On the Source Field Geometry and Geomagnetic Induction in Southern India.

Abstract

The effect of source field geometry on the response function (ΔZ/ΔH), used in geomagnetic depth sounding to decipher lateral conductivity distribution within the earth is highlighted with the help of contour plots of ΔZ/ΔH ratios for day and nighttime short-period fluctuations recorded through a large-scale magnetometer array operated in the equatorial region of southern India. The representation of the difference between day (non-uniform) and night (uniform) time ratios in terms of the spatial derivatives of source field suggests that the reduction in daytime ΔZ/ΔH ratios at stations close to the periphery of the electrojet is due to the mutual balance of external and internal parts in ΔZ. The reduction in daytime ΔZ/ΔH ratios near the center of electrojet axis is interpreted to indicate the weakening of the intensity of induced currents due to the presence of second and higher order spatial derivatives in the non-uniform source field.