An empirical model of thermospheric temperature (T∞T120, and s) and composition (H, He, N, O, N2, O2, and Ar) was derived from measurements of 8 satellites (AE-C, AE-E, AEROS-A, AEROS-B, ARIEL-3, ESRO-4, OGO-6, and SAN MARCO-3) and 4 incoherent scatter stations (Arecibo, Jicamarca, Millstone Hill, and St Santin). The altitude covered extends from 120 km up to about 600 km over the time period 1967 to 1976. The analytical framework used in the model resembles closely the MSIS setup: time independent terms, solar flux terms, geomagnetic activity (Kp) effect, annual (semiannual) and diurnal (semidiurnal, terdiurnal) variations, longitudinal terms, the U.T. effect, and corrections compensating for deviations from diffusive equilibrium at altitudes below 200 km. The model describes quiet to medium disturbed geomagnetic conditions (Kp ≲ 4) at solar fluxes (10.7cm) ranging from 60 to 180 × 10−22 Wm−2Hz−1. To get an impression of the accuracy presently obtained, the model is compared with MSIS, Jacchia (1977), and the models of Thuillier (T∞ and Engebretson (N). The best agreement is found for the temperature and the constituents He, O, and N2 with increasing deviations in the order of H, N, Ar, and O2.

An analysis of several global measures of high‐latitude ionospheric electrodynamic activity is undertaken on the basis of results obtained from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure applied to incoherent scatter radar and ground magnetometer observations for January 18–19, 1984. Different global measures of electric potentials, currents, resistances, and energy transfer from the magnetosphere show temporal variations that are generally well correlated. We present parameterizations of these quantities in terms of the AE index and the hemispheric power index of precipitating auroral particles. It is shown how error estimates of the mapped electric fields can be used to correct the estimation of Joule heating. Global measures of potential drop, field‐aligned current, and Joule heating as obtained by the AMIE procedure are compared with similar measures presented in previous studies. Agreement is found to within the uncertainties inherent in each study. The mean potential drop through which field‐aligned currents flow in closing through the ionosphere is approximately 28% of the total polar cap potential drop under all conditions during these 2 days. We note that order‐of‐magnitude differences can appear when comparing different global measures of total electric current flow and of effective resistances of the global circuit, so that care must be exercised in choosing characteristic values of these parameters for circuit‐analogy studies of ionosphere‐magnetosphere electrodynamic coupling.

The ionosphere and the magnetosphere are coupled by three basic processes: transmission of electric fields, exchange of electric charges (field-aligned currents), and exchange of particles (by precipitation and/or outflow). All the three processes essentially operate along the same field lines, and are intimately connected in such a complicated way that for many purposes their description and understanding requires numerical simulation. Ionosphere-magnetosphere coupling operates at different temporal and spatial scales, and each different scale domain is part of a different problem and needs to be described by a different approach.

The large‐scale electric potential patterns, describing ionospheric convection, are estimated for northern high latitudes during January 18‐19, 1984, from combined incoherent‐scatter radar and ground magnetometer observations, using the technique of Richmond and Kamide (this issue). The patterns usually have a dominant two‐cell characteristic, although the intensities, orientations and shapes of the cells undergo considerable changes with time. Often evident during substorm expansive phases is a “tongue” of low electric potential extending toward the east along the low‐latitude edge of the high potential cell at night. Time‐series plots of the maximum and minimum electric potentials show that they can respond rapidly to changes in the interplanetary magnetic field Bz component. Total estimated potential drops for this 2‐day period range from about 15 kV up to 108 kV. The influence of the different types of data on the resultant estimated electric potential patterns is analyzed. Where available, the direct electric field observations by the radars primarily control the characteristics of the estimated potential patterns, while the magnetometer data have their greatest influence in regions where direct electric field measurements are unavailable. We also employ the statistical electric potential model of Foster et al. (1986) to help fill in the patterns in datasparse regions. For the present study, data coverage is often good enough that the statistical model plays only a secondary role in determining the estimated convection patterns. The ionospheric electrical conductance observations from the Sondrestrom and EISCAT radars are very important in helping modify the statistical conductance model of Fuller‐Rowell and Evans (1987) to yield modified conductance distributions suitable for interrelating the electric fields, currents, and magnetic perturbations. Analysis of the statistical uncertainty in the estimated large‐scale electric field patterns shows the uncertainty to exceed 50% in the polar cap and sub auroral regions and to be less than 20% only in the vicinity of the radar electric field observations.

