Finally we briefly mention the IMF 
effect on the magnetic field and
particle populations at the site of POLAR.
The instrument called CEPPAD/IPS on board POLAR [ Blake et al., 1995]
observes ions in the energy range from 12 to 1500 keV. From 0000 to
0800 UT on March 28, 1996, this instrument observed almost nothing, except
for the interval from 0333 to 0357 UT when the instrument recorded
60 keV ions (not shown).
These ions were rich in He
and high-charge
state (>+6) Oxygen (not shown).
Thus they were of solar wind origin.
We note that IMF 
was negative during the interval from 0315 to
0420 UT (see Figure 1). Although IMF 
was negative
throughout the interval, reconnection at the lobe magnetopause is possible
due to the negative IMF 
, which could explain the observed solar
wind-origin particles.
at POLAR was generally increasing during this
interval (see Figure 2),
indicative of continuing dayside
merging. However, there was a small dip in 
around 0339 UT, which could be a diamagnetic effect caused by the particle
population.
We also note 
transiently decreased at the same
time, which
indicates that the magnetic field tilt briefly recovered toward the
pre-substorm value. Lobe reconnection at this time is consistent with
this change in the magnetic field tilt angle.