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			 **   THE GEM MESSENGER   **
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						     Volume 13, Number 27
						     July 16, 2003

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Report on Combined Working Group on Substorm Observations and
Triggering (Tail/Substorm Campaign) at the GEM 2003 Workshop
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From: Gerard Blanchard <gblanchard@selu.edu> and
      Larry Lyons <larry@atmos.ucla.edu>

The final meeting of the Substorm Observations and Substorm Triggering
Working Groups of the Tail/Substorm Campaign contained discussions
summarizing the current status of topics of interest with the goal of
specifying "where we are today."  A synopsis of the proceedings follows.

A recap of the "substorm challenge" (Raeder) was presented in a
discussion of the state of MHD-based global modeling of the
magnetosphere during substorms.  The MHD-based global models
qualitatively reproduce a  remarkable number of substorm features,
however most comparisons were quantitatively off, and several important
issues were unresolved:  triggering, the  location and cause of the start
of expansion, timing within 2 minutes, effects of resistivity/diffusion,
and the role of the ionosphere.  Two speakers (McPherron, Blanchard)
addressed triggering of substorm onset by northward turnings of the IMF.
The consensus is that at least the majority of substorms are triggered.
Other speakers (Henderson, Lessard, Erickson) focused on specific auroral
features and their significance to the substorm onset mechanism:  torches
and omega bands, the location of  breakup relative to the Harang
discontinuity, the assertion that the breakup arc is stationary before
onset contrasted with the assertion that the breakup arc forms just
before onset.  These speakers asserted that M-I coupling plays a
significant role in the substorm onset mechanism.  There were several
presentations (Lyons, Mende, Donovan, Erickson) that discussed various
proposed substorm onset mechanisms.  These presentations generally
focused on the dynamics of the inner edge of the plasma sheet or of M-I
coupling.

The significance of these discussions for the GGCM is that while an MHD
backbone reproduces the gross features of a substorm well, the correct
modeling of substorms will require modules that include the proper
physics of the inner plasma sheet and of M-I coupling.

Finally, new observations were presented (Brandt, Jahn, Li) that may
play a role in future substorm research, such as CLUSTER II measurements
of plasma sheet thickness (as small as 0.2 RE) and ENA observations of
the plasma sheet, including such features as plasma sheet dropouts and
tracking of substorm injections.

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