Journal of Geophysical Research, Vol.114, A07311, doi:10.1029/2009JA014091, 2009
S. Oyama(Nagoya Univ.), T. T. Tsuda(Nagoya Univ.), T. Sakanoi(Tohoku Univ.), Y. Obuchi(Genesia Co.), K. Asamura(ISAS/JAXA), M. Hirahara(Univ. of Tokyo), A. Yamazaki(ISAS/JAXA), Y. Kasaba(Tohoku Univ.), R. Fujii(Nagoya Univ.), S. Nozawa(Nagoya Univ.), and B. J. Watkins(Univ. of Alaska Fairbanks)
Abstract:
Simultaneous observation with the Sondrestrom incoherent-scatter (IS) radar and the Reimei
satellite was conducted on 3 October 2007. The objective was to measure horizontal patterns
of the ionospheric structure in the vicinity of an auroral arc. The IS radar was scanned
azimuthally with a fixed elevation angle, and the satellite narrow-view camera (557.7 nm)
was directed downward taking pictures every 0.12 s. A stationary auroral arc was captured
at 05:17 UT (02:54 MLT) with both instruments simultaneously. Gross ionospheric features
measured with the IS radar around the arc were in good agreement with the expected
magnetosphere-ionosphere current system. Of particular interest was the horizontal pattern
in the ion speed and temperature in the F region. The ion speed within the arc was close to
zero; by contrast the larger ion speed (350.400 m/s) on the poleward side was parallel to
the arc and almost no horizontal shear within about 20 km width perpendicular to the arc.
This area was separated into two parts by the ion temperature: one was associated with clear
enhancements in excess of 1200 K, and another was with more moderate enhancements (less than
1000 K). The widths of the two areas were approximately 10 km each. The horizontal shear
seen in the ion temperature suggested the presence of a narrow thermospheric wind shear of
about 10 km width. This paper suggests that the possible cause for the thermospheric wind
shear was ion drag associated with localized soft particle precipitation or F-region
ionization.
