Electric fields and currents in the equatorial electrojet deduced from VHF radar observations- II. Characteristics of electric fields on quiet and disturbed days

Abstract

Using the Doppler spectra of VHF radar signals, the height profiles of the phase velocity (V_p) of 2.7 m irregularities in the equatorial electrojet (EEJ) over Thumba (dip: 56'S) are obtained. The day-time east-west electric fields (E_y) are deduced by matching experimentally observed Vp profiles with theoretically deduced ones for a number of quiet and disturbed days. The experimental E_y values show: (i) a large day-to-day variability; (ii) a large decrease in the afternoon hours on some days (quiet and disturbed); (iii) the frequent presence of short period fluctuations with amplitudes of 30-50% of the background value and with typical time scales of 30-60 min, on moderately disturbed days (9 ≤ A_p ≤ 30); (iv) a significant decrease of the average E_y on disturbed days compared to that on quiet days during 0900-1200 h L.T.