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			 **   THE GEM MESSENGER   **
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						     Volume 5, Number 8
						     March 23, 1995

			
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Mini-GEM Workshop Report, December 4, 1994, San Francisco - Part III
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MAGNETOTAIL/SUBSTORM CAMPAIGN WG2: SUBSTORM/TAIL PHENOMONOLOGY:
				   OBSERVATIONS AND MODELS

Working Group 2 met on the Sunday prior to the Fall AGU meeting to
discuss magnetotail/substorm phenomenology and to explore possible
model/data comparisons.  The three topics that received the majority
of the discussion were:  (1) Where does the arc associated with the
break-up phase of substorms map in the magnetotail, and can an
empirical, time-dependent magnetic field model be constructed to
investigate this question, (2) Where do field-aligned currents map,
and (3) What further observational constraints can we put on the
causes of dipolarization?  On this final point, Lou Lee presented
calculations suggesting that dipolarization may be caused by a steep
entropy gradient that exists prior to substorm onset.  As might
be expected, no consensus was reached on these topics.

The next task for Working Group 2 is to identify specific questions
and model predictions that can be compared with available data.   As
mentioned above, one example of this would be the construction of
an empirical, time-dependent magnetic field model to investigate
the location of the break-up arc.  Nikolai Tsyganenko mentioned that
his current modeling efforts could perhaps be extended to address
this question.  Another example is the integration of a plasma sheet
and a plasma sheet boundary layer model by Harlan Spence and
Terry Onsager that can be compared with low-altitude particle
measurements.  We are particularly interested in identifying
other examples where specific comparisons can be made between the
predictions of various models within the GEM community and the
available data.  Working Group 1 has compiled an extensive set of
coordinated data, including ground-based, near-Earth, and deep-tail
measurements that should allow for quantitative tests of various
magnetotail models.  We would like to solicit requests from those in
the GEM community who are interested in testing their model calculations
with the available data.  We can then assist in acquiring the data
and in coordinating with similar comparisons being conducted by others.
These comparisons will then be discussed at the summer GEM meeting.

Co-chairs:
Terry Onsager:  onsager at gus.unh.edu
Harlan Spence:  spence at bu.edu

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