This tract is primarily devoted to the numerical simulation of physical phenomena occurring in both the magnetosphere and the ionosphere of the earth. Finite elements and a method of characteristics are combined to simulate numerically the complex interactions between particles emitted by the sun and the various electromagnetic fields surrounding the earth. The computed results agree well with observations obtained from satellite measurements. 57 references.

We present a new self‐consistent model of the transport of hot electrons in the earth's magnetosphere and of their precipitation in the auroral ionosphere. In this model, the electron transport is described by the same fluid equations as in the work by Fontaine and Blanc (1983). But the electric field distribution which drives electron motions is computed from the equations of ionospheric currents, instead of being described by an empirical model as previously. The two basic equations to be solved, the hyperbolic equation governing electron transport and the elliptic equation governing the ionosphere current flow and the distribution of the electrostatic potential on the ionospheric conductor, are coupled via the ionospheric conductivities, which are functions of the electron precipitation flux at the top of the ionosphere. The numerical model is run to simulate the evolution of the system from an initial state in which there is no hot electron in the inner magnetosphere, to a steady state situation in which electrons penetrate into the inner magnetosphere from the tail and are transported onward until they precipitate into the ionosphere. To achieve this, the dawn‐to‐dusk electrostatic potential drop which is induced by the solar wind across the magnetosphere is turned on at t = 0 and maintained constant for the rest of the simulation. Using different values of this potential drop for each individual run, we simulate various levels of magnetic activity and compare our results with observations. The formation of a belt of electron precipitation in the auroral zones is very well reproduced by the model. Both its distribution in local time and the ionospheric location of its equatorward edge agree fairly well with statistical models derived from satellite observations of the auroral electron precipitation zones. On this latter point the agreement with observations is improved relative to our previous study. The formation of the electron precipitation belt modifies the convection pattern as it generates a localized enhancement of ionospheric conductivities in the auroral zone. This modification is essentially negligible on the sunlit side of the earth, where convection remains controlled by the distribution of conductivities due to the solar illumination. But it is very sensitive on the nightside, where the equipotentials are strongly distorted at the poleward and equatorward edges of the belt of enhanced conductivities, and where the evening vortex expands toward middle latitudes. In the equatorial plane of the magnetosphere, the shape of the plasmapause is also well reproduced; but its absolute size is underestimated for high levels of magnetic activity. A careful comparison of our computed electric fields with the fields measured at auroral and middle latitudes by several ionospheric incoherent scatter radars indicates that the shape of the local time variation of the fields is reproduced reasonably well, given the uncertainties inherent to the statistical averages derived from observations, and the intrinsic variability of the geophysical context. However, there is some indication that our model underestimates the magnitude of the meridional electric field at high latitudes, overestimates it at mid‐latitudes, and predicts a position in local time of the convection vortices which is two or three hours westward of the observed ones. These discrepancies can receive the same explanation: the lack of a trapped population of energetic ions in our model, which other studies have shown to be responsible for increasing the high‐latitude electric field and decreasing appreciably the mid‐latitude electric field. Our next step in magnetospheric convection modeling will be to develop a two‐fluid theory in which both electron and ion transport equations will be self‐consistently coupled to the equation of the ionospheric electrical circuit.

