Jan 10, 1997

1
MHD model and data comparisons
April 30, 1998
Jan 10, 1997
2
Comparisons of the Raeder MHD model results with
data from the DMSP spacecraft and the Polar UVI
auroral imager for two solar wind dynamic
pressure eventsThe vertical line indicates the
time of high pressure impact on the
magnetosphere.We focus our comparison on the
motion of the separatrix boundary, the area of
open flux, and the cross polar cap potential
(CPCP)

• For the Jan 10, 1997 event
• The pressure pulse occurred while no other solar
  wind or IMF property varies. IMF is strongly
  southward.
• The AU and AL indices indicate no substorm
  activity
• Both the model and the UVI indicate closure of
  the polar cap (reduction of the open flux area)
  at the same time
• Both the model and DMSP indicate a significant
  increase of convection (increase of CPCP) at the
  same time
• The increase of the cross polar cap potential
  while the polar cap closes is a counter-intuitive
  result, that is observed for southward IMF
  conditions.

• For the April 30, 1998 event
• Large step pressure increase occurs while the IMF
  is relatively steady and near zero.
• No UVI data available and the model does not show
  closure of the polar cap. DMSP (not shown)
  indicates only some polar cap closure
• Both the model and DMSP show show significant
  increase in the CPCP at the same time.
• The response of convection and the area of open
  flux to pressure enhancements is strongly
  dependent on IMF conditions. Comparisons between
  the MHD model and observations will help us
  understand the physical causes of these responses.