First Lidar Observations of Quasi‐Biennial Oscillation‐Induced Interannual Variations of Gravity Wave Potential Energy Density at McMurdo via a Modulation of the Antarctic Polar Vortex

Abstract

This work presents the first lidar observations of a Quasi‐Biennial Oscillation (QBO) in the interannual variations of stratospheric gravity wave potential energy density (Epm 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 Epm 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 Epm at McMurdo. The critical level filtering is characterized by wind rotation angle (WRA), and we find a linear correlation between the WRA and Epm interannual variations. The results suggest that the QBO is likely controlling the interannual variations of the Epm 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.

SABER Observations of Gravity Wave Responses to the Madden‐Julian Oscillation From the Stratosphere to the Lower Thermosphere in Tropics and Extratropics

“…According to the aforementioned studies, MJO P7 (P3) leads to a strengthened (weakened) polar vortex. This implies that strengthened (weakened) polar vortex corresponds to enhanced (suppressed) GWs, which is consistent with previous studies (Li et al, 2020; Triplett et al, 2018). Due to the lag of the MJO impacts on the polar vortex, the MJO impacts on GWs in the northern extratropics seem to be delayed accordingly.…”

“…The strong winds associated with PNJs are important sources of GWs in the winter hemisphere stratosphere (Fritts & Alexander, 2003; Sato & Yoshiki, 2008; Whiteway et al, 1997). In addition, less wind filtering in winter may also explain larger GW variances (Chu et al, 2018; Li et al, 2020; Zhao et al, 2017) than summer. Seasonal maximums are found in the tropics during the summer of each hemisphere (~20°N for JJA and ~20°S for DJF).…”

“…Thus when the polar vortex responds to the influence of MJO P3, the real‐time MJO is at P7 or P8. Due to this lag, MJO P7&8 (P3) correspond to a weakened (strengthened) polar vortex, which leads to suppressed (enhanced) GW activity (e.g., Li et al, 2020; Triplett et al, 2018). Notice that most of these previous studies focused on the NH.…”

Statistical analysis of the relationship between Quasi-Biennial Oscillation and Southern Annular Mode

“…Although the scope of this work was not to investigate the mechanisms of the QBO-SAM relationship, a possible cause of this link is wave propagation to the stratosphere, which affects the QBO and the polar stratospheric vortex (e.g., Baldwin and Tung, 1994;Thompson and Wallace, 2000;Fogt and Marshall, 2019;Li et al, 2020). The maximum of this wave propagation from the troposphere to the stratosphere in the SH occurs in late spring (Charney and Drazin, 1961;Randel and Newman, 1998).…”

“…Although it is a tropical phenomenon, the QBO influence on the extratropical regions has been investigated by several authors, mainly in HN (e.g., Tan, 1980, 1982;Baldwin and Tung, 1994;Coughlin and Tung, 2001;Naoe and Shibata, 2010;Kuroda and Yamazaki, 2010;Roy and Haigh, 2011;Anstey and Shepherd, 2014;Li et al, 2020). Holton and Tan (1980) showed that the geopotential height at high latitudes is significantly lower during the westerly QBO phase.…”