Post-Midnight Enhancements in the Storm Time Ring Current

Fok, M., Moore, T.E., Wolf, R.A., Spiro, R.W., Sazykin, S., C:son Brandt, P. 


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. The local times of the maximum flux seem to vary with IMF By and solar wind
velocity. 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. This paper will explore the physical
processes that control this local-time asymmetry. We seek to understand how these
mechanisms control the effects of solar wind, convection, and ionospheric conductances on
observed ring current local-time distribution. 
		   
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Fall 2002 Meeting of the American Geophysical Union
San Francisco, CA, USA, 6-10 December 2002