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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 10
Ann. Geophys., 15, 1301–1308, 1997
© European Geosciences Union 1997
Ann. Geophys., 15, 1301–1308, 1997
© European Geosciences Union 1997

  31 Oct 1997

31 Oct 1997

An intense SFE and SSC event in geomagnetic H, Y and Z fields at the Indian chain of observatories

R. G. Rastogi1,*, D. R. K. Rao2, S. Alex2, B. M. Pathan2, and T. S. Sastry3 R. G. Rastogi et al.
  • 1Department of Physics, Gujarat University, Ahmedabad 380 009, India
  • 2Indian Institute of Geomagnetism, Mumbai 400 005, India
  • 3National Geophysical Research Institute, Hyderabad 500 007, India
  • *Presently at: School of Physics, University of New South Wales, Sydney, Australia

Abstract. Changes in the three components of geomagnetic field are reported at the chain of ten geomagnetic observatories in India during an intense solar crochet that occurred at 1311 h 75° EMT on 15 June 1991 and the subsequent sudden commencement (SSC) of geomagnetic storm at 1518 h on 17 June 1991. The solar flare effects (SFE) registered on the magnetograms appear to be an augmentation of the ionospheric current system existing at the start time of the flare. An equatorial enhancement in ΔH due to SFE is observed to be similar in nature to the latitudinal variation of SQ (H) at low latitude. ΔY registered the largest effect at 3.6° dip latitude at the fringe region of the electrojet. ΔZ had positive amplitudes at the equatorial stations and negative at stations north of Hyderabad. The SSC amplitude in the H component is fairly constant with latitude, whereas the Z component again showed larger positive excursions at stations within the electrojet belt. These results are discussed in terms of possible currents of internal and external origin. The changes in the Y field strongly support the idea that meridional current at an equatorial electrojet station flows in the ionospheric dynamo, E.

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