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Ann. Geophys., 20, 1647-1661, 2002
www.ann-geophys.net/20/1647/2002/
© European Geosciences Union 2002
Velocities of auroral coherent echoes at 12 and 144 MHz
A. V. Koustov1,3, D. W. Danskin1, M. V. Uspensky2,4, T. Ogawa3, P. Janhunen2, N. Nishitani3, S. Nozawa3, M. Lester5, and S. Milan5
1Institute of Space and Atmospheric Studies, University of Saskatchewan, 116 Science Place, Saskatoon, S7N 5E2 Canada
2Finnish Meteorological Institute, Vuorikatu 15A, P.O. Box 503, Helsinki FIN-00101, Finland
3Solar-Terrestrial Environment Laboratory, Nagoya University, 3–13 Honohara, Toyokawa, Aichi 442, Japan
4Murmansk State Technical University, Sportivnaya 13, Murmansk, 183010 Russia
5Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH UK
Correspondence to: A. V. Koustov
(koustov@dansas.usask.ca)
Abstract. Two Doppler coherent radar systems are
currently working at Hankasalmi, Finland, the STARE and CUTLASS radars
operating at ~144 MHz and ~12 MHz, respectively. The STARE beam 3 is nearly
co-located with the CUTLASS beam 5, providing an opportunity for echo velocity
comparison along the same direction but at significantly different radar
frequencies. In this study we consider an event when STARE radar echoes are
detected at the same ranges as CUT-LASS radar echoes. The observations are
complemented by EISCAT measurements of the ionospheric electric field and
electron density behaviour at one range of 900 km. Two separate situations are
studied; for the first one, CUTLASS observed F-region echoes (including the
range of the EIS-CAT measurements), while for the second one CUTLASS observed
E-region echoes. In both cases STARE E-region measurements were available. We
show that F-region CUT-LASS velocities agree well with the convection component
along the CUTLASS radar beam, while STARE velocities are typically smaller by a
factor of 2–3. For the second case, STARE velocities are found to be either
smaller or larger than CUTLASS velocities, depending on the range. Plasma
physics of E-and F-region irregularities is discussed in attempt to explain the
inferred relationship between various velocities. Special attention is paid to
ionospheric refraction that is important for the detection of 12-MHz
echoes.
Key words. Ionosphere (ionospheric irregularities;
plasma waves and instabilities; auroral ionosphere)
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