Characteristics of Gravity Wave Horizontal Phase Velocity Spectra in the Mesosphere Over the Antarctic Stations, Syowa and Davis.

Mesospheric gravity‐wave (GW) phase velocity spectra and total powers at two Antarctic stations, Davis and Syowa, were derived using OH airglow data from March to October in 2016. The total powers have similar seasonal variation, that is, maxima in winter at both stations. The average powers at both stations in winter were not significantly different. However, the power at Davis in September was three times smaller than that at Syowa. This lower power at Davis was attributed to GWs with omnidirectional phase velocity. These lower GW activities at Davis could be attributed to a longitudinal variation in wave filtering; a stronger wind at Davis filtered out more GWs than at Syowa. Also, to explore possible sources in the middle atmosphere, we investigated one event, in which GWs with ∼100 ms−1 southeastward phase velocity appeared at Davis on 29 August. The raytracing method was applied, and its result indicated that those GWs with high southeastward phase velocity propagated from ∼45 km altitude or higher over the Southern Ocean. A large residual of the non‐linear balanced equation was found at 50 km on its ray path. GWs, very likely emitted from a tropospheric jet, were also found near the ray path at the termination altitude over the Southern Ocean and possibly appeared saturated between 45 and 50 km. Therefore, the OH imager at Davis probably captured GWs generated by a spontaneous adjustment in the upper stratosphere and/or secondary GWs produced by the breaking of the GWs that have originated from the tropospheric jet. Plain Language Summary: A gravity wave (GW) is a type of atmospheric wave that transports momentum from the Earth's surface to the edge of the atmosphere where it can drive atmospheric circulations. The temporal and spatial variation of GWs is not well understood, and their sources remain unclear. We observed GWs at the upper edge of the atmosphere over two Antarctic stations (Syowa and Davis) and calculated their phase velocity and total power spectra. The total powers have winter maxima at both stations. Although the average powers at both stations in winter were not significantly different, the power at Davis in September was three times smaller than that at Syowa. The lower GW activity at Davis could be attributed to a stronger wind at Davis, which filtered out more GWs than at Syowa. Also, to explore possible sources in the middle atmosphere, we investigated one event at Davis on 29 August 2016. We found that some GWs propagated from ∼45 km altitude or higher over the Southern Ocean. Those GWs could be emitted from the polar night jet (flow imbalance) and/or secondary GWs produced by the breaking of the GWs that have originated from the tropospheric jet. Key Points: Mesospheric gravity‐wave activity at two Antarctic stations was larger in winter than in spring and fallWave activity at Davis was not significantly different with Syowa in winter but smaller in fall, which can be explained by filtering effectWe find that GWs at Davis on 29 August 2016, were very likely generated by a spontaneous adjustment and/or a tropospheric jet wave breaking [ABSTRACT FROM AUTHOR]