Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

i V.P. Perevalova al al. Geographic Coordinates G eomagnetic longitude: • 0 ° ж l 5 ° и » “* > 4 2 5 5 * 105° n n Y 4 2 S ^ V ; ч> x / , V ( b ^ L » У ™ , д 165» 120 \ V Г Ч Й Т ' £ W 240 ^ \ / ^ ^ - _ o i - ^ гЪ у * ' 4v C 1 8 r 1 3 s \ > ^ ' - , i V / 2 2 5 X 240° ' - 1- V r \ □I 270° 150 — I ___A - - ^ 210 ★ 285° 165 180 195 Fig. 2. Travel o f points moving along nine geomagnetic meridians (0°, 15°, 90°, 105°, 165°, 180°, 240°, 270°, 285°) in the geographic coordinate system Calculation of the velocity and travel direction of the LS TIDs during different magnetic storms have repeatedly been made by the Institute of Solar- Terrestrial Physics SB RAS (Irkutsk, Russia). It was shown that in the Northern Hemisphere LS TIDs do not travel strictly southwards, but south-westwards as a rule, or south-eastwards in certain cases [Leonovich et al., 2004; Perevalova et al., 2008]. The velocity and travel direction of the LS TIDs exhibit a strongly pronounced longitudinal dependence, which is usually related with the local time (LT). During the 29 October 2003 magnetic storm [Perevalova et al., 2008] the LS TID propagation direction in the night and day sectors was close to meridional; in the morning and evening sectors the zonal component o f LS TID velocity exceeded the meridional one. The smallest LS TID velocity (700 m/s) was detected in the night region, the highest (1600 m/s) on the day side. During a strong magnetic storm on 25 September 1998 [Afraimovich et a l, 2000] the azimuth of the LS TID wave vector varied in North America along the wavefront from 245° at the longitude corresponding to 1600 LT to 177 0 at the longitude corresponding to 1900 LT. Toward the local nighttime, the propagation direction was nearly equatorward. Analysis of LS TID propagation directions during five magnetic storms of 1998-2001 [Leonovich et al., 2004] showed that south-westward direction (198±25°) predominated on the Earth dayside with a south-eastward (169±20°) prevailing on the night side. The LS TID propagation velocities on the night side (970±300 m/s) were higher then those on the dayside (660±200 m/s). Many other authors also mentioned the westward displacement (by 10-20° on average) o f the LS TID propagation direction [Maeda and Handa, 1980; Balthazor and Moffett, 1999; Hall et al., 1999; Foster et al., 1989]. The causes o f the LS TID deviation from the equatorward propagation direction are not exactly known. Possible causes include Coriolis force effect, thermospheric winds, a powerful stream o f plasma ejected from polar cap. However, one of the causes may lie in the calculation technique involved. One can expect that in the absence of deviating factors wave LS TID generated at the southern boundary of the auroral oval should propagate radially from a source, i.e. along the geomagnetic meridian. Calculating the LS TID velocity in geographic coordinate systems, can lead to certain distortions. The purpose o f this paper is to conduct comparative analysis o f the motion parameters (travel direction and velocity) of auroral LS TIDs in the geomagnetic 38