MEASUREMENTS OF EQUATORIAL MAGNETIC DIP ANGLE AT IONOSPHERIC HEIGHTS

Abstract

Abstract : Data collected for calculating electron content of the ionosphere by the Faraday rotation technique can be used to calculate the magnetic dip angle at ionospheric height near the geomagnetic dip equator. In this report the magnetic dip angle at ionospheric height was determined at the position where the angle between the ray path from the satellite to the ground station and the geomagnetic field vector is 90 degrees (transverse position). The magnetic dip angle calculation was based on the assumption of a constant height of 350 km for the centroid of the ionospheric electron-density profile. The spherical harmonic analysis is used to verify the experimental results. The results compare well with the surface magnetic dip angle, measured in 1956-1960 by the Geodesy Department of the Ministry of Defense, Thailand, and indicate that the magnetic dip angle at ionospheric height is very close to the surface value. These data permit estimation of the position of the geomagnetic dip equator at the ionospheric height. The estimated position of this equator is directly above the geographic latitude of 9.30 degrees N. This latitude intersects the southern peninsula of Thailand about 480 km south of Bangkok (near Surat Thani). This estimated value compares well with the surface geomagnetic dip equator and indicates that the dipole field is a good model for Southeast Asia in the vicinity of longitude 100 degrees E.