Equatorial electrojet studies from rocket and ground measurements

Combining the data of in-situ measurements of ionospheric current, J_m by rocket-borne instruments and the ground based geomagnetic H field close to the magnetic equator a linear relation has been found between the peak current density J_m and the daily range of H, (R_H). This relationship has been used to convert long series of R_H data into J_m. Combining J_m and the E-region peak electron density N_m, the electron velocity in the ionosphere, V_E has been calculated. It is shown that after all corrections are made of the solar zenith angle variations, the ionospheric current as well as electron drift in American and Indian sectors show strong equinoctial maxima, the mean values of both the parameters are larger at American than in Indian sector. The solar cycle variation of the electrojet current is primarily due to the variations of N_mE, and not due to the variations of electric field. The diurnal variation of the electric field with peak at 09–10 LT interacting with noon peak of N_mE making ΔH to peak at an hour earlier than noon. It is stressed to realise the importance of electric field in diurnal, seasonal and longitudinal variations of the equatorial electrojet current.