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
image data from March to October in 2016. The total powers have similar
seasonal variation, that is, maxima in winter at both stations. However,
the power at Davis was one standard deviation larger in winter and three
times smaller in September than at Syowa. The total power at Davis in
winter was mainly attributed to GWs with high eastward ( phase velocity.
On the other hand, the higher total power at Syowa in September was
attributed to GWs with omnidirectional phase velocity. These differences
between Syowa and Davis can not be explained by the wind filtering
effect, and other factors are needed. To further explorer the origin of
the difference in winter, we focused on an event on August 29, 2016, in
which GWs with ~100 ms-1 southeastward
phase velocity appeared at Davis. The raytracing method was applied, and
its result indicated that those GWs with high southeastward phase
velocity propagated from ~45 km altitude over the
southern ocean (~ where GWs with high amplitude and
southeastward propagating emitted from the tropospheric jet appeared.
These jet GWs were probably saturated in 45-50 km altitudes. Therefore,
the GWs with eastward phase velocity were probably secondary gravity
waves. This result suggests that the higher power in the eastward high
phase velocity domain at Davis was contributed to by secondary GWs.