Results from in situ Measurements of Ionospheric Currents in the Equatorial Region-I

Several rocket borne magnetometer experiments have been conducted from Thumba to measure the equatorial electrojet currents under different solar and geophysical conditions. The data from these experiments have been used to study the vertical structure of the electrojet, the relation between strength of the jet and the magnetic field variation at the ground and the causes of large day-to-day variability of the amplitude of H variation. The results show that the experimentally measured current density peaks at a significantly different altitude compared to the altitude of the peak of Cowling conductivity calculated using model values of ionospheric parameters. The analysis indicates that given the magnetogram from a station under the electrojet, it is possible to predict the vertical distribution of current density in the electrojet on a quiet day. The mechanism of stabilisation of two stream instability suggested by the theoretical workers ro explain the back scatter radar echoes from type I irregularities on high jet days does not become operative atleast upto jet strengths equivalent to ΔH≤140nT.