May 1998 has also been selected as a study event for the Second IACG Campaign on Boundaries in Collisionless Plasma ( see http://www-ssc.igpp.ucla.edu/IACG/May4_overview/index.html). The following description and links was copied from that site.
Overview of the Event
On May 4, 1998 the velocity and density of the solar wind were
high and the interplanetary magnetic field at times strong and
southward. The POLAR spacecraft crossed the dayside magnetopause
well inside geosynchronous orbit, at 5.3 RE and a solar zenith
angle of 19o. After this crossing, POLAR spent most of the rest
of its outbound orbit in the magnetosheath and for brief periods
crossed into the solar wind at distances from 7.3 RE and a solar
zenith angle of 32o to a distance of 8.5 RE and a solar zenith
angle of 45o. This corresponds to subsolar distances of only 6.8
to 7.5 RE for the shock. These observations are important not
solely because they are POLAR's only observations to date of the
subsolar magnetopause and the bow shock. The first magnetopause
crossing is a spectacular example of a rotational discontinuity
with a field change of 500 nT in the north-south direction with
no change in magnitude on either side of the current layer but
a depressed field strength within it. The normal component across
the current sheet is about 50 nT pointing inward as expected for
POLAR's northern hemisphere location. The six bow shock crossings
are all examples of supercritical shocks. The 3-axis electric
field experiment on board provides the opportunity to test assumptions
about the electric field across the bow shock for the first time.
Configuration of ISTP Spacecraft
On May 4 both WIND and ACE were close to the forward libration
point about 220 Re upstream. As shown in Figure
1 WIND was close to Earth-sun line as projected on the ecliptic
plane but about 27 RE above it as shown in the view from the sun
given in Figure
2. Thus both spacecraft should be of equal quality for providing
measurements of the input to the magnetosphere. The circles in
Figure
2 show the approximate radii of the magnetosphere for undisturbed
conditions and the most highly compressed conditions on this day.
In the neighborhood of the magnetopause Interball 1 was upstream of the average location of the bow shock as shown in Figure 3. Geotail and Imp 8 were in the region that would usually be the afternoon post dusk magnetosheath and Polar was in the dayside magnetosphere. The view from the sun in Figure 4 shows that Polar was crossing the dayside equatorial region moving to higher latitudes. Geotail was above the GSM equator and Interball 1 and Imp 8 significantly below the GSM equator.
Inside the magnetopause the GOES 8 and 9 spacecraft at synchronous orbit were on the nightside of the Earth during the most active period of activity as shown in Figure 5.
