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Reports of Boundary Layer Campaign Working Groups Meetings
Snowmass, Colorado, June 28-30, 1992
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      Report of GEM Working Group 3:  Current Systems and Mapping 
              R. L. Lysak and C. T. Russell (co-chairs)

    Working Group 3 at the Snowmass Workshop consisted of a group of about
20 scientists interested in currents, waves and mapping issues.  The group
concentrated on three main issues during this workshop:  traveling 
convection vortices, ULF waves, and sources and mapping of dayside 
currents.  Each of these topics was introduced by a keynote speaker, who 
gave a short review of the field followed by a lively discussion by the 
participants.
    The subject of traveling convection vortices was introduced by Eigil
Friis-Christensen, who gave an extensive review of the properties and 
problems involved in observing and interpreting these events. The 
consensus view was that these vortices are related to dynamic pressure 
pulses, although a number of participants emphasized that the 
interplanetary magnetic field (IMF) seemed to play an important role in 
these events.  An apparent dawn/dusk asymmetry in the occurrence of these 
events has been found, although statistics by various groups show a 
different degree of asymmetry, making its interpretation a little difficult.  
It was noted that these events were prime candidates for study by the 
extensive magnetometer array covering nearly half the auroral oval which 
will be available when the MACCS array of Jeff Hughes and Mark Engebretson 
is completed to complement magnetometer arrays in Greenland, at lower 
latitudes in Canada, and in Alaska.
    ULF waves in the range from a few minutes to a few seconds were also
extensively discussed, with the discussion being introduced by Mark
Engebretson.  A primary subject of emphasis in this area was the prospect
of using wave data as a ground-based tracer of the ionospheric footprint 
of various region of the cusp and dayside magnetopause. Brian Fraser 
pointed out that pulsations in the Pc1-2 band (roughly 1-10 second 
periods) provide a very good tracer of the cusp and dayside boundary layer
regions.  Engebretson also discussed issues related to the propagation of 
compressional and transverse ULF waves in the dayside magnetosphere, 
questioning the traditional view of mode conversion due to field line 
resonances with some new ideas of mode coupling through modulations in the
ionospheric conductivity.
    Mike Lockwood reviewed source mechanisms for dayside field-aligned
currents, contrasting currents occurring on clearly open field lines in 
the cusp with the Region I currents occurring further away from noon which
may be on open or closed field lines. Effects such as viscosity, parallel
electric fields and ionospheric conductivity gradients can lead to 
field-aligned currents in regions other than the open/closed field line 
boundary, and it was recognized in the discussion that the open/closed 
boundary was not always in the same place as boundaries in the visible or
UV aurora, convection reversal boundaries, or field-aligned current 
boundaries.  Joel Fedder showed some results from an MHD simulation with 
directly northward IMF which showed that region I currents could occur in 
a nearly totally closed magnetosphere, which were driven not by viscosity
but rather by a time-dependent reconnection at the cusps.  In this area, 
there were certainly more questions raised than any clear answers to the 
current generation problem.