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.

We present preliminary results of a magnetospheric substorm that occurred on applying the Rice convection model to the early September 19, 1976 [Harel et al., 1981a,b; Spiro main phase of the magnetic storm of July 29, et al., 1981; Karty et al., 1982; Chen et al., 1977. The computer model self-consistently com-1982]. The relationship of the Rice convection putes electric fields and currents, as well as model to other related theoretical formulations, plasma distributions and velocities, in the and our model's basis in earlier research, were inner-magnetosphere/ionosphere system. In the described in Harel et al. [1981a]. For the sake 1present address is Mail Code 144-218, Jet Pro-B. Formulation

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Results of the Rice University substormn simulation have been used to investigate the penetration of substorm-associated electric fields into the plasmasphere. Near 4 RE) in the equatorial plane, our time-dependent electric field model is characterized by eastward components in the dusk-midnight local time sector and westward components after midnight. Except for a small region Just before dusk the model predicts eastward electric field components throughout the daytime sector. The characteristic radial component is directed-\-inward at all local times except for a small region just after dawn. These results compare favorably with available whistler and incoherent scatter measurements obtainid during magnetically disturbed periods.By assUmingan initial plasmapause shape and by following the computed E x B drift trajectories of plasma flux tubes from that initial boundary we have examined the short-term evolution of the plasmapause during the substorm-like event of 19 September 1976. We find that narrow filamentary tails can be drawn out from the plasmasphere near dusk within hours of substorm onset. These tail-like appendages to the plasmasphere subsequently drift rapidly from the dusk sector toward the daytime magnetopause.Investigation of the large-scale time-dependent flow of plasma in the evening sector indicates that some mid-latitude plasma flux tubes that drift eastward past the dusk terminator reverse their motion between dusk and midnight and begin to drift westward toward dusk. Such time-dependent changes in flow trajectories may be related to the formation of F-region ionization troughs. " ' tea.Unclassified -

Several results of the computer simulation of the behavior of the inner magnetosphere during the substorm‐type event of September 19, 1976, are discussed in detail. The model predicts a modest ring current injection, in to L ≈ 6, with total strength that is comparable to the strength estimated from the observed decrease in Dst. For the geosynchronous orbit region on the duskside, the model predicts a characteristic energy dispersion often observed by McIlwain and collaborators: energetic ions arrive first after substorm onset, followed by less energetic ions. The computed electric fields compare satisfactorily with electric fields measured from S3‐2, although there are detailed differences. Three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high‐latitude electric field, (2) the degree to which the low‐latitude ionosphere is shielded from the high‐latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. The observations indicated one instance of rapid flow equatorward of the auroral zone, involving an electric field of more than 100 mV/m. This rapid subauroral flow was accurately predicted by the model. The predicted east‐west magnetic perturbations due to region 2 Birkeland currents agree satisfactorily with S3‐2 observations with regard to direction, total magnitude, and general location, but there is an important general discrepancy: in most cases, the actual Birkeland currents were distributed over a wider range of latitude than the model would predict. Speculations are presented as to possible explanations of the discrepancy. The model Birkeland currents agree satisfactorily with the averaged observations of Iijima and Potemra, in terms of direction, strength, and overall pattern. The model suggests a theoretical interpretation of the observed overlap region near midnight, where a region of upward Birkeland current is bounded on its equatorward and poleward sides by regions of downward current. The model provides a useful picture of the overall magnetosphere‐ionosphere current system. It also suggests that the observed asymmetry in the change of the horizontal magnetic field at low‐latitude ground stations during the main phase of a magnetic storm should not be interpreted simply as asymmetric development of the inner‐magnetospheric ring current and the associated region 2 Birkeland currents. Region 1 Birkeland currents, which connect to the outer magnetosphere, play a major role in the asymmetry of low‐latitude ΔH, while overhead Hall currents seem to play a lesser role. The model indicates that the total Joule heating during the event is approximately three times the increase in ring current energy, a result that is in apparent contradiction to some previous estimates. A general, but highly approximate, analytic argument is presented in support of this result of the simulation. Some simple formulas ...

