Magnetospheric Current System During Disturbed Times

1
Magnetospheric Current System During Disturbed
Times
2
October 19, 1998 Storm
Proton Pressure Using Bounce-Averaged Particle
Drift Simulations
Magnetic Field Perturbation
0500 UT
Pre-storm
1130 UT
Magnetohydrodynamic Pressure 0800 UT
1130 UT
0500 UT
3
Pressure and Temperature From Guiding Center
Particles 0300 to 0600 UT
4

• The 18-19 October 1998 storm (minimum Dst 125
  nT) was selected as a study event. We applied
  global MHD simulation, particle trajectory
  calculations and ring current simulations to this
  event.
• Particle Drift Simulations
• Trace bounce-averaged drifts of ions that
  conserve the first two adiabatic invariants M and
  J.
• Dipole and uniform southward magnetic field were
  assumed in this model
• AMIE electric potentials were mapped analytically
  from ionosphere to anywhere in magnetic field
  model.
• Guiding center
• A distribution of particle at energies above 5
  keV are launched on the night side at r 10 RE
  within 21º of the x axis. At 0300 and 0400 UT
  600,000 particles were launched.
• Trace the guiding center drifts of ions that
  conserve the first adiabatic invariant M in the
  MHD electric and magnetic fields .

5

• MHD Inner Magnetosphere
• The MHD simulation shows a pressure increase at
  the beginning of the main phase that is located
  on the dusk side.
• In general, however, the MHD simulation had a
  relatively low pressure in the inner
  magnetosphere during the storm (maximum about 2
  nPa).
• Guiding Center Particles in MHD Fields
• The pressure due to the test particles was
  greater in the inner magnetosphere during the
  storm than the MHD model (maximum about 10 nPa).
• Substantial particle losses occur through the
  dusk side (tail and dayside) and on open field
  lines in the cusp region. Most of the particles
  that were launched formed a partial ring current
  on the dusk side.
• Particle Drift Simulations
• The ring current simulation showed greater
  pressures in the inner magnetosphere (the highest
  pressure about 30 nPa) than either the MHD or the
  guiding center particle simulations.
• At later times the particle drift simulations
  ring current became more symmetric and very
  intense.

6

• Model Comparisons
• Guiding center particle calculations led pressure
  maxima greater than the MHD result but less than
  the particle drift model. The particles were
  strongly energized by the electric fields but
  substantial losses at the (mainly dusk side)
  magnetopause and near the cusp reduced the
  pressure due to these particles.
• The particle drift simulation showed the highest
  pressure but did not include loss mechanisms that
  were important in the guiding center particle
  calculations.
• To complete this study we will
• Investigate the dynamics of the inner
  magnetosphere by self-consistently combining a
  particle-based ring current model with a global
  MHD model.
• Include particle pressure in the MHD momentum
  equation to account for the particle drift.