This and the following two papers report results of the first comprehensive computer simulation of the behavior of the earth's inner magnetosphere during a substorm‐type event. Our computer model self‐consistently computes electric fields, currents, and plasma distributions and velocities in the inner‐magnetosphere/ionosphere system (L ≲10); parallel electric fields and ionospheric neutral winds are not included. In this paper, we derive the basic equations of the model, describe the inputs, and present an overview of results. The first appendix presents derivations of general, useful laws of bounce‐averaged gradient, curvature, and drifts in a plasma with isotropic pitch angle distributions. A second appendix describes the numerical method used in our computer simulation. The succeeding two papers present analyses of model results and comparisons with data. The model was applied to a substorm‐type event that occurred on September 19, 1976. Satellite data (primarily from the Air Force S3‐2 satellite) were used extensively both for boundary conditions and for comparisons with model predictions. Other data were also used as input for our time dependent magnetic field and conductivity models. The S3‐2 data for the event show some novel features, independent of the simulation. Dawn‐dusk electric fields show a general correlation with east‐west magnetic field perturbations. Unexpectedly, two of the passes display substantial regions of sunward plasma flow poleward of the main part of the region 1 Birkeland currents. The cross‐polar cap potential drops computed from the data represent the first effort at satellite monitoring of this important parameter during various phases of a substorm, and show an important enhancement during the substorm. Numerical results from these first‐try simulations are consistent with most of the established features of convection in the inner magnetosphere, such as generally sunward flow, shielding of the potential electric field for L <5, and the tendency for stronger electric fields on the duskside than on the dawnside. In addition, the model reproduces some typical substorm phenomena, such as energy‐dependent particle injection with a dawndusk asymmetry and establishment of a partial ring current.

Polar cap electric fields patterns are presented from times when the S3‐2 Satellite was near the dawn‐dusk meridian and IMF data were available. With Bz ≥ 0.7 γ, two characteristic types of electric field patterns were measured in the polar cap. In the sunlit polar cap the convection pattern usually consisted of four cells. Two of the cells were confined to the polar cap with sunward convection in the central portion of the cap. The other pair of cells were marked by anti‐sunward flow along the flanks of the polar cap and by sunward flow in the auroral oval. These observations are interpreted in terms of a model for magnetic merging at the poleward wall of the dayside polar cusp. The sunward flow in the auroral zone is not predicted by the magnetic model and may be due to a viscous interaction between the solar wind and magnetosphere. The second type, which was observed in some of the summer hemisphere passes and all of the winter ones, was characterized by an electric field pattern which was very turbulent, and may be related to inhomogeneous merging.

Electric and magnetic fields were measured by the CRRES spacecraft at an L‐value of 2.2 to 2.6 near 0300 magnetic local time during a strong storm sudden commencement (SSC) on March 24, 1991. The electric field signature at the spacecraft at the time of the SSC was characterized by a large amplitude oscillation (80 mV/m peak to peak) with a period corresponding to the 150 second drift echo period of the simultaneously observed 15 MeV electrons. Considerations of previous statistical studies of the magnitude of SSC electric and magnetic fields versus local time and analysis of the energization and cross‐L transport of the particles imply the existence of 200 to 300 mV/m electric fields over much of the dayside magnetosphere. These observations also suggest that the 15 MeV drift echo electrons were selectively energized because their gradient drift velocity allowed them to reside in the region of strong electric fields for the duration of the accelerating phase of the electric field.

No abstract

A dc electric field experiment on the Air Force satellite S3‐2 has occasionally detected intense localized electric fields near the ionosphere projection of the plasmapause. These poleward directed electric fields were observed in the pre‐midnight local time sector, seem to be related to substorm activity, and typically exceeded 100mV/m. In one case the field was 280mV/m corresponding to a drift velocity of 9.8 km/s at an altitude of 1463 km and a potential drop of 25 kilovolts. A possible source lies in the interaction between hot plasma freshly injected near magnetic midnight and the cold plasmaspheric particles. Since the potential drop is the order of the mean ring current energy, this structure may have important consequences for the understanding of magnetospheric flow patterns under disturbed conditions.