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Ann. Geophys., 24, 3481-3490, 2006
www.ann-geophys.net/24/3481/2006/
© European Geosciences Union 2006
A statistical study of magnetic dipolarization for sawtooth events and isolated substorms at geosynchronous orbit with GOES data
X. Cai1, M. G. Henderson2, and C. R. Clauer1
1Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA
2Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Abstract. We investigate whether the dipolarization process during
sawtooth events is global or not through an examination of the local time
distribution of the magnetic tilt angle (i.e. the angle between the B
vector and the equatorial plane in dipole VDH coordinates) at
geostationary orbit. From the statistical analysis of 207 individual teeth and
212 isolated substorms, we find that individual teeth follow a dipolarization
pattern similar to that observed for isolated substorms. The dipolarization for
individual teeth initiates in the sector between 22:00 magnetic local time
(MLT) and 00:00 MLT. Then the dipolarization expands both eastward and
westward. However, relative to isolated substorms, we find that the nightside
magnetosphere is much more stretched prior to the onset, and the change of the
tilt angle during the dipolarization process is much larger during individual
teeth. The magnetic dipolarization is seen over a wider local time sector
during individual teeth than during isolated substorms. However, the magnetic
dipolarization is rarely observed near local noon during individual teeth. This
suggests that the magnetic dipolarization process during individual teeth is
still confined primarily to the nightside.
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