Ring Current Modeling in the Global Geospace

Mei-Ching Fok, NASA GSFC


Earth's ring current is a large-scale electrical current system
encircling the magnetic equator at typical radial distances of 2 to 8
earth radii.  The current is carried principally by westward drifting
trapped ions originated from the solar wind and the ionosphere.
Additional partial ring currents also flow part way around the Earth
in the middle magnetosphere.  Field aligned currents connect the ends
of the partial rings to the ionosphere, where the currents can
complete the circuit. In the traditional picture of development of
the storm-time ring current,  most of the ions that are injected on
the night side gradient-curvature drift westward around the Earth,
causing the main-phase ring current to peak near local dusk.  In
contrast, previous simulations carried out with the Rice Convection
Model (RCM), typically showed a ring current with a maximum near
midnight.  Recent neutral atom images of the ring current from
IMAGE/HENA reveal strong enhancements in the post-midnight sector
during storm main phases, even further from the traditional picture.
Simulations carried out with the Comprehensive Ring Current Model,
which couples the RCM and Fok's ring current model, showed remarkably
good agreement with the IMAGE/HENA data.  Preliminary analysis shows
that magnetosphere-ionosphere coupling plays an important role in the
formation of these post-midnight enhancements.  In this talk, we will
explore the physical processes that control this local-time
asymmetry.  Finally, we will also discuss the coupling of ring
current model with global MHD models.

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Space and Cosmic Ray Physics Seminar, University of Maryland
4:30 p.m., 30 September 2002