Letter | Open | Published:
Response of the equatorial electrojet to solar flare related X-ray flux enhancements
Earth, Planets and Spacevolume 57, pages231–242 (2005)
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°N, 77°E; dip 0.5°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 (σ2) to the field line integrated Pedersen conductivity (σ1) in the dynamo region 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.
Balsley, B. B., Electric fields in the equatorial ionosphere: A review of techniques and measurements, J. Atmos. Terr. Phys., 35, 1035–1044, 1973.
Banks, P. M. and G. Kockarts, Aeronomy, Part A., Academic press, New York, 1973.
Chapman, S., Regular motions in the ionosphere: Electric and magnetic relationships, Bull. Amer. Meteorol. Soc., 42, 85, 1961.
Donelly, R. F., An analysis of sudden ionospheric disturbances associated with the proton flare of 1522 UT, Aug. 28, 1966, ESSA Tech. Rep. ERL 92-SDL6, U. S. Government printing office, Washington, D. C., 1968.
Farley, D. T. and B. B. Balsley, Instabilities in the equatorial electrojet, J. Geophys. Res., 78, 227, 1973.
Fejer, B. G. and M. C. Kelly, Ionospheric irregularities, Rev. Geophys. And Space Phys., 18, 401, 1980.
Mitra, A. P. and S. D. Despande, Flaretime models of ionisation profiles in the D region, Space Research XII, Akademic, Verlag, Berlin, 1291, 1972.
Mitra, A. P. and C. V. Subrahmanyam, Sudden ionospheric disturbances, Ind. J. Rad. Space Phys., 1, 93, 1972.
Oshio, M., N. Fukushima, and T. Nagata, Solar flare effects on geomagnetic field, Rep. Ionos. Space Res. Japan, 21, 77–114, 1967.
Rangarajan, G. K. and R. G. Rastogi, Solar flare effect in equatorial magnetic field during morning counter electrojet, Ind. J. Rad. Space Phys., 10, 190–192, 1981.
Rastogi, R. G., Solar flare effects on zonal and meridional currents at the equatorial electrojet station, Annamalainagar, J. Atmos. Terr. Phys., 58, 1413–1420, 1996.
Rastogi, R. G., M. R. Deshpande, and N. S. Sastri, Solar flare effect in equatorial counter electrojet current, Nature (London), 258, 218–219, 1975.
Rastogi, R. G., D. R. K. Rao, S. Alex, B. M. Pathan, and T. S. Sastry, An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian Observatories, Ann. Geophys., 15, 1301–1308, 1997.
Rastogi, R. G., B. M. Pathan, D. R. K. Rao, T. S. Sastry, and J. H. Sastri, Solar flare effects on the geomagnetic elements during normal and counter electrojet periods, Earth Planets Space, 51, 947–957, 1999.
Reddy, C. A., V. V. Somayajulu, and K. S. Viswanathan, The lunar phase and the equatorial electrojet, Low latitude aeronomical processes, COSPAR Symp. Ser., edited by A. P. Mitra, Pergamon, New York, 29, 1980.
Reddy, C. A., B. T. Vikramkumar, and K. S. Viswanathan, Electric fields and currents in the equatorial electrojet deduced from VHF radar observations—I. A method of estimating electric fields, J. Atmos. Terr. Phys., 49, 183, 1987.
Richmond, A. D., Equatorial electrojet. I. Development of a model including winds and instabilities, J. Atmos. Terr. Phys., 35, 1083–1103, 1973a.
Richmond, A. D., Equatorial electrojet. II. Use of the model to study the equatorial ionosphere, J. Atmos. Terr. Phys., 35, 1105–1118, 1973b.
Sampath, S. and T. S. G. Sastry, Results from in situ measurements of ionospheric currents in the equatorial region, J. Geomag. Geoelectr., 31, 373, 1979.
Sastri, J. H., The geomagnetic solar flare effect of 6 July 1968 and its implications, Ann. Geophys., 31, 481, 1975.
Sato, T., The response of the lower ionosphere to the great solar flare of August 7, 1972, J. Geomag. Geoelectr., 27, 383, 1975.
Srivastava, B. J., The geomagnetic solar flare effect of 03 May 1973 at Indian stations and its dependence on the counter electrojet, J. Atmos. Terr. Phys., 36, 1571, 1974.
Subbaraya, B. H., S. Prakash, and S. P. Gupta, Electron densities in the equatorial lower ionosphere from the Langmuir probe experiments conducted at Thumba during the years 1966–1978, ISRO-PRL Special Report, ISRO-PRL-SR-15-83, 1983.
Thome, G. D. and L. S. Wagner, Electron density enhancements in the E and F regions of the ionosphere during solar flares, J. Geophys. Res., 76, 6883, 1971.
Van Sabben, D., Solar flare effects and simultaneous magnetic daily variation, J. Atmos. Terr. Phys., 30, 1641, 1968.
Viswanathan, K. S., Study of electrodynamics of the equatorial electrojet, Ph.D. thesis, University of Kerala, India, 1986.
Yasuhara, M. and H. Maeda, Geomagnetic Crochet of 15 November 1960, J. Atmos. Terr. Phys., 21, 289, 1961.