VHF backscatter radar observations of the equatorial electrojet irregularities - diurnal, seasonal and solar cycle variations

VHF backscatter radar observations at Thumba, for the period 1974-1982, are used to study the diurnal, seasonal and solar cycle variations of the Doppler frequency of the Doppler frequency of the backscatter echoes from the 2.7 m scale size ionization iregularities in the equatorial electrojet. The study shows that the Doppler frequency exhibits strong diurnal, seasonal and solar activity dependences. Also, it is seen that the average characteristics of the Doppler frequency variations are in broad agreement with the observed Delta-H variations at Trivandrum. A discussion is given on the constraints under which the observed Doppler frequency variations can be regarded as representing the corresponding variations in the electric fields of the equatorial electrojet

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

Using the Doppler spectra of VHF radar signals, the height profiles of the phase velocity (Vp) of 2.7 m irregularities in the equatorial electrojet (EEJ) over Thumba (dip: 56'S) are obtained. The day-time east-west electric fields (Ey) are deduced by matching experimentally observed Vp profiles with theoretically deduced ones for a number of quiet and disturbed days. The experimental Ey 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 ≤ Ap ≤ 30); (iv) a significant decrease of the average Ey on disturbed days compared to that on quiet days during 0900-1200 h L.T