THE INFLUENCE OF GEOMAGNETIC-ACTIVITY ON THE UPPER MESOSPHERE LOWER THERMOSPHERE IN THE AURORAL-ZONE .1. VERTICAL WINDS

A scanning Fabry-Perot spectrometer (FPS), located at Mawson station, Antarctica (67-degrees-S, 63-degrees-E, invariant latitude 70-degrees-S) was used to obtain vertical wind, temperature, and emission intensity measurements from the lambda-558 nm emission of atomic oxygen. The measured temperature is used to assign an approximate emission height to the observations. A spaced-antenna partial-reflection radar was run concurrently with the FPS from which the presence of enhanced ionization in the D-region could be inferred from the return heights and strengths of the echoes. Large upwards winds of approximately 30 m s-1, at altitudes less than 110 km, appear to be a direct response of the neutral atmosphere to intense auroral events. It is suggested that the observed upwelling is a result of particle heating at heights below the principal emission height. At higher altitudes, vertical winds of a similar magnitude are also measured during geomagnetically disturbed conditions, although here they do not appear to be associated with particular auroral events. In this case it is suggested that upwelling is produced by a combination of Joule and particle heating.