Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsm51a..01e&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM51A-01
Physics
2720 Energetic Particles: Trapped, 2730 Magnetosphere: Inner, 2736 Magnetosphere/Ionosphere Interactions (2431), 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)
Scientific paper
We will show how the ring current is profoundly influenced not only by the interplanetary magnetic field and the solar wind but also by the ionospheric conductivity, which is controlled by solar radiation and auroral electron precipitation. As a result of the accumulation of charged particles in the inner magnetosphere, an electric current flows perpendicularly to magnetic field lines (so-called the ring current). Field-aligned currents (FACs) flow when the divergence of the perpendicular electric current is nonzero. To remove the space charge deposited by the FACs, Pedersen currents are established in the ionosphere. The additional electric field distorts the convection electric field that is the prime driver for the ring current development. After performing a ring current simulation that self-consistently solves the kinetic equation of ring current protons and the closure of the electric current between the magnetosphere and ionosphere, we obtained the following results. (1) The conductivity for F10.7 = 250×104 Jy (solar maximum condition) is found to result in a ring current that is about 29 % stronger than for F10.7 = 70×104 Jy (solar minimum condition). (2) The conductivity at equinox results in a ring current that is about 5 % stronger than at solstice because the two- hemisphere height-integrated conductivities at equinox are higher than at solstice. This would be a new mechanism for explaining the semiannual variation of Dst. (3) The conductivity at 12 UT results in a ring current that is about 7-8 % stronger than at 00 UT. (4) Simulation with a realistic auroral conductivity estimated from the IMAGE/FUV auroral imager data reveals the fact that the overshielding condition is produced when the auroral conductivity decreases abruptly near the Dst minimum, triggering a rapid decay of the ring current. (5) The strength of the ring current is no longer proportional to the plasma sheet density because of an increase in the degree of the shielding with the plasma sheet density. The total energy of the ring current is found to be approximately proportional to square root of the plasma sheet density.
Ebihara Yasuhiro
Fok M.-
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