APPENDIX: MAGNETOSPHERE In this appendix, we shall give a brief description of the relevant features of the magnetospheric environment. In the process, the reader is introduced to the technical terms used in the text. The solar wind, a supersonic plasma flow (typical density ~ 8 cm-3 and speed ~ 300 km/sec at earth orbit) away from the sun, is deflected by the earth’s magnetic field at a standoff distance of ~ 10 RE in the sunward direction. Equivalently, the earth’s magnetic field is said to be confined to a cavity called the magnetosphere by the solar wind (Figure A1). On the night side, the magnetospheric cavity extends some hundreds of earth radii downstream where present evidence seems to indicate a merging of the earth’s magnetic field lines with that of the solar wind magnetic field. This geomagnetic tail region is bisected near the equatorial plane by the neutral sheet where the magnetic field lines originating from the north and south polar caps cancel each other creating a dawn-dusk current sheet (Figure Al). The electric field (dawn-dusk) associated with this current sheet is called the convection electric field because the hot plasma in the vicinity of the neutral sheet (plasma sheet) is convected sunward by the [[spi:math]] force. The earthward end of the plasma sheet is connected by magnetic field line to the auroral zones. In the course of a magnetic storm, solar wind plasma enters into the plasma sheet and is driven earthward on the night side by the increased convection electric field, forming a ring current of hot plasma in the vicinity and earthward of GEO, where SPS is stationed (Figures A2). Precipitation of the hot ring current plasma along dipole-like magnetic field lines into the auroral zone causes atmospheric airglow at ~ 100 km altitude known as the A-l
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