Gravity Wave Activities in the Upper Mesosphere Observed at King Sejong Station, Antarctica (62.22°S, 58.78°W) and Their Potential Sources in the Lower Atmosphere

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; 62.22S, 58.78W) for 8 years (20072014). GW activities are estimated through hourly GW wind variances obtained from an improved methodology that explicitly removes large-scale wind components (including tides and planetary waves such as 2- and 4-day waves) from observed meteor echoes. A clear semi-annual variation of the GW activities with solstitial maxima and equinoctial minima exists, except above 94 km where GW activities are strong in AugustSeptember. Potential GW sources in the lower atmosphere, including orography, jet stream, and deep convection, are investigated using reanalysis datasets. Orography around KSS is a likely source of 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), significantly correlate 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 at midlatitudes is a likely source of the GWs in nearly all seasons, with the strongest correlation in storm tracks in winter.