Longitudinal variation in the equatorial electrojet

Abstract

The enhancement of the diurnal range of the horizontal component (H) of the earth's magnetic field over the magnetic equator, believed to be due to the equatorial electrojet, is shown to be most pronounced in the American Zone and least in the Indian Zone, using the data contained in EDGEDAL'S report to IATME, observations by PRAMANIK et al. for the Indian zone, and the data at various other observatories collected during the IGY. The maximum value of the diurnal range in Hin each of the zones occurs at a station closer to the magnetic rather than to the geomagnetic or the geographic equator. An approximately inverse relationship is found to exist between the diurnal range and the average value of H at the magnetic equator. The longitudinal variation of the ionospheric conductivities due to the varying intensity of the earth's magnetic field over the magnetic equator, is found to be too small to explain the longitudinal inequalities in the electrojet. Non-uniformities in the distribution of tidal velocities and/or of ionization densities in the ionosphere over different parts of the earth seem, therefore, to be necessary to produce the observed longitudinal variation in the equatorial electrojet.