Numerical Simulation of the Ring Current: Review |
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Authors: | Ebihara Yusuke Ejiri Masaki |
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Institution: | (1) National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo 173-8515, Japan |
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Abstract: | Numerical simulation of the terrestrial ring current is reviewed. After mentioning ‘modules’ which are needed to be taken
into consideration in a ring current simulation, we discuss growth and decay of the ring current. At least four different
paradigms have been proposed to account for the ring current development in the past forty years, i.e., the convection paradigm, the substorm paradigm, the diffusion paradigm, and the ionosphere paradigm. As for the proton ring
current, a simulation under the convection paradigm gives reasonable results which are in fair agreement with observations
with respect to the Dst variation as well as the radial and longitudinal energy density variation of protons when the convection
electric field depending on solar wind parameters is given. The proton energy density is observed to be enhanced (weakened)
on the nightside, and be weakened (enhanced) near noon during a storm main phase (recovery phase). This characteristic is
probably understood to mean that a large-scale and long-standing electric field dominates other electric fields during the
storm main phase, e.g., a locally induced electric field (the substorm paradigm) and a highly fluctuated electric field (the diffusion paradigm).
The declining of the ring current is shown to be triggered by the decrease in the convection electric field at the beginning
of a storm recovery phase, but the decrease in the convection electric field hardly contributes the decay of the ring current.
The charge exchange or other loss processes is needed for the substantial decay of it. An ultimate decay rate (several hours)
is achieved when the strong diffusion takes place, or when the plasma sheet density drastically decreases while the charge
exchange is estimated to provide rather slow decay (a half of day). Diagnosis tools for investigating the ring current, which
are expected to bring us a new insight, are proposed in the latter section.
This revised version was published online in June 2006 with corrections to the Cover Date. |
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