indices. Our present estimates give t•e following relationshi•s: Uj • 2.3 times 10 v ß AE, U A • 0.6 times 10 8 ß AE and U I = 2.9 times 108 ß AE; Uj -3.0 times 108 ß AL U -0.8 times 108 ß AL, and U I -3.8 times 10 • -AAL. Injection Rate

We analyze ionospheric convection pat terns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assirnilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF By and B, components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (

Abstract. An attempt is made to construct an improved ionospheric conductance model employing ground magnetic disturbance data as input. For each of the different regions in the auroral electrojets specified by different combinations of horizontal ( It is proposed that the present conductance model can be used to complement more direct measurements in order to obtain the global distribution needed to study the large-scale electrodynamics of the polar ionosphere. Several interesting characteristics about the auroral electrojet system are apparent from the empirical relationship: (1) For a given magnitude of AH, the electric field is relatively stronger in the eastward electrojet region than in the westward electrojet region. (2) The electric field plays a greater role in the intensification of electrojet current than the ionospheric conductance does in the poleward half of the westward electrojet, whereas the opposite trend is apparent in the equatorward half. However, no such different roles of the electric field and conductance is noticeable in the eastward electrojet region. (3) The auroral conductance enhancements tend to be largest around midnight, due to more intense particle fluxes there. (4) The mean particle energy depends on MLT but is relatively insensitive to magnetic activity.

Abstract. Using the hourly mean AE indices for the past 20 years, amounting to a total of 175,296 hours, we examine how the longitudinal station gaps of the present AE network affect the ability to monitor accurately the auroral electrojets. The latitudinal shift of the auroral electrojet location with magnetic activity also affects the reliability of the AE indices. These combined effects would result in pronounced universal time (UT) variations of the AE indices. By counting the number of occurrences recorded during the given ranges of activity, say every 100 and 200 nT for the A U and AL indices, respectively, for each hour of universal time, the UT variations of the two indices are examined separately. The result demonstrates clearly that they are strongly dependent upon UT. Furthermore, it is noted that the equatorward expansion of the auroral electrojets is more responsible for the UT variation than are the longitudinal station gaps. For the range of the magnetic activity levels examined in this study, i.e., 0 to 500 nT and 0 to -1000 nT for the A U and AL indices, the centers of the eastward and westward electrojets seem to be located within the latitudinal ranges of 71ø-65 ø and 680-62 ø , respectively. The seasonal change of ionospheric conductance also contributes to the UT variation, particularly that of the AL index. While maintaining a similar variation pattern, the amplitude of the variation increases during winter and decreases during summer. It indicates that the UT variation of the AL index is more serious during winter than summer. With more AE stations being located within the former range than the latter, it is easily understood why the AL index is more strongly dependent on UT than is the A U index. Considering such a latitudinal distribution, it is highly probable that the present AL indices often underestimate disturbed conditions during specific universal time intervals, particularly 0200-0800 UT.

As a part of the joint efforts of operating six meridian chains of magnetometers during the IMS, magnetic records from 70 stations are used to deduce patterns of electric fields and currents in high latitudes on March 17, 18, and 19, 1978. First of all this data set is used to examine the fidelity of the AE(12) index by comparing it with the AE(70) index and also the fidelity of the AL(70) index as a measure of the total westward electrojet intensity. The coefficients for the two correlations are found to be more than 0.8. Then the distribution of both ionospheric currents and field‐aligned currents, as well as the electric field, are for the first time determined with a time resolution of 5 min by using an appropriate conductivity distribution model. Although much improvement is still needed for better accuracy, especially in the estimation of ionospheric conductivity, it has now become possible to study the growth and decay of the three‐dimensional current system over the north polar region during individual magnetospheric substorms with sufficient time resolution. Our initial results show that the gross features of the instantaneous distributions of the ionospheric and field‐aligned currents are remarkably similar to the daily average pattern during a very weak activity and at different substorm epochs and that the large‐scale current pattern grows and decays systematically as a whole. There are, however, significant changes in local scales.

The instantaneous patterns of electric fields and currents in the high‐latitude ionosphere are deduced by combining satellite and radar measurements of the ionospheric drift velocity, along with ground‐based magnetometer observations for October 25, 1981. For this purpose, an updated version of the assimilative mapping of ionospheric electrodynamics technique has been used. These global patterns are unobtainable from any single data set. The period under study was characterized by a relatively stable southward interplanetary magnetic field (IMF), so that the obtained electric field patterns do reflect, in general, the state of sustained and enhanced plasma convection in the magnetosphere. During one of the satellite passes, however, an intense westward electrojet caused by a substorm intruded into the satellite (DE 2) and radar (Chatanika, Alaska) field of view in the premidnight sector, providing a unique opportunity to differentiate the enhanced convection and substorm expansion fields. The distributions of the calculated electric potential for the expansion and maximum phases of the substorm show the first clear evidence of the coexistence of two physically different systems in the global convection pattern. The changes in the convection pattern during the substorm indicate that the large‐scale potential distributions are indeed of general two‐cell patterns representing the southward IMF status, but the night‐morning cell has two positive peaks, one in the midnight sector and the other in the late morning hours, corresponding to the substorm expansion and the convection enhancement, respectively.

No abstract

Various ionospheric electrodynamic parameters for the period July 23–24, 1983, are calculated by using ground magnetic records from a total of 88 stations in the northern hemisphere. For this purpose, an “instantaneous” conductance distribution deduced from the DMSP‐F6 bremsstrahlung X ray image data is utilized. Since the conductance distribution is, for the first time, completely independent of ground magnetic data, it is a unique opportunity to examine some of the inherent ambiguity in the magnetogram‐inversion technique based on a statistically derived conductance model. Several important conclusions of this study are as follows: (1) The poleward portion of the westward electrojet in the morning sector is dominated by the electric field, while its equatorward portion is dominated by the ionospheric conductance. Although less definite, a reverse trend seems to pervade the eastward electrojet region in the dusk sector. (2) During a quiet or moderately disturbed period, the major electric potential pattern is roughly circumscribed by the auroral zone conductance belt with the subauroral zone being a substantially lower electric field region. (3) The global pattern of the equivalent current system resembles the electrical potential distribution during summer conditions. It may thus be possible to use the equivalent current system as a reasonable approximation of the electric potential distribution in studying the global pattern of magnetospheric convection for prevailing sunlit conditions. (4) The electric potential distribution consists generally of a smooth and well‐defined two‐cell convection pattern without any significantly localized structure. (5) A sunward convection flow is clearly identified over the polar cap region during strongly northward IMF periods. The multicell nature of the convection pattern is still unclear. (6) During strongly northward IMF periods, significant currents and Joule dissipation are observed in the polar cap region, indicating that the magnetosphere is far from its ground state. (7) The regions of intense Joule heating are generally confined to relatively narrow belts along the auroral electrojets, with the major heating region in the westward electrojet region shifted poleward and the one in the eastward electrojet region shifted equatorward. The Joule dissipation rate is relatively low in the local midnight sector. (8) The presently available statistical conductance models can be used, as a first approximation, to study global‐scale polar ionospheric electrodynamics. However, the fact that the statistical models cannot simulate an instantaneous situation severely restricts their usefulness for studying the spatial and temporal variations of individual substorms.