Magnetically Self-Consistent Simulations of Ring Current for the 19 October 1998 Storm

Details Magnetically Self-Consistent Simulations of Ring Current for the 19 October 1998 Storm Magnetically Self-Consistent Simulations of Ring Current for the 19 October 1998 Storm

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsa13b..07c&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SA13B-07

Statistics

Computation

2720 Energetic Particles: Trapped, 2730 Magnetosphere: Inner, 2753 Numerical Modeling, 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)

Scientific paper

We investigate effects of magnetic self-consistency on ring-current development for the 19 October 1998 storm by calculating equatorial particle transport in a model that feeds back effects of the ring current on the magnetospheric configuration. As in our past work, we treat magnetic field lines as contours of constant L and Φ, satisfying the equation r = La [1 + 0.5(r/b)3] sin2θ, where r is the distance from the point dipole, a is the radius of Earth, and θ is the co-latitude measured from Earth's dipole axis. We allow b to vary with Φ and with L so as to simulate the magnetic effects of a mostly azimuthal ring current. The values of b, which control how much each field line is stretched relative to a dipole field, are determined from the equatorial magnetic intensity B_0. Here we assume for simplicity that each magnetic field line always lies in the same meridional plane (i.e., that there is no bending-back or twisting of field lines). The equatorial magnetic intensity B_0 is computed by solving a force-balance equation in the equatorial plane. This force-balance computation is coupled to a kinetic drift-loss model for ring-current protons and electrons, a model similar to that used in our previous work. The simplified electric-field model used for this study includes corotation, quiescent Volland-Stern convection, and storm-associated enhancements in the convection electric field. 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 enhancements in the Volland-Stern potential drop across the polar cap of our model B field. Upon comparing simulation results with and without magnetic self-consistency, we have found overall that magnetic self-consistency reduces the simulated equatorial perpendicular plasma pressure by a factor ~2 to 3. Self-consistent feedback between plasma pressure and the magnetic field thus tends to mitigate the energization associated with inward particle transport as the ring current forms. However, we find that the self-consistent magnetic field reduces the azimuthal E x B drift rate even as it significantly enhances the azimuthal gradient-B drift rate. We have found, especially later in the main phase, that there can be places where the plasma pressure and magnetic perturbation are locally enhanced by making the simulation magnetically self-consistent. This usually occurs because of enhanced drift rates in regions of reduced magnetic intensity.

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