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REPORT ON 1993 SNOWMASS WORKSHOP 
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             GEM WORKING GROUP 3: CURRENT SYSTEMS AND MAPPINGS
                Co-chairs: C. T. Russell and R. L. Lysak

     This year Working Group 3 experimented with discussing only 
one topic but studying it in depth.  The topic chosen was Traveling 
Convection Vortices (TCV) also called Traveling Ionospheric Vortices 
(TIV) and Magnetic Impulse Events (MIE).  These events are of significant
interest to the members of the working group because they are isolated 
events which seem amenable to attack.  They provide a clear example of 
magnetosphere-ionosphere coupling, and they provide an opportunity for 
theorists and observationalists to work jointly.  The events are 
significant perturbers of the ionosphere where and when they occur.  They 
are not observed throughout most of the magnetosphere, only in the dayside 
auroral oval.  Evidence for particle acceleration has been found as well 
as optical emissions in conjunction with these events.

     TCVs were originally thought to be the ionospheric manifestation of 
the magnetopause phenomenon known as a flux transfer event (FTE).  TCVs 
seem to be a little larger than FTEs projected into the ionosphere up to 
400 km for FTEs versus up to 1000 km for TCVs.  However, since TCVs are 
rare (once every 3 days at a particular station on average) this difference 
could reflect the fact that only the largest TCVs are detected.  Multiple 
FTEs are often found in a sequence, but TCVs are usually isolated.  This 
isolation may be a selection affect.  M. McHenry who looked for multiple 
TCV events, found them.  The major difference between TCVs and FTEs is that 
FTEs are almost exclusively a southward IMF effect.

     The properties of TCVs are somewhat sensitive to the selection criteria 
and different groups use different criteria.  Most criteria used tend to be 
conservative so that small TCVs can be missed.  TCVs appear to be only one 
phenomenon of several causing fluctuations in the auroral ionosphere, but 
TCVs can be characterized more easily.  Sometimes TCVs arise out of a quiet 
background.  At times TCVs appear to be caused by some process entering a 
non-linear state.

     A new discovery is that their lifetime is short.  TCVs decay in a time 
not much longer than their duration.  Hence, they do not travel far.  For 
small TCVs (200-400 km) it is difficult to see how they can be found only at 
noon and then be seen everywhere throughout the dayside oval if they decay 
this rapidly.  Otherwise, the properties are consistent with a noon local 
time source.  The events generally (but not always) move away from noon and 
there are seldom any events seen at noon.  There is a tilt to the pattern 
seen in north-south arrays that is consistent with the travel time of waves 
generated at the boundary.  There is also a dawn/dusk asymmetry with most 
TCVs seen in the dawn sector.  However, this asymmetry appears to be 
sensitive to selection criteria because McHenry, who examined multiple 
element TCVs, found more on the afternoon side.

     In an extensive study of magnetic impulse events at a single station, 
Igaluit (formerly Frobisher Bay), Lou Lanzerotti found that dynamic pressure 
played an important role in only 15-30% of the cases but that reconnection 
is important in 50-90% of the events.  Also, the size of the Bx and By 
components of the IMF seem to have some controlling effect on the events. 
The north-south field seems to have less effect but fluctuations in the 
field seem to be important.

     The working group noted that the work on TCVs thus far had been mainly 
with magnetometers and that in future studies using unlocated remote sensing 
instruments such as optical, x-ray and riometer measurements would be useful.
Preliminary data from the scanning riometer seemed particularly promising.

     The working group plans to follow up on these deliberations at the GEM 
mini-workshops at the AGU meeting in San Francisco.  Next year we plan to 
examine in detail one or more new topics.  One possible topic is the 
large-scale field aligned current systems of the magnetosphere and their 
control by solar wind conditions.  Suggestions and comments on our future 
activities are solicited.