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

Abstract

AbstractMesospheric 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.