|
|
 |
|
|
Ann. Geophys., 23, 831-851, 2005
www.ann-geophys.net/23/831/2005/
© European Geosciences Union 2005
Statistical and superposed epoch study of dipolarization events using data from Wind perigee passes
K. Sigsbee1, J. A. Slavin2, R. P. Lepping2, A. Szabo2, M. Øieroset3, M. L. Kaiser2, M. J. Reiner4, and H. J. Singer5
1Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, 52242 USA
2Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
3Space Sciences Laboratory, University of California, Berkeley, California, USA
4The Catholic University of America, Washington, D.C., 20064, USA
5NOAA Space Environment Center, Boulder, Colorado, 80305 USA
Abstract. From 1995 to 2000, the Wind spacecraft spent over 500h in the
magnetotail, much of it within ~2x104km of the
predicted location of the neutral sheet. Wind passed through the near
magnetotail at distances of -15 RE<X GSM<-6 RE on 35
occasions. Another 10 passes took place at distances of -30 RE<X GSM<-15 RE.
We identified 65 dipolarization events in the Wind
magnetic field data set between Y GSM~-16 and +16 RE based
upon our requirements that the magnetic field inclination had to change by
more than 15°, the maximum inclination angle had to be greater than 20°,
and the inclination angle had to increase by a factor of at least 1.5. Most
of the dipolarization events occurred in the pre-midnight region of the
magnetotail and were accompanied by earthward flows with speeds greater than
100km/s. The properties of the dipolarization events did not depend
upon the Y GSM position. However, they did vary with the distance to the
neutral sheet. Isolated dipolarization events, defined as occurring more than
20min apart, were characterized by a decrease in Bx GSM and
BTOTAL, and an increase in Bz GSM and the magnetic field
inclination. Dipolarizations that occurred as part of a series of small
dipolarizations spaced less than 20min apart were characterized by a
transient increase in Bz GSM and the magnetic field inclination, but no
significant change in Bx GSM and BTOTAL. The events consisting of a
series of small dipolarizations occurred predominantly near midnight. We
interpret these results in terms of two different modes of magnetotail
convection: 1) a classical substorm pattern featuring storage of magnetic
energy in the tail lobes which is explosively released at onset, and 2) a
directly driven process.
Full Article in PDF (1013 KB) |
|
|
