Response of the equatorial electrojet to solar flare related X-ray flux enhancements

The response of ionospheric E-region electric fields and currents to solar flare related X-ray flux enhancements are studied at the magnetic equatorial location of Trivandrum (8.5 degrees N, 77 degrees E; dip 0.5 degrees N) using VHF (54.95 MHz) coherent backscatter radar observations in the altitude region of 95-110 km conducted during daytime. The amplitude of the Solar Flare Effects (SFE) observed in the earth's magnetic field variations at Trivandrum have been examined in relation to that at Alibag and it is found that the ratio of the SFE amplitudes at the two stations lies in the range of 1.8-2.6. The backscattered power of the VHF radar showed a substantial reduction during the peak phase of all the strong X-rank flares studied. It has also been observed that there is a sharp fall in the ratio of the field line integrated Hall conductivity (sigma(2)) to the field line integrated Pedersen conductivity (sigma(1)) in the dynamo region (integral sigma 2ds vertical bar integral sigma(1)ds) during strong flare times in relation to normal times. The time variations of mean Doppler frequency (f(D)) of the backscattered signals have been observed to indicate a fall close to the peak phase of the strong flare events. Another new result is the radar observed presence of westward electric field for a long duration of 2-3 hours during a partial counter electrojet (CEJ) event that occurred on one of the days (8 July 1992) Studied. The implications of the observations are discussed in detail.