Between May 1981 and June 1982 an intensive campaign of 33 coordinated observations was carried out using the three incoherent‐scatter radars capable of probing the auroral zone. During this period the groups operating the Dynamic Explorer satellites and the STARE radar made special efforts to acquire data coincident with the radar observations. The objective of these MITHRAS experiments and subsequent analysis is to further our understanding of the interactions of the magnetosphere, the ionosphere, and the thermosphere, with special emphasis on local time/universal time variations. Three experimental modes with different time resolution and spatial coverage were used to examine different aspects of these interactions. The analysis of the extensive data set involves collaboration among groups of experimenters as well as between experimenters and theoreticians.

A self‐consistent semianalytical model of magnetospheric convection including the effect of the latitude and local time variations of ionospheric conductivities is presented. The motions of the inner edge of the magnetospheric ring current, and the associated field‐aligned currents, produced by the externally imposed dawn‐to‐dusk potential drop across the magnetospheric cavity are computed by using a linear approximation. The coupling between the different diurnal harmonics in the local time variations of fields and currents produced by the local time dependence of ionospheric conductivities is described by an appropriate matrix formalism. The calculations show that the enhancement of auroral conductivities by electron precipitation in the auroral zone significantly enhances both the typical duration and the absolute amplitude of the penetration of convection electric fields to midlatitudes. Furthermore, the local time variations of the convection electric field generated at midlatitudes by a sudden increase of the dawn‐to‐dusk potential drop are in good agreement, both at the initial time and after the steady state is reached, with the available statistical models of the disturbance midlatitude electric field. The amplitude of the steady state field seems sufficient to explain these observations, thus confirming that the concept of the shielding of midlatitudes from the convection electric fields is basically correct but was overestimated in earlier analytical calculations. The large subauroral electric fields observed by several satellites are also reproduced in the model either by a decrease of the subauroral conductivities below the midlatitude values or by the consideration of a very narrow latitudinal extent of the auroral zone. The overall consistency between the results of the model and the electric field observations thus supports the idea that a large class of phenomena related to magnetospheric convection in the dipole regions of the magnetosphere can be described in a reasonably realistic manner by a linear theory.

The interrelationship of equatorial and planetary scale ionospheric horizontal currents on quiet days is studied by means of a global ionospheric wind dynamo simulation. This simulation aims at reproducing magnetic and radar data first for a normal quiet day, and then for the strong counterelectrojet event of January 21, 1977, which was previously studied in detail on the basis of coherent backscatter radar data for the

The interrelationship of equatorial and planetary scale ionospheric horizontal currents on quiet days is studied by means of a global ionospheric wind dynamo simulation. This simulation aims at reproducing magnetic and radar data first for a normal quiet day, and then for the strong counterelectrojet event of January 21, 1977, which was previously studied in detail on the basis of coherent backscatter radar data for the Addis‐Ababa location. For the reference quiet day (January 27, 1977), the pattern of low and middle latitude currents and electric fields can be roughly reproduced by a combination of the (1,−2) and (2,2) solar tides. Both the Sq current system, and the global electrostatic potential distribution as derived by Richmond et al. [1980] from incoherent scatter data are well simulated. Direct comparison of the computed electric field with the quiet‐day averages available for each radar site also show an excellent agreement on the east‐west component, but a poorer one on the north‐south component. The counterelectrojet simulation is performed by fitting the H component trace at the magnetic equator and the D trace at midlatitudes. The result appears to give a consistent solution to the problem of the electrical connection between the equatorial counterelectrojet and the planetary dynamo layer. Two horizontal current vortices of opposite directions are found to flow at low latitudes on each side of the noon sector, anticlockwise in the morning and clockwise in the afternoon. They both produce a poleward current flow at low latitudes at noon, a feature that is detected on the magnetic records. The counterelectrojet event is reproduced by a combination of the (2,2) and (2,4) solar tides, assuming that the contribution of the diurnal tide to the altitude‐integrated current flow cancels out. This result is in agreement with a previous simulation study of the counterelectrojet phenomenon.

