40% from the midwinter maxima to minima around October and exhibits a nearly bimodal distribution. Monthly mean vertical wave number power spectral density for vertical wavelengths of 5–20 km increases from summer to winter. Using Modern Era Retrospective Analysis for Research and Applications version 2 data, we find that large values of during wintertime occur when McMurdo is well inside the polar vortex. Monthly mean are anticorrelated with wind rotation angles but positively correlated with wind speeds at 3 and 30 km. Corresponding correlation coefficients are −0.62, +0.87, and +0.80, respectively. Results indicate that the summer‐winter asymmetry of is mainly caused by critical level filtering that dissipates most gravity waves in summer. variations in winter are mainly due to variations of gravity wave generation in the troposphere and stratosphere and Doppler shifting by the mean stratospheric winds.

This work presents the first lidar observations of a Quasi‐Biennial Oscillation (QBO) in the interannual variations of stratospheric gravity wave potential energy density (E_pm in 30–50 km) at McMurdo (77.84°S, 166.67°E), Antarctica. This paper also reports the first identification of QBO signals in the distance between McMurdo and the polar vortex edge. Midwinter stratospheric gravity wave activity is stronger during the QBO easterly phase when the June polar vortex expands and the polar night jet shifts equatorward. During the QBO westerly phase, gravity wave activity is weaker when the polar vortex contracts and the polar night jet moves poleward. Nine years of lidar data (2011–2019) exhibit the mean E_pm winter maxima being ~43% higher during QBO easterly than westerly. The June polar vortex edge at 45 km altitude moves equatorward/poleward during QBO easterly/westerly phases with ~8° latitude differences (39.7°S vs. 47.7°S) as revealed in 21 years of MERRA‐2 data (1999–2019). We hypothesize that an equatorward shifted polar vortex corresponds to less critical level filtering of gravity waves and thus higher E_pm at McMurdo. The critical level filtering is characterized by wind rotation angle (WRA), and we find a linear correlation between the WRA and E_pm interannual variations. The results suggest that the QBO is likely controlling the interannual variations of the E_pm winter maxima over McMurdo via the critical level filtering. This observationally based study lays the groundwork for a rigorous numerical study that will provide robust statistics to better understand the mechanisms that link the tropical QBO to extratropical waves.