Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region

The field-aligned neutral oscillations in the F-region (altitudes between 1 65 and 275 km) were compared using data obtained simultaneously with two in dependent instruments: the European Incoherent Scatter (EISCAT) UHF radar a nd a scanning Fabry-Perot interferometer (FPI). During the night of Februar y 8, 1997, simultaneous observations with these instruments were conducted at Tromso, Norway. Theoretically, the field-aligned neutral wind velocity c an be obtained from the field-aligned ion velocity and by diffusion and amb ipolar diffusion velocities. We thus derived field-aligned neutral wind vel ocities from the plasma velocities in EISCAT radar data. They were compared with those observed with the FPI (lambda = 630.0 nm), which are assumed to be weighted height averages of the actual neutral wind. The weighting func tion is the normalized height dependent emission rate. We used two model we ighting functions to derive the neutral wind from EISCAT data. One was that the neutral wind velocity observed with the FPI is velocity integrated ove r the entire emission layer and multiplied by the theoretical normalized em ission rate. The other was that the neutral wind velocity observed with the FPI corresponds to the velocity only around an altitude where the emission rate has a peak. Differences between the two methods were identified, but not completely clarified. However, the neutral wind velocities from both in struments had peak-to-peak correspondences at oscillation periods of about 10-40 min, shorter than that for the momentum transfer from ions to neutral s, but longer than from neutrals to ions. The synchronizing motions in the neutral wind velocities suggest that the momentum transfer from neutrals to ions was thought to be dominant for the observed field-aligned oscillation s rather than the transfer from ions to neutrals. It is concluded that duri ng the observation, the plasma oscillations observed with the EISCAT radar at different altitudes in the F-region are thought to be due to the motion of neutrals.