A theoretical investigation of the generating mechanisms of the disturbance E×B drifts observed at mid‐latitudes is performed, with the purpose of understanding the local time dependence of the average disturbance drifts observed above Saint‐Santin (L = 1.8, 47° geomagnetic latitude) and of extending if to other latitudes. To this end, the middle‐ and low‐latitude effects of the two possible generators of electric field disturbances, the solar wind/magnetosphere dynamo, and the ionospheric wind disturbance dynamo, computed by means of a numerical dynamo model of the ionosphere, are systematically compared with the Saint‐Santin disturbance drift pattern. The solar wind/magnetosphere dynamo is simulated as an electrostatic potential generator at 75° latitude, and its local time dependence determined by least squares fitting the drifts calculated at 45° latitude to the observed drift pattern. When the solar wind/magnetosphere dynamo only is considered, the best fit is found for a diurnal sinusoīdal shape of the 75° latitude potential corresponding to a 40 kV total potential drop across the polar cap rotated by 2 hours eastwards from the dawn‐dusk direction. But this source reproduces only one half of the 34‐m/s westward steady component observed in Saint‐Santin average disturbance drifts. The remaining gap can be filled by inclusion of Blanc and Richmond's (1980) disturbance dynamo electric field model into the fitting procedure. This fitting procedure provides a global theoretical pattern of disturbance electric fields and E×B drifts within the plasmasphere that can be compared with observations. Three latitude zones can be distinguished in the resulting picture. In the external regions of the plasmasphere, one finds an extension of the usual picture of high‐latitude plasma drifts, eastward in the morning and westward in the afternoon. The calculated drifts compare fairly well with the drifts disturbance models produced from whistler data at L = 4 and from the Millstone Hill radar. At mid‐latitudes, between 55° and 20° invariant latitude, we predict that the superposition of the two dynamos produces westward drifts at all local times; this is consistent with the Saint‐Santin and Arecibo radar drift data.

We analyze simultaneous measurements by the incoherent scatter radars at Saint‐Santin (45° latitude) and Chatanika (65° latitude) during a major magnetic storm in April 1978 to examine several disturbance mechanisms operating on the mid‐latitude ionosphere during periods of strong magnetospheric and auroral activity. The first type of mechanism, the extension of magnetospheric convection electric fields to mid‐latitudes, is illustrated by two large localized departures of the E×B plasma drifts over Saint‐Santin that appeared in conjunction with the two storm negative phases. In both cases they were associated with large electric fields in the afternoon sector, within the eastward electrojet region, over Chatanika. The first event can be very clearly interpreted as a global short term enhancement of magnetospheric convection electric fields, since simultaneous plasma flux intensifications were identified over the polar cap, in the afternoon eastward electrojet, and at 45° latitude. The IMF and ring current signatures of these two events confirm our previous findings: large southward values of BƵ and large values of the rate of energy injection into the ring current system, are associated with the extension of magnetospheric convection electric fields to midlatitudes. In addition, a marked equatorward shift of the auroral oval was observed during both events. During the night of the first event, the mid‐latitude drift perturbation magnitudes remained moderate (100 m/s) and did not seem to induce any significant ionospheric perturbation. The joint increase in ion and electron temperatures by 100 to 200° K above the quiet day reference level, which preserved the thermal equilibrium of the plasma, can be simply interpreted in terms of the storm‐induced global heating of the thermospheric gas. Conversely, on the night of the second event, when drift magnitudes reached several hundreds of m/s, large‐amplitude fluctuations in the F layer height and density, and very large increases (by more than 500° K) in the ion and electron temperatures were observed. Whereas collisional heating can account for a large part of the ion temperature increase, an additional energy source, heating preferentially the electron gas, is needed to explain the maintenance of the electron temperature 200° K above the ion temperature observed from the onset of the Dst decrease onward during that night. The identification of this source suffers from the lack of additional data, in particular photometric ones, in the Saint‐Santin sector. However, the unusually large fields observed at Saint‐Santin and the equatorward shift of the auroral zone observed at Chatanika in the early afternoon suggest that the plasmapause may have moved close to Saint‐Santin and that the enhanced electron temperatures observed there might have been produced by a SAR arc.

