A model‐derived storm time asymmetric ring current driven electric field description

Abstract

[1] Low-latitude ionospheric and near-Earth magnetospheric electric fields are calculated from model results of the storm time asymmetric ring current. These fields are generated from subauroral field-aligned currents out of the ionosphere in the midnight sector and into the ionosphere on the dayside. The currents balance the divergence of the asymmetric ring current, which is the dominant component of the ring current during main phase and early recovery phase of magnetic storms. The basic shape of the electric potential pattern is described, both in the ionosphere and in the magnetosphere. It is found that intense ring current injection events can create potential differences up to 200 kV and can create local electric fields in the nightside magnetosphere >5 mV m À1 . The magnitudes and locations of the most intense electric fields are quite consistent with observations of subauroral (ionospheric) and near-Earth (magnetospheric) electric fields during magnetic storms. In addition, a relationship between the magnitude of the lowlatitude electric potential and the Dst* index is described. This relationship can be used to predict the location and size of strong low-latitude electric fields and currents. The presented electric field results are derived from model output, such that there is no feedback of the calculated fields back into the model.

Global observations of the zonal drift speed of equatorial ionospheric plasma bubbles

“…The drift speed is controlled by a downward, polarization electric field, which must be weakened or countered by an upward electric field to slow the drifts. This could originate in asymmetric separation of charges in the energized ring current, as recently described by Ridley and Liemohn (2002).…”

“…The zonal plasma drift speed variation observed here suggests that a radial electric field, possibly originating in the enhanced ring current, is present in the equatorial F-region. Such a source is described by Ridley and Liemohn (2002), where, in particular, the authors note the outward radial electric fields which develop on the nightside in response to enhancements in the region 2 current system occurring under magnetic storm conditions. Their simulation work predicts outward radial electric fields at ∼3000 km altitude of 2-10 mV/m during magnetic storms, with D st ranging from −50 to −200 nT.…”

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP

“…The RAM-SCB model can be driven either by empirical electric fields (e.g., Weimer 2001) and boundary conditions or by those provided from a global magnetohydrodynamics (MHD) model, e.g. BATSRUS (Powell et al 1999) selfconsistently coupled with an electric field model (RIM) (Ridley and Liemohn 2002) and driven by dynamic solar wind input. Figure 3 shows RAM-SCB simulations during the 22 April 2001 storm indicating significant depressions in the magnetic field intensity on the nightside during the storm main phase when the ring current pressure intensifies.…”

Model of electromagnetic ion cyclotron waves in the inner magnetosphere

“…The module dealing with the large-scale magnetosphere-ionosphere coupling and the model of the ionosphere used in our code have been developed at the University of Michigan [Liemohn et al, 2001;Ridley and Liemohn, 2002;Liemohn et al, 2004] [Lepping et al, 1995] and the Solar Wind Experiment [Ogilvie et al, 1995] instruments aboard the Wind satellite. The geomagnetic field in this study is taken to be a dipole field.…”