The Rice convection model (RCM) is utilized to investigate the electrodynamic coupling between the inner magnetosphere and the thermosphere including the effects of EUV‐ and convection‐driven neutral winds under quasi‐equilibrium conditions. It is shown that the parameters determining the coupling are the Pedersen and Hall “effective winds”, which are the height integrals of the respective conductivity‐weighted wind profiles divided by the respective layer conductivities. Their appearance in the RCM is equivalent to a two‐slab formulation whereby the integrated Hall conductivity originates in the lower slab, the integrated Pedersen conductivity originates in the upper slab, and the height dependence of the neutral wind is accounted for by assuming different wind vectors for the lower and upper slab. A unique aspect of the study is that the convection‐driven winds are included self‐consistently and interactively; that is, a steady state wind parameterization is written analytically in terms of the electrostatic potential, which is in turn included in a closed‐loop calculation for the electric potential itself. Simulations are performed from 1400 UT to 1600 UT during the CDAW‐6 interval on March 22, 1979, when the cross‐cap electric potential attains values of order 140–180 kV. During the early phases of the disturbance when the normal shielding from high latitudes breaks down, the neutral winds do not modify appreciably the disturbance electric fields at middle and low latitudes. As the system approaches a quasi‐equilibrium state, the neutral winds play a much more significant role. By comparison with the “no‐wind” simulation, the fields driven by EUV winds counteract the fields of magnetospheric origin and give the appearance of a shielding effect. The convection driven component of the neutral wind similarly acts to reduce the southward field in the noon sector, but gives rise to an enhancement in the dusk sector field extending to middle latitudes. The parameterized Pedersen effective winds are of order 300 ms−1 and reflect the familiar two‐cell pattern with antisunward flow over the polar cap and return flows in the dawn and dusk sectors. These amplitudes and similarity with the ion drift motions reflect the relatively large contribution to the Pedersen effective winds originating in the upper E region and lower F region of the ionosphere. Possibilities for introducing further sophistication into the wind parameterization are discussed, as well as ramifications of the present study on the possible merging of the RCM with the NCAR TGCM to attain a higher degree of self‐consistency and reality in modelling efforts.

Using substorm currents derived from the Rice computer simulation of the substorm event of September 19, 1976, we have computed theoretical magnetograms as a function of universal time for various stations. A theoretical Dst has also been computed. Our computed magnetograms were obtained by integrating the Biot‐Savart law over a maze of approximately 2700 wires and bands that carry the ring currents, the Birkeland currents, and the horizontal ionospheric currents. Ground currents and dynamo currents were neglected. Computed contributions to the magnetic field perturbation from eleven different kinds of currents are displayed (e.g., ring currents, northern hemisphere Birkeland currents). On the basis of comparison of theoretical results with corresponding observations, we make the following remarks. First, overall agreement of theory and data is generally satisfactory, especially for stations at high and mid‐magnetic latitudes. Second, model results suggest that the ground magnetic field perturbations arise from very complicated combinations of different kinds of currents and that the magnetic field disturbances due to different but related currents often cancel each other, despite the fact that complicated inhomogeneous conductivities in our model prevent rigorous application of Fukushima's theorem. Third, both the theoretical and observed Dst decrease during the expansion phase of the substorm, but data indicate that Dst relaxes back toward its initial value within about an hour after the peak of the substorm. This effect exists qualitatively in the computer simulation if we sharply reduce the assumed polar cap potential drop and conductivity at the end of the substorm. Fourth, the dawn‐dusk asymmetry in the horizontal component of magnetic field disturbance at low latitudes in a substorm is essentially due to a net downward Birkeland current at noon, net upward current at midnight, and generally antisunward flowing electrojets; it is not due to a physical partial ring current injected into the duskside of the inner magnetosphere.