A new simulation model of upper atmospheric dynamics is presented that includes self‐consistent electrodynamic interactions between the thermosphere and ionosphere. This model, which we call the National Center for Atmospheric Research thermosphere‐ionosphere‐electrodynamic general circulation model (NCAR/TIE‐GCM), calculates the dynamo effects of thermospheric winds, and uses the resultant electric fields and currents in calculating the neutral and plasma dynamics. A realistic geomagnetic field geometry is used. Sample simulations for solar maximum equinox conditions illustrate two previously predicted effects of the feedback. Near the magnetic equator, the afternoon uplift of the ionosphere by an eastward electric field reduces ion drag on the neutral wind, so that relatively strong eastward winds can occur in the evening. In addition, a vertical electric field is generated by the low‐latitude wind, which produces east‐west plasma drifts in the same direction as the wind, further reducing the ion drag and resulting in stronger zonal winds.
We present a new technique for mapping high‐latitude electric fields and currents and their associated magnetic variations from sets of localized observational data. The technique generalizes earlier ones that were designed to deduce these electrodynamic features from ground‐based magnetometer data alone. In the new technique, many different types of measurements can potentially be used: electric fields from radars and satellites; electric currents from radars; and magnetic perturbations at the ground and at satellite heights. The technique also makes use of available statistical information about averages and variances of the electrodynamic fields. One of its advantages over earlier techniques is that it quantifies the errors inherent in the mapped fields, taking into account the distribution of available data, their errors, and the statistical variances of the fields. A related application of the procedure is used for estimating the distributions of high‐latitude ionospheric conductances, using available direct and indirect measurements. The new technique is illustrated by application to an example of a substorm that was previously analyzed by Kamide et al. (1982a) with an earlier technique. The new technique tends to yield much simpler patterns of high‐latitude ionospheric convection in regions of low ionospheric conductance. When magnetometer data alone are used, as in this example, the statistical uncertainty in the derived electric fields is largest in regions of low conductance, because the electric fields in these regions have little influence on the magnetic perturbations. A companion paper (Richmond et al., this issue) presents a detailed application of the technique using multiple data sets.
An approximate method of separating the effects of ionospheric currents from those of field‐aligned currents in ground magnetic perturbations observed in high latitudes is developed. The distribution of ionospheric electric fields can also be estimated. The procedure includes the following steps: (1) the calculation of the equivalent ionospheric current function on the basis of magnetic H and D component records on the earth's surface, (2) the computation of the electric potential distribution from the equivalent ionospheric current function by using a simple model of the ionospheric conductivity, (3) the derivation of ionospheric current vectors as well as electric fields and, (4) the derivation of the field‐aligned current intensity by taking the divergence of the ionospheric currents. Several examples for both quiet and disturbed conditions are utilized to demonstrate how our method is successful in estimating the intensities of the electric fields and the ionospheric and field‐aligned currents in the sense that the estimated values are in good agreement with those observed recently by radar and satellite methods. Significant portions of the H component in nightside auroral latitudes appear to result from the east‐west ionospheric currents, called the auroral electrojets, while both the north‐south ionospheric current and field‐aligned current are almost equally important in producing the D component excursions. It is found that the ionospheric and field‐aligned current distributions obtained are not very sensitive to the choice of the ionospheric conductivity model, unless the auroral enhancement is not given in an appropriate place. This indicates that even a simple conductivity distribution inferred from the distribution of the magnetic perturbations can make it possible to estimate the three‐dimensional current system with a reasonable accuracy.
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