Simulated Stormtime Ring-Current Magnetic Field Produced by Ions and Electrons

Using drift-loss simulations, we investigate the stormtime ring-current magnetic field produced by protons and electrons during the 19 October 1998 storm. We compute the guiding-center drift motion of equatorially-mirroring protons and electrons in a model magnetosphere and consider H charge exchange loss and electron precipitation due to pitch-angle scattering. We simulate perpendicular particle pressure distributions and the ring-current magnetic field in the equatorial plane. Our quiet-time proton ring current model reproduces a radial perpendicular pressure profile that is similar to statistical observations. Both the proton and electron ring current form asymmetrically early in the storm main phase and become stronger and more nearly symmetric later in the main phase. We find that the quiettime electron ring-current magnetic field is negligible compared to the quiet-time proton ring-current magnetic field. However, during storms, electrons contribute ~ 15-20% of protons to the total Dst. Thus, the electrons contribute significantly to the total ring current during storms. There are large asymmetric stormtime ringcurrent magnetic field depressions at r₀ ~ 3.5-6 R_E. The simulated large magnetic field depressions agree qualitatively with statistical observations. These magnetic field depressions are a significant fraction of the geomagnetic field, indicating a need for a magnetically self-consistent treatment of the particle transport. The large ring-current magnetic depressions should be included in global descriptions of the inner magnetosphere.