THERMOSPHERIC NEUTRAL WINDS AT SOUTHERN MIDLATITUDES - A COMPARISON OF OPTICAL AND IONOSONDE H(M)F(2) METHODS

During the first 6 days of March 1995, measurements of the ionospheric electron density were made with a digisonde, and thermospheric winds were measured with a Fabry-Perot interferometer. This was a period of low solar activity and moderate to high magnetic activity. The ionogra ms have been scaled and the traces inverted to obtain the electron den sity profile and the peak height of the F2 layer (h(m)F(2)). Modeling has been employed to derive equivalent thermospheric neutral winds at h(m)F(2). The derived neutral winds are in very good agreement with th e measured optical winds most of the time. The winds follow a strong d iurnal pattern with poleward winds during the day, weak winds near daw n and dusk, and strong equatorward winds peaking near local midnight. On most nights the peak equatorward wind speed was around 200 m s(-1), but on March 1 it did not exceed 110 m s(-1). For these magnetic and solar activity conditions the wind at the F2 peak altitude (similar to 350 km) from the HWM93 empirical wind model [Hedin et al., 1996] did not exceed 90 m s(-1) at any time but was in generally good agreement with the h(m)F(2) wind during the day and with both measured winds on the nights of March 1 and 2. The good agreement between the optical an d h(m)F(2) winds was obtained by using the recommended Burnside factor of 1.7 to multiply the O+-O collision frequency, but better agreement was obtained either by using a Burnside factor of 2.0 or by increasin g the atomic oxygen density by 20%. Recent suggestions of much lower B urnside factors could be tolerated only if there were large systematic errors in the measurements or large electric fields.