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Title: Daytime equatorial geomagnetic H field response to the growth phase and expansion phase onset of isolated substorms: Case studies and their implications
Authors: Sastri, J. H
Rao, J. V. S. V
Rao, D. R. K
Pathan, B. M
Keywords: Isolated Substorms;Interplanetary Magnetic Field (IMF);Ionospheric Currents;Magnetospheric Convection
Issue Date: Dec-2001
Publisher: American Geophysical Union
Citation: Journal of Geophysical Research-Space Physics, Vol. 106, No. A12, pp. 29925 – 29933
Abstract: Observations are presented from the Indian magnetometer network (dipole latitude range 1.2°S to 13.5°N) of short-lived (<1 hr) disturbances in the daytime equatorial geomagnetic H field associated with specific phases of isolated substorms. Three well-documented substorms are examined here, of which the expansion onset of each is closely associated with sudden transitions of interplanetary magnetic field (IMF) Bz /By after a >40-min interval of southward Bz . A positive baylike perturbation is found to prevail during the substorm growth phase, followed by a negative baylike disturbance starting precisely at the onset of expansion phase activity. The amplitude of the positive as well as negative bay-type disturbance showed a clear-cut enhancement at locations inside the equatorial electrojet belt when compared with stations away from the electrojet influence, indicative of a significant contribution of ionospheric currents to the bays. This pattern of response, which is found in two out of the three events studied, constitutes the first-time evidence for the occurrence of equatorial H field perturbations related to the growth phase as well as the expansion phase onset for individual substorms. The H field perturbations are suggested to be signatures of prompt penetration by electric fields associated with rapid changes in magnetospheric convection brought about by the swift transitions in the IMF Bz , before shielding by the ring current becomes effective. In the third event, where the growth phase is weak and prolonged, there is no perceptible simultaneous disturbance in the equatorial H field, while the expansion phase onset is associated with a positive bay of very small amplitude (≤4 nT).
Description: Open Access
ISSN: 0148-0227
Appears in Collections:IIAP Publications

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