Gravity Wave Activities in the Upper Mesosphere Observed by Meteor Radar at King Sejong Station, Antarctica and Their Potential Sources

Abstract

Gravity wave (GW) activities in the upper mesosphere and their potential sources in the lower atmosphere are investigated using meteor radar observations at King Sejong Station, Antarctica (KSS; 62.22°S, 58.78°W) during 2007-2014. GW activities are estimated through hourly wind variances obtained from an improved methodology that explicitly removes large-scale wind components (including planetary waves and tides) from observed meteor echoes. A semi-annual variation of the GW activities with solstitial maxima and equinoctial minima is evident, except above 94 km where GW activities are strong in August-September. Potential GW sources in the lower atmosphere, including orography, jet stream, and deep convection, are investigated. Steep orography around KSS is a likely source of the GWs in winter and autumn, as stationary mountain waves can propagate up into the upper mesosphere without being filtered by the westerlies from the surface to the upper mesosphere. The residual of the nonlinear balance equation at 5 hPa, which is a diagnostic of flow imbalance associated with the polar night jet (PNJ), correlate well with the observed GW activities at z = 98 km during spring and autumn, while no significant correlation is found in wintertime due to critical-level filtering and Doppler shifting via the strong PNJ. Deep convection over mid-latitudes is a likely source of the observed GWs in nearly all seasons, with significant correlations in storm tracks in winter.