FURTHER OBSERVATIONS OF THE THERMOSPHERIC VERTICAL WIND AT THE AURORAL OVAL POLAR CAP BOUNDARY/

We present further observations of thermospheric winds and temperature s, derived from observations of the lambda 630 nm oxygen auroral/airgl ow emission (from similar to 240 km altitude), obtained with a Fabry-P erot spectrometer (FPS) at Mawson station, Antarctica (L = 9). We repo rt further instances of large upward zenith winds, with velocities up to similar to 80 m s(-1), often associated with increases in temperatu re of up to 200 K. These upward winds are mostly seen around 21 Z, whi ch is when Mawson station passes under the poleward edge of the (discr ete) auroral oval during intervals of low to moderate geomagnetic acti vity, and are yet further examples of the type of event presented in a n earlier paper (Innis el ni., 1996). We also find intervals, up to se veral hours in length, when the temperatures measured South and East o f the station can be several hundred degrees higher than those measure d in the North and West directions, which we ascribe to the expansion of the hot polar cap into the South and East viewing directions. We ha ve observed examples of seemingly anomalous wind measurements in the S outh and East directions during these times, which appear to be relate d to the presence of an upward wind in the observing volume of the FPS . Our observations suggest, however, that the upward wind would cause only a small perturbation (relative to the horizontal component) of th e high-latitude thermospheric neutral wind field. The size of the zeni th wind events (up to similar to 120 m s(-1)) seen in our observations at Mawson are comparable with the amplitude of oscillations seen in g ravity waves propagating at similar to 300 km altitude over the polar cap from the nightside to the dayside, detected by Johnson er al. (199 5) from Dynamics Explorer 2 observations. This similarity and the fact that we see the upward winds at the night-time auroral oval/polar cap boundary suggest that the origin of the upward winds may be intrinsic ally linked to the processes that generate these gravity waves. (C) 19 97 Elsevier Science Ltd.