A CME loop and the January 10, 1997 first substorm

B. T. Tsurutani, J. K. Arballo, G. S. Lakhina, C. M. Ho, J. M. Ajello, J. S. Pickett, D. A. Gurnett, R. P. Lepping, W. K. Peterson, G. Rostoker, Y. Kamide and S. Kokubun

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California


The January 10, 1997 interplanetary high-speed stream and the resultant first substorm (~0332 to 0334 UT onset) is studied using Wind interplanetary data and Polar UV images, respectively. A 47 minute interval of relatively intense southward interplanetary magnetic field (IMF) (BS = 4 to 8 nT, where BS is the southward component of the IMF) bounded by two tangential discontinuities (TDs) is identified sunward of the interplanetary shock and anti-sunward of the magnetic cloud. The TD orientations are used to calculate the solar wind delay times from Wind to the Earth's magnetopause. The estimated arrival times are in excellent agreement with Geotail data (the two discontinuities occurred at 0219 and 0302 UT at Geotail). The IMF BS event serves primarily to transfer solar wind energy to the magnetosphere/magnetotail, as no substorm expansion phase occurs during the event. The interplanetary BS event comes after a prolonged northward IMF interval. During the initial part of the BS event, both polar cap Sun-Earth aligned arcs formed (part of a theta aurora) and an auroral hot spot along the main arc took place. During this initial interval, an aurora in the shape of a horseshoe developed at a lower (60° ) latitude (an oval with a gap in the noon sector). The dawnside portion of the horseshoe aurora became much brighter than the duskside with increasing time. The dawnside polar cap boundary layer (PCBL) broadband waves were well correlated with low energy ion fluxes (H+, He++, O+) during the event. It is speculated that this IMF BS structure may be an outer loop of the CME coming from the Sun. Another similar loop is identified just adjacent to the cloud.

SUBSTORM-4, 309-314, 1998