Seasonal Variations of Geomagnetic D, H and Z Fields at Low Latitudes

Abstract

The extensive set of geomagnetic data at nine observatories in India covering region of magnetic dip angle 0° to 50°N and a period of 1975 to 1986 have shown that the equinoctial maxima in the geomagnetic field are observed only on the horizontal and vertical components at the electrojet observatories, for the local hours around the peak current density and are consequent to the seasonal and daily changes of the equatorial electrojet current. The eastward component of the geomagnetic field shows predominantly annual variation with maximum during summer months at any of the stations. These observations exclude the seasonal changes of solar ionisation effects to either axial theory of CORTIE (1912) or the equinoctial theory of BARTELS (1932). The equatorial stations are suggested to be affected by the imposition of east-west electric field in addition to that generated by the dynamo action of the earth's ionosphere. The most plausible source of these additional electric field arise out of the action of solar wind and interplanetary magnetic field with the magnetosphere.