Modelling Inner Magnetospheric Electric Fields: Latest Self-Consistent Results

Stanislav Sazykin (Physics and Astronomy Dept., Rice University, Houston, TX), 
Robert W. Spiro, Richard A. Wolf, Nikolai A. Tsyganenko


This paper presents the latest results of self-consistent numerical modeling of
large-scale inner-magnetospheric electric fields obtained with the Rice
Convection Model (RCM). The model reasonably well describes the well-understood
phenomenology of inner magnetospheric electrodynamics. Inner magnetospheric
convection, driven ultimately by the interaction of the solar wind with Earth's
magnetosphere, sets up a system of field-aligned (region-2) currents via
pressure gradients. These field-aligned (Birkeland) currents close in the
ionosphere by means of horizontal currents driven by ionospheric electric
fields, which act to exert feedback control over particle flows in the plasma
sheet inner edge and ring current regions. The RCM treats plasma drifts,
electric fields, and currents in the inner magnetosphere self-consistently in
the quasi-static (slow-flow) approximation under the assumption that the
pitch-angle distribution is isotropic.

Recently, the details of the electric field and plasma pressure distributions
near the equatorward edge of the diffuse aurora during strong magnetic storms
have attracted intense attention as a result of new ground-based and spacecraft
observations and newly emerging magnetospheric imaging techniques. Results of
event simulations of the magnetic storms of March 31, 2001 and April 17, 2002
will be used to investigate three topics of current interest:

(1) The local-time location of the peak ion flux in the storm main-phase ring
current. Though conventional ring current models typically place this peak near
local dusk, ENA images indicate that the main-phase ring current often peaks
significantly later, near midnight or even in the post-midnight sector. The
physical relationship between the peak of the ring current and SubAuroral
Polarization Stream (SAPS) events, which have recently been defined as regions
of extended westward plasma flow equatorward of the nightside auroral zone, will
be discussed, and both will be shown to depend strongly on features of the
ionospheric conductance.

(2) The effect of severe distortion of the magnetic field during very large
magnetic storms. Results will show how use of a new empirical storm-time
magnetospheric magnetic field model affects computed electric field and particle
pressure distributions.

(3) Solar-wind driving of the plasma sheet. It has been shown that the
temperature and the density of the plasma sheet population, a major source of
the storm-time ring current, is directly correlated with solar wind parameters.
Results of simulations with plasma boundary sources varying in response to
measured solar wind inputs will be compared with those of simulations where the
plasma boundary sources were kept constant.

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Presented at the August 2003 AGU Chapman Conference, Helsinki, Finland