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Title: High-latitude reconnection effect observed at the dayside dip equator as a precursor of a sudden impulse
Authors: Han, D-S.
Yang, H-G.
Araki, T.
Liang, J.
Iyemori, T.
Cowley, S. W. H.
First Published: 14-Aug-2010
Publisher: American Geophysical Union (AGU); Wiley
Citation: Journal of Geophysical Research A: SPACE PHYSICS, 2010, 115 (8)
Abstract: [1] Geomagnetic sudden impulses (SI) observed at the dayside dip equator normally show a decrease and then an increase in the H magnetic field component, i.e., a preliminary reverse impulse (PRI) followed by a main impulse. Using global geomagnetic field measurements, we examine an unusual SI event observed at the dayside dip equator, which shows a clear precursor ∼1 min before the PRI onset. The precursor was observed simultaneously at both the dayside dip equator and in the southern polar region but was not observed at all in the northern polar region. The global ground variations after the PRI onset were, however, consistent with a conventional SI model of the magnetospheric response to a sudden enhancement of the solar wind dynamic pressure. Considering that the interplanetary magnetic field Bx, By, and Bz components were positive with the By component dominant for this event, we suggest that the SI precursor was caused by high-latitude magnetic reconnection that occurred only (or first) in the dawn quadrant of the southern hemisphere, the effect of which has for the first time been clearly identified at the dayside dip equator. This implies that electric field effects occurring in the polar ionosphere due to magnetopause reconnection may be rapidly monitored at the dayside dip equator. In addition, we argue that the quasi-simultaneous (time difference is less than 10 s) appearance of the disturbance fields both in the polar region and at the dip equator confirmed in this study is extremely important for theoretically explaining the transmission of the polar electric field to the dayside dip equator, because different theories give different travel times for a disturbance field propagating from polar region to the dip equator. Our observations lend strong evidence for validity of the waveguide model.
DOI Link: 10.1029/2009JA014787
ISSN: 0148-0227
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2010 by the American Geophysical Union. All rights reserved. Archived with reference to Usage Permissions granted to authors, available at
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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