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.

Ionospheric disturbances generated in the auroral zone during magnetic storms. and geographic coordinate systems. The analysis is based on a simulation of the point motion in these coordinate systems. 2. Simulation of the motion of points in the geomagnetic and geographic coordinate systems We carried out the simulation to find out how a point (having certain velocity components in latitude and longitude in the geomagnetic coordinate system) moves in the geographic coordinate system. It was suggested that the point moved along the geomagnetic meridian with velocity Vr =617 m/s. The chosen value Vr corresponded to the average velocity of travel of LS TIDs during magnetic storms. We simulated the motion o f nine points along meridians with longitudinal values of 0°, 15°, 90°, 105°, 165°, 180°, 240°, 270°, 285°. Fig. 1 presents the successive positions of points that moved along geomagnetic meridians. The distance between the successive positions was 5°. At velocity Vr = 617 m/s, the point travelled this distance in about 15 minutes. Grey arrows in Fig. 1 indicate the directions of velocity Vr for some magnetic meridian. The Zero Magnetic Meridian is marked by thick black line. The geomagnetic coordinates of the point successive positions were converted to their geographic coordinates, thus obtaining a visible motion of points in geographic coordinate systems. Fig. 2 shows the Meridional Component Vr, m/s 640 • 540 - 440 — 340 — 240 — 140 - 80 I 70 V=617 m/s ~r • 00 ° ■ 90° A 15° T— I derived position of the same points in the geographic coordinate system. According to calculations, the velocity of the point in the geographic system has two components: along the geographic meridian (meridional component, Vr) and geographic parallel (zonal component, Уф). The meridional component reflects changes in latitude of the travelling point; the zonal component, changes in its longitude. The directions of Vr and Уф are shown by grey arrows. A thick black line in Fig. 2 marks the positions of the Zero Magnetic Meridian. At meridians with a geomagnetic longitude of 0° and 180°, the zonal velocity component Уф in geographic coordinates is equal to zero. This is a result of the Geographic North Pole been located at the Zero Magnetic Meridian. At meridians with the geomagnetic longitude of 90° and 270°, Уф reaches its maximum value. At geomagnetic longitudes 0° to 180°, the zonal velocity component Уф is eastward. At geomagnetic longitudes 180° to 360°, the zonal velocity component is westward. The values of meridional Vr and zonal Уф components at the various geographic latitudes are displayed in Fig. 3. The symbols designate latitude variations of Vr and Уф at geomagnetic meridians 0° and 180r (dots), 90° and 270° (squares), 15° and 240° (triangles). The positive values correspond to eastward Уф. A solid black line in the left side of Fig. 3 marks the meridional velocity Vr = 617 m/s in the geomagnetic coordinate system. The zonal V m/s 500 - 400 — 300 - 200 — 100 — 0 - Zonal Component Eastward С • оо о A 15° ■ о О 0\ ■ ■ и A A A -i— |# i # |# m I» i 60 50 40 30 80 70 60 50 40 30 Vr, m/s 640 — 540 440 — 340 240 140 ' .....Г... T 80 1— [---- 1---- |---- I 70 60 50 40 Geographic latitude , 0 180° 270° 240° “ I Ф’ m/s о — -100 — -200 — -300 - -400 - -500 - Westward * * * * * * ■ • 18(0° 270° 240° T 30 80 30 1 1 I I I I I 70 60 50 40 Geographic latitude , 0 Fig. 3. Values of meridional Vr (at the left) and zonal Уф (at the right) components of point velocity in the geographical coordinate system at the geomagnetic meridians with longitudes: 0° and 180° (dots), 90° and 270° (squares), 15° and 240° (triangles). Positive values correspond to eastward Уф. 39