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Ann. Geophys., 18, 1154-1163, 2000
www.ann-geophys.net/18/1154/2000/
© European Geosciences Union 2000
Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region
S. Oyama1, S. Nozawa2, S. C. Buchert2, M. Ishii1, S. Watari1, E. Sagawa1, W. Kofman3, J. Lilensten3, and R. Fujii2
1Communications Research Laboratory, 4-2-1, Nukuikita-machi, Koganei, Tokyo, 184-8795, Japan
2Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
3Laboratoire de Planetologie de Grenoble Batiment D de Physique BP 53, 38041 Grenoble Cedex, France
Abstract. The field-aligned neutral oscillations in the
F-region (altitudes between 165 and 275 km) were compared using data
obtained simultaneously with two independent instruments: the European
Incoherent Scatter (EISCAT) UHF radar and a scanning Fabry-Perot interferometer
(FPI). During the night of February 8, 1997, simultaneous observations with
these instruments were conducted at Tromsø, Norway. Theoretically, the
field-aligned neutral wind velocity can be obtained from the field-aligned ion
velocity and by diffusion and ambipolar diffusion velocities. We thus derived
field-aligned neutral wind velocities from the plasma velocities in EISCAT radar
data. They were compared with those observed with the FPI (λ=630.0
nm), which are assumed to be weighted height averages of the actual neutral
wind. The weighting function is the normalized height dependent emission rate.
We used two model weighting functions to derive the neutral wind from EISCAT
data. One was that the neutral wind velocity observed with the FPI is velocity
integrated over the entire emission layer and multiplied by the theoretical
normalized emission 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
instruments had peak-to-peak correspondences at oscillation periods of about
10–40 min, shorter than that for the momentum transfer from ions to neutrals,
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 oscillations rather than
the transfer from ions to neutrals. It is concluded that during 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.
Key words: Ionosphere (Ionosphere–atmosphere
interactions) – Meteorology and atmospheric dynamics (thermospheric dynamics;
waves and tides)
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