A Comparison of The Location of The Central Meridian of Substorm Current Wedge 
with Auroral Images and Geosynchronous Observations

Hsu, T., McPherron, R., Lee, B.


One of the major difficulties in determining the spatial extent of current
disruption associated with the substorm current wedge is due to the fact that
satellites are rarely positioned properly to distinguish azimuthal from radial
structures. Even if we observe a time delay between dipolarization signatures at
two satellites located close to each other, it is sometimes difficult to
determine whether this time delay is due to radial or azimuthal expansion of the
tail current disruption associated with the substorm current wedge. In order to
accurately determine the dipolarization onset time, it is necessary to know
where the satellite is positioned relative to the substorm current wedge.
Several methods can help us to determine the central meridian of substorm
current wedge. The easiest one uses the auroral images. The bright surge like
western termination of the bulge is associated with the upward field-aligned
current. The comparison of auroral images from the IMAGE and POLAR UVI
satellites can give us a crude estimation of where the substorm current wedge is
located relative to the GOES satellites. However, a more convenient method is to
invert ground magnetometer data to obtain the parameters of a model current
system that gives the best fit to the observed magnetic perturbations. The model
currents include three components: the substorm current wedge, symmetric ring
current and partial ring current. This inversion method is capable of obtaining
the intensity as well as the longitudinal boundaries of the substorm current
wedge with accuracy better than 0.5 hour MLT. There are more than 40
mid-latitude stations available during fall 2001 and 2002. MEASURE, SMALL, 210
MM and INTERMAGNET are arrays with many stations. We have established a substorm
onset list for the fall 2001. This substorm list will be used as a basis for the
development of the inversion code to determine the central meridian of substorm
current wedges. The estimated central meridian of substorm current wedge will be
compared with auroral images and geosynchronous observations. The accuracy and
relative timing between these observations will be examined.

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Fall Meeting, American Geophysical Union, San Francisco, U.S.A., 
5-9 December 2005