Magnetically self-consistent ring current simulations during the 19 October 1998 storm

We investigate effects of magnetic self-consistency on ring current development by calculating equatorial particle transport in a model that feeds back the ring current on the magnetospheric configuration. The equatorial magnetic intensity is computed by solving a force-balance equation in the equatorial plane. This force-balance computation is coupled to a kinetic proton and electron drift-loss model. The electric field model used includes corotation, quiescent Volland-Stern convection, and storm-associated enhancements in the convection. We have modeled the 19 October 1998 storm (min Dst = -112 nT) by using the total cross polar cap potential from AMIE to determine the amplitudes of storm-associated electric field enhancements. We trace equatorially mirroring protons and electrons within this model. We have found that self-consistent feedback between plasma pressure and the magnetic field tends to mitigate the energization associated with inward particle transport as the ring current forms. At a given first adiabatic invariant and radial distance, the self-consistent magnetic field reduces the E x B drift rate as it significantly enhances the azimuthal gradient-B drift rate. Especially later in the main phase, there can be places where the plasma pressure and magnetic perturbation are locally enhanced by making the simulation magnetically self-consistent because of enhanced drift rates in regions of reduced magnetic intensity. The southward magnetic perturbation at the center of the Earth, which represents the ring current contribution to the Dst index, is reduced by about 25% by making the simulation magnetically self-consistent. This suggests that simulations that do not take account of the feedback of the ring current overestimate the actual ring current intensity.