Working Group 2 Report:  GEM Snowmass Meeting June 1995

     Throughout the GEM Boundary Layer Campaign there has been
steady progress in understanding the magnetospheric boundary layers and
this year was no exception.  In the past most progress was made with
observations at high altitudes, near the equatorial plane and near the nose
of the magnetosphere.  Here it became clear that reconnection was the
dominant physical mechanism both when the IMF was southward and
when it was northward.  The evidence for this was multifold.  There was
no evidence for diffusion being important since the plasma boundaries
remained sharp.  Boundary layers appeared to be rather uniform in
properties as if the entire layer was a mixture of similar starting plasmas
and the boundary layers contained the occasion impulsive injection with
field aligned flows.  This year additional work on this problem by Guan
Le suggested that when the IMF was strongly northward the LLBL
consisted of two regions: one on open field lines of most recently
reconnected field connected to the Earth at one end and one on closed
field lines that had undergone reconnection at high latitudes in both the
north and the south tail lobes.
     The interpretations of the low altitude data are similarly as difficult
as at high altitudes. Pat Newell expalined clearly how these observations
could be explained using the semi-quantitative model of Terry Onsager.
interpretation in a tutorial presentation.  This was followed by a detailed
examination of this mechanism and its consequences by Mike Lockwood. 
While there is still more to be understood, there is more agreement in the
boundary layer community than there ever has been in the past.  While it
is presumptuous to claim that this accord was solely the result of the GEM
workshops, it is true that the denouement of this new understanding took
place at the GEM meetings.
     There was much new to be learned in addition to the resolution of
old controversies.  The GEOTAIL mission was just completing its third
year of operation in the equatorial region and despite its optimization for
tail studies has proven itself to be a powerful probe of processes at the
dayside magnetopause.  The latest data on the GEOTAIL studies at the
magnetopause and in the low latitude boundary layer were reported by M.
Nakamura and M. Fujimoto.  In November 1994 after a series of
unfortunate delays, the WIND spacecraft was finally launched into an
orbit almost the mirror image of that of GEOTAIL.  Where GEOTAIL
skimmed the magnetopause and goes far down the tail, WIND passes
through the near tail region and goes deep into the solar wind.  While not
optimized for magnetospheric studies, the instruments on the WIND
spacecraft still are a powerful advance over the instruments of the late
70's and early 80's on which most of our present understanding is based. 
Preliminary results of low latitude electrons by T. Onsager, on energetic
magnetosheath particles by R. Skaug, and on energetic particle
composition measurements by H. Paquette.  All results were very
intriguing but clearly not yet at the stage of sophisticated analysis that
allows the testing of models.
     The magnetosphere has boundary layers outside the current layer
as well as inside. The magnetized plasma of the magnetosheath has to be
deflected around the obstacle so that both the plasma and the magnetic
field are carried around the obstacle and this process must obey the laws
of physics for which MHD is usually a good approximation.  MHD tells
us that there are three waves, each of which has an othogonal role to play
in the interaction.  Under most circumstances the slowest mode is the
wave that compresses the density and rarefies the magnetic field or vice
versa (in an expansion fan).  This mode is generally referred to as the
slow mode.  The mode should stand in front of the magnetopause where
the normal component of the magnetosheath flow matches the slow mode
velocity.  Controversy has arisen in the past both over the existence and
the proper physical explanation for such structures.  Paul Song has been
the main advocate of the standing slow mode wave.  Lou Lee's group
have in turn presented an alternate explanation in terms of transient
phenomena.  This year was no exception.  Paul Song presented improved
evidence for the phenomenon through the comparison of observations with
space forecaster's models.  This presentation, thus, made use of two of
the present thrusts of the GEM campaign; the comparison of in situ data
with theory; and the use of space forecast models to predict
magnetospheric behavior.  The space forecast models, as expected, did not
exhibit the variations seen in the observations as they were only
gasdynamic in nature but they clearly proved the phenomenon was spatial
and not temporal in nature.  The opposite viewpoint was presented by M.
Yan and Y. Lin who discussed models of the interaction of rotational
discontinuities with the bow shock and the generation of pressure pulses
in the magnetosheath.
     The remaining presentations engendered far less controversy. 
There were discussions of time varying reconnection and flux transfer
events by Lockwood, the location of magnetopause reconnection by
Onsager, magnetic reconnection by A. Otto, H. Cai and J. Drake, wave
interaction with the magnetopause current layer by J. Johnson and the low
latitude boundary layer by C-Q Wei.  Overall there was much more to be
discussed than there was time to do so but nevertheless much was
accomplished.