We use Ohm's law and a combination of various local models of the electrodynamic parameters of the ionsphere derived from previous incoherent scatter studies (electric fields, neutral winds, ion composition, and ion neutral collision frequencies) to generate an empirical model of the local time and seasonal variations of the horizontal electric current flow above Saint‐Santin (geographic latitude 44.1°N, geographic longitude 2.3°E). The various contributions to the total current (Hall and Pedersen contributions, neutral wind driven contributions, and electric field driven contributions) are explicitly obtained in this model. The local time variations of the two components of the total height‐integrated horizontal current are compared with the Sr magnetic variation at our location. For all seasons the zonal component is weak, mainly as the result of equal and opposite contributions of the electric field and neutral winds. This result, which is consistent with the weak observed Sr variation of H, is expected for a station such as ours close to the latitude of the Sq focus where the current flow is essentially meridional. In contrast to the usual picture of the Sq system, which suggests a southward current in the morning and a northward current in the afternoon, our model meridional current is found to be always northward during the daytime. This surprising feature of the model is supported by the direct calculation of the current from the ion drifts on a series of individual days. Examination of the SR variation of the D component of ground magnetic variations shows that a north‐south current asymmetry, though of smaller intensity, is also present in the magnetic variations. Both the net northward flow of charges revealed by the ionospheric data, and the observed discrepancy between calculated ionospheric currents and magnetic data, suggest that field‐aligned currents must be flowing from the northern to the southern hemisphere in our longitude sector during a least part of the day. This situation seems to be quite different from the American sector, where no similar asymmetry has been detected in the average current flow over Millstone Hill. Explanations of these features will have to involve the possible effects of the inclination of the magnetic dipole of the earth with respect to its rotation axis, as well as of antisymmetric tidal modes, which are likely to produce, interhemispheric asymmetries and longitude variations.

This paper presents an introduction to a global campaign of simultaneous quasistatic electric field measurements from radars, balloons, and satellites at various places within the earth's environment for April 8–14, 1978. The 7‐day time period encompassed both extended magnetically quiet times as well as two magnetic storms. These storms were related to SSC's that followed solar flares, one of which included a day‐long solar proton event. The wide variety of instrumentation and associated operating modes involved in this campaign is described. Sample conjunctions between satellites and ionospheric measurements are shown that demonstrate that field line mapping is valid under certrain circumstances. Some of the largest ionospheric electric fields ever reported with >100‐km scale size occurred on April 11, and these events are discussed in detail.

We analyze three‐dimensional ion drift data from the Saint‐Santin incoherent scatter facility to test experimentally the theoretical description of ion transport in the ionospheric dynamo layer, and to deduce electric fields and ion neutral collision frequencies from the observed drifts. Using a geometrical representation of the ion momentum equation, we show that at middle latitudes, because horizontal neutral wind influences ion motions both parallel and orthogonal to the field lines in the ionospheric dynamo layer, the information contained in a three‐dimensional ion drift measurement is redundant, thus permitting to check the standard theoretical description of ionospheric electrodynamics in two ways. First, assuming a model ion‐neutral collision frequency profile, one can deduce the north‐south perpendicular component of the electric field function of height in the E region from Saint‐Santin drift data. We find that its altitude variations remain within the experimental uncertainty of the method, in agreement with the theoretical assumption of equipotential field lines. Second, assuming that the electric field is constant in altitude, one can determine the ion collision ratio, or ratio of the ion collision frequency to the ion gyrofrequency, from a comparison of E and F region drift measurements. Daily median values of the ion collision frequencies, thus obtained for each of the three seasons, are found to compare reasonably well with ion collision frequencies derived from the Jacchia neutral atmosphere model for the case of the equinox sample, but determinations for the other seasons are contaminated by a high level of measurement noise.

