Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa72b0541o&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SA72B-0541
Physics
2400 Ionosphere, 2407 Auroral Ionosphere (2704), 2437 Ionospheric Dynamics, 3369 Thermospheric Dynamics (0358), 3384 Waves And Tides
Scientific paper
We focus on field-aligned ion motions around the boundary between polar ionospheric E- and F-regions (from 140 to 250 km heights). Here we define a "transient region" as the boundary. Ionospheric parameters were obtained with the European Incoherent Scatter (EISCAT) Kiruna-Sodankylä-Troms\o (KST) UHF radar (931 MHz, 69.35°N, 19.14°E, 66.12° invariant latitude) in northern Scandinavia. The observation mode of the KST radar was so-called Common Program One (CP-1) mode where the antenna at Troms\o is pointed along the local magnetic field line there. This mode provides us with ion velocity, electron density, and electron and ion temperatures with high time- (order of minutes) and altitude- (about 3 km) resolutions along the radar beam. In addition, this mode conducts a tristatic measurement of ion velocity at 278 km thus the electric field vector assuming ExB drift. We used EISCAT data sets obtained for about one solar cycle (~ 11 years). In order to get an overview of the spectral behavior of the variations in field-aligned ion motions, a Lomb periodgram and a Fast Fourier Transform (FFT) were applied to EISCAT radar data sets that were selected every 24 hour intervals. The reason why we used two spectral analysis methods was to estimate effects of gaps in EISCAT radar data. Results from both spectral analysis showed that dominant oscillation periods at the lower (upper) region of transient region was 12 (24) hours. The phase and amplitude of 24/12 hours variations in the field-aligned ion velocity in the transient region had similar height profiles to those of thermospheric tide predicted by model calculation (Forbes, 1982) when electric field magnitude observed with the EISCAT radar was relatively small. Directions and magnitude of height gradient of field-aligned ion velocity in the transient region had also 24- and 12-hours periodic oscillations. These tendencies were dominant regardless of electric field magnitude. Because the pressure gradient force along the magnetic field line was considerably small to accelerate ions up to observed level even during high auroral activity (Fujii et al., 2002), thermospheric tidal motions could be a major cause that maintained the 24- and 12-hours oscillations of field-aligned ion velocity. Amplitude and phase of 24- and 12-hours oscillations strongly depended on the electric field magnitude. This suggests that electromagnetic force such as ion drag and pressure gradient caused by Joule and particle heating can generate and/or modulate thermospheric tides in the transient region. Forbes, Atmospheric tides 2. The solar and lunar semidiurnal components, JGR, 87, 5241-5252, 1982. Fujii, R., S. Oyama, S. C. Buchert, S. Nozawa, and N. Matuura, Field-aligned ion motions in the E and F regions, JGR, 107, A5, 2002.
Fujii Ryoichi
Murayama Yuko
Nozawa Satoshi
Oyama Satoshi
Shinagawa Hiroyuki
No associations
LandOfFree
Field-aligned Ion Motions in the Transient Region between Polar Ionospheric E- and F-regions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Field-aligned Ion Motions in the Transient Region between Polar Ionospheric E- and F-regions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Field-aligned Ion Motions in the Transient Region between Polar Ionospheric E- and F-regions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1434598