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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, A08205, doi:10.1029/2003JA010351, 2004

Influence of ionosphere conductivity on the ring current

Y. Ebihara

Universities Space Research Association, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


M.-C. Fok

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


R. A. Wolf

Rice University, Houston, Texas, USA


T. J. Immel

University of California, Berkeley, California, USA


T. E. Moore

NASA Goddard Space Flight Center, Greenbelt, Maryland, USA


Abstract

Using the Comprehensive Ring Current Model (CRCM), which self-consistently solves the kinetic equation of ring current protons and the closure of the electric current between the magnetosphere and ionosphere, we have studied how different changes in the ionospheric conductivity affect the strength of the ring current. The conductivity for F10.7 = 250 × 104 Janskys (Jy) (solar maximum condition) results in a ring current that is about 29% stronger than for F10.7 = 70 × 104 Jy (solar minimum condition). 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. Simulation with a realistic auroral conductivity estimated from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE)/Far Ultraviolet Imager (FUV) auroral imager data reveals the fact that auroral brightenings do not significantly change the intensity of the ring current. The overshielding condition is found to be produced when the auroral conductivity decreases abruptly near the Dst minimum, triggering a rapid decay of the ring current. The ring current is shown to be influenced not only by the interplanetary magnetic field and the solar wind but also by solar radiation and morphological features of the auroral electron precipitation as well.

Received 6 December 2003; accepted 29 April 2004; published 28 August 2004.

Keywords: magnetic storms; ring current; ionosphere conductivity; sheilding; Dst index; numerical simulation.

Index Terms: 2778 Magnetospheric Physics: Ring current; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2730 Magnetospheric Physics: Magnetosphere—inner; 2720 Magnetospheric Physics: Energetic particles, trapped.

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Citation: Ebihara, Y., M.-C. Fok, R. A. Wolf, T. J. Immel, and T. E. Moore (2004), Influence of ionosphere conductivity on the ring current, J. Geophys. Res., 109, A08205, doi:10.1029/2003JA010351.