The Magnetosphere‐Thermosphere‐Ionosphere‐Electrodynamics General Circulation model of Peymirat et al. [1998] is used to investigate ionospheric‐wind‐dynamo influences on low‐latitude ionospheric electric fields during and after a magnetic storm. Simulations are performed with time‐varying polar cap electric potentials and an expanding and contracting polar cap boundary. Three influences on equatorial electric fields can be of comparable importance: (1) global winds driven by solar heating; (2) direct penetration of polar cap electric fields to the equator that are partially shielded by the effects of Region‐2 field‐aligned currents; and (3) disturbance winds driven by high‐latitude heating and ion‐drag acceleration. The first two influences tend to have similar magnetic local time (MLT) variations in a steady state, while the disturbance‐wind influence tends to have the opposite MLT variations. The nighttime disturbance winds at upper midlatitudes that affect the global ionospheric wind dynamo are predominantly westward after the simulated magnetic storm. The nighttime winds drive an equatorward dynamo current that tends to charge the low‐latitude ionosphere positively around midnight, which can lead to reductions or reversals of the normal equatorial night‐side east‐west electric fields. The simulations partly support the theories of the so‐called “disturbance dynamo” [Blanc and Richmond, 1980] and “fossil wind” [Spiro et al., 1988], both of which predict long‐lasting disturbances in the equatorial eastward electric field associated with magnetic storms. However, the simulations do not support the element of fossil wind theory that links the disturbance‐wind influence on equatorial electric fields to polar cap contraction following the storm. The simulations show a stronger wind‐produced enhancement of steady state shielding than predicted by the model of Forbes and Harel [1989], due to the fact that the disturbance winds extend well equatorward of the Region‐2 currents.

Abstract.The penetration of the electric field and associated magnetic perturbations from high latitudes to low latitudes is studied with the Magnetosphere-Thermosphere- Ionosphere-Electrodynamics General

Abstract. The penetration of disturbance electric fields from the polar region to the magnetic equator on the dayside of the Earth is examined with geomagnetic data on May 27, 1993. First, we examine a dayside equatorial disturbance that followed the rapid recovery of magnetic activity from a storm and that has the characteristics of overshielding caused by persistent region-2 field-aligned currents.

Early results of a new self‐consistent fluid model are presented for steady convection of the plasma from the geomagnetic tail through the Earth's inner magnetosphere below 10 Earth radii (RE), including its coupling with the ionosphere. This model computes the transport of both the ion and electron fluids and constitutes an important improvement of the fluid numerical model of Fontaine et al. (1985) (referred to as Paper 1), which simulated the convection of electrons only. The coupling with the ionospheric convection is effected by the precipitation of magnetospheric electrons, which enhances ionospheric auroral conductivities, and by the flow of region 2 field‐aligned currents, which connect the magnetospheric and ionospheric circuits. This last coupling was not considered in Paper 1, because region 2 field‐aligned currents are generated mainly by pressure gradients of the ion plasma that develop progressively during its motion. We also take into account the ion precipitation, which affects the generation of region 2 field‐aligned currents, but we neglect their relatively small effect on the ionospheric conductivities. We devoted much effort to produce a self‐consistent description of the transport of the ionospheric and magnetospheric plasmas, and their couplings. As a first step, in order to distinguish basic physical processes from effects of geometrical origin, we solved the equations for the case of a dipolar magnetic field as in Paper 1. As a consequence, we do not expect our results to reproduce very precisely the available observations but rather to provide only correct orders of magnitude. The numerical solution scheme of the hyperbolic equations governing the transport of both magnetospheric ions and electrons, of the elliptic equation of the ionospheric electrostatic potential, and of their coupling due to electron precipitation and region 2 field‐aligned currents, is basically the same as Paper 1. It makes use of the finite element method. The numerical model is run to simulate the evolution of the system from an initial state in which the inner magnetosphere is free of plasma, to a steady state situation in which the plasma has penetrated into the inner magnetosphere from the tail. Stable magnetic conditions corresponding to a Kp between 2 and 3 are considered to allow a comparison with observations. The formation of a belt of electron and ion precipitation in the auroral zone is globally reproduced by the model, but the electron fluxes are underestimated and the auroral ion zone is located equatorward with regard to the DMSP satellite statistical observations. The field‐aligned current region 2 computed by the model is comparable to the available statistical observations, apart from an underestimation of the amplitude. The convection structure is also found comparable to observations, thus improving the results of Paper 1. The amplitude and the direction of the major component of the electric field (the northward component being at least 4 times larger than the eastward component) is consistent w...

Abstract. A new simulation model of the thermosphere, the ionosphere, and the magnetosphere is presented. This model, which we call the magnetospherethermosphere-ionosphere electrodynamics general circulation model (MTIE-GCM), calculates the three-dimensional structure of the thermosphere and the ionosphere, the two-dimensional magnetospheric plasma convection in the equatorial plane of the magnetosphere, and the couplings among the thermosphere, the ionosphere, and the •nagnetosphere. The electrodynamic couplings induced by the auroral precipitation, the region 2 field-aligned currents, and the neutral winds are selfconsistently computed. The major drawback of the model is the use of a dipole magnetic field in the magnetosphere such that we do not expect to reproduce observations exactly but rather to predict only correct orders of magnitude. The MTIE-GCM is run for solar maximum conditions and moderate magnetic activity in a sample case, where the electric potential is imposed in the polar cap but calculated everywhere else, to study the electrodynamic couplings occurring at high latitudes. The neutral winds increase the north-south component and decrease the east-west component of the ionospheric electric field, corresponding to an enhancement of the shielding effect by 10%. The region 2 field-aligned currents and the distribution of the magnetospheric pressure present smaller modifications, suggesting that the magnetosphere acts partly as a current generator. However, the results could possibly be different if the polar cap electric potential were allowed to change due to the neutral winds.