Seasonally averaged quiet‐day F region ionospheric E × B drift observations from the Millstone Hill, St. Santin, Arecibo, and Jicamarca incoherent scatter radars are used to produce a model of the middle and low‐latitude electric field for solar minimum conditions. A function similar to an electrostatic potential is fitted to the data to provide model values continuous in latitude, longitude, time of day, and day of the year. This model is intended to serve as a reference standard for applications requiring global knowledge of the mean electric field or requiring information at some location removed from the observing radars. This article contains supplementary material.

A seasonal model of the F region electric‐field‐induced plasma drifts prevailing during magnetically quiet periods, and of their day‐to‐day variability, has been established on the basis of 3 years of measurements (1973–1975) above Saint‐Santin (44°39′N, 2° 12′E) with the French quadristatic incoherent scatter facility. It is expressed analytically with the help of a steady component and of the first four diurnal harmonic oscillations and can be used both as a base line for magnetospheric disturbance studies and in itself as a source of information on the morphology of ionospheric wind dynamo electric fields. For all seasons these drifts appear to be dominated by a semidiurnal oscillation in the north‐south direction and by a diurnal one in the east‐west direction. During the daytime the flow is northwestward in the morning and then southeastward in the afternoon. Seasonal effects are dominated by a marked contrast between summer and the two other seasons. Summer is characterized by a disappearance of the morning northward drifts and a more complex harmonic content of the east‐west drifts, with a larger contribution of the secondary semidiurnal and terdiurnal components. Comparison with recent dynamo calculations shows an improved agreement on the north‐south component of the drifts, even though it still leaves a significant gap between theory and experiment. Several elements in our results provide evidence that the attempt to realize a good theory/experiment coincidence meets several difficulties of a fundamental nature: one is the lack of a simple summer/winter symmetry in the observed drifts, which reveals the importance of longitude effects introduced by the real earth's magnetic field; another is the large day‐to‐day variability within each season, which is comparable to the diurnal amplitude itself. Both show the need of worldwide coordinated efforts for the acquisition of simultaneous incoherent scatter data as well as for their interpretation.

The extension of magnetospheric convection toward low latitudes is investigated with the help of incoherent scatter measurements of E×B plasma drift velocities in the midlatitude F region above Saint‐Santin (France). The observed relations of these drifts with auroral magnetic activity, the north‐south component Bz of the interplanetary magnetic field, and the time derivative of Dst suggest that this low‐latitude extension is not systematically associated with all polar magnetic substorms, but occurs in conjunction with large (5 gammas or more) southward Bz and is closely related in intensity with the negative excursions of d(Dst)/dt. We propose that plasma injection and the resulting development of an asymmetric ring current are closely linked with the low‐latitude extension of magnetospheric convection.

The Saint-Santin facility has been operating in its quadristatic configuration since October 1973. A set of 8 days and 7 nights (winter and equinox) of F region drift measurements perpendicular to the magnetic field is presented and provides information on the ionospheric electric fields. For quiet magnetic conditions the day-to-day variability is found to be weak, and the corresponding daily variations show the dominance of a 50 m/s diurnal oscillation in east-west drifts and of a 15–20 m/s terdiurnal oscillation in north-south drifts. None of the presently available models of quiet time electric fields have been found to reproduce this data over 24 hours. Comparison with other mid- and low-latitude electric field results shows a rather good agreement with incoherent scatter results south of Saint-Santin but a strong contrast with Millstone Hill results despite comparable geographic latitudes. For disturbed magnetic conditions, perpendicular drift velocities appear displaced from their quiet day values with a tendency to westward deviations. On some occasions those displacements reach large values of 100 m/s (4 mV/m electric field) and more over 1 or 2 hours. An interpretation in terms of penetration of the plasmasphere by electric fields associated with magnetospheric substorms is suggested.