The geosynchronous ATS 6 environmental measurements experiment was operated during 15 evening passes when the SCATHA spacecraft was within 1-2 RE and both spacecraft were very near the geomagnetic equator. Numerous, well-defined substorm injections were recorded at both spacecraft with varying local time and radial separations. Accurate delay timing was possible since these events exhibit abrupt and essentially dispersionless (to within 10 s) plasma flux changes which replace cool preexisting plasma with hot quasi-Maxwellian distributions. The hot plasma propagates earthward in close association with an equally abrupt magnetic field increase at velocities in the range of 10-100 km/s. On this basis we identify the agent of injection as the induced electric field of the earthward propagating compression wave observed by Russell and McPherron (1973), and we refer to the propagating particle structure as the injection front. These dramatic synchronous orbit electron injection signatures are produced mainly by a boundary motion rather than by local acceleration of plasma. However, we find some evidence that the plasma sheet electrons are weakly 'heated' by the passage of each compression wave, the energy appearing mainly in the high-energy tail of the distribution. The spectral change we observe argues convincingly that the boundary in question is a precipitation-flow boundary layer (Kennel, 1969) and that the near-earth plasma sheet is significantly degraded in average energy by the addition of ionospheric plasma, especially secondary electrons emitted by the ionosphere due to precipitating energetic electrons. The presence of significant •B/•t requires that a change of mapping occur between the equatorial plane and the ionosphere, the sense being such as to map the inward moving injection front to a relatively fixed latitude in the ionosphere. Such an earthward plasma injection would not therefore require equatorward auroral motion. tionary orbit can be reproduced equally well by an injection boundary model, or a model with varying convection electric field, or a hybrid model with spatially limited time-varying electric and magnetic fields [Kivelson et al., 1980, and refer-Copyright ¸ 1981 by the American Geophysical Union. Paper number IA0733. 0148-0227/81/00 IA-0733501.00 • ences therein]. This situation illustrates the nonuniqueness of conclusions drawn from a single-satellite data set and the need for multiple-satellite observations to constrain the modeling process. This paper is an attempt to learn from the comparison of plasma data sets from ATS 6 and SCATHA relating to several substorm events. An example of the success of the first point of view appears in the paper by Barfield et al. [1977], in which an impulsive injection of plasma is observed at ATS 5 and then 11 rain later at Explorer 45, 1.2 RE earthward and at approximately the same local time. Assuming that an energetic plasma was created and released beyond a sharp, azimuthally extended boundary outside synchronous orbit, the authors were able to bui...

A detailed signature for individual substorms is sought in the interplanetary medium. Hourly values of interplanetary field and plasma parameters are correlated with hourly averages of the AE index. An interplanetary variable involving the southward component of the interplanetary field in the solar magnetospheric coordinate system is shown to be singularly important for the generation of substorms. The parameter best correlated with AE (0.8 correlation coefficient) is the integral or summation of Bz south over time for the hour preceding the AE hourly average. The magnitude of this integral appears to be linearly related to the hourly average of AE. The linearity suggests that the southward interplanetary field represents a continuing dynamic mechanism for the production of substorms rather than just being a trigger for the release of energy that has been stored in the magnetospheric tail. Furthermore, the additional energy that the southward component of the interplanetary field apparently puts into the tail is not accumulated for longer than about 1 hour before it appears as a substorm. A linear fit to AE that uses interplanetary parameters is obtained for two time intervals of data.

[1] Analysis of high time resolution magnetometer data from the Polar satellite and from an array of high-latitude ground stations in Antarctica has identified 20 simultaneously observed Pc 1-2 wave events in the outer dayside magnetosphere during the first 17 months of Polar operations. In contrast to most earlier satellite studies of Pc 1-2 waves, based on data from equatorial satellites near apogee which moved only slowly across L shells if at all, the initial orbit of Polar allowed it to rapidly cross outer magnetospheric L shells, but significantly away from the magnetic equator. Consistent with several previous studies of outer magnetospheric Pc 1-2 waves, the majority of these events (75%) were associated with significant compressions of the magnetosphere. Seven of the events occurred simultaneously in satellite and ground data, with wave bursts temporally associated with compressions. These events, most at L values > 9, confirm the suggestion of Anderson and Hamilton [1993] that the outer dayside magnetosphere is often near marginal stability for electromagnetic ion cyclotron (EMIC) wave generation, so waves can be stimulated by even modest magnetospheric compressions. However, 10 of the wave events (five associated with compressions, and five not) were highly localized in L shell. In these ''spatially localized'' cases, continuous wave emissions were seen on the ground for extended periods of time, while in space waves were observed for only a few minutes and occurred only in radially narrow regions. The noncompressional events, all spatially localized, appear to be the first examples identified in space of the class of wave events known as Pc 1-2, sustained narrowband emissions which have durations at high-latitude ground stations of the order of 10 hours in the day and dusk local time sectors. All 10 of the spatially localized events, whether compressional or not, followed intervals of at least 12 hours of sustained very quiet magnetospheric conditions. Energetic ion observations from Polar confirm earlier suggestions that drifting plasma sheet ions are the source of dayside Pc 1-2 waves in the outer dayside magnetosphere, but they also show different particle configurations for the spatially localized and temporally ordered event categories. Events in both categories occurred within radially extended regions with ring-like, moderately anisotropic distributions of !5 keV protons and with deep minima in the flux distributions at energies <5 keV. However, spatially localized wave events occurred only in association with radially localized regions that also contained highly anisotropic fluxes of $0.5-3 keV protons, at a considerable distance from the magnetospheric boundary. In contrast, no such radial structure was evident in any of the temporally ordered events, or in three ''uncertain'' events. The association of the spatially localized events with highly structured populations of plasma sheet protons of keV and higher energies indicates an important but unanticipated role for these protons in destabi...

We have used magnetometer data from 10 locations in Arctic Canada and Greenland, covering over 5 hours in magnetic local time at magnetic latitudes from 75 ø to 79 ø, to characterize the dayside patterns of enhanced long-period ULF (10-to 600-s period) wave power at cusp/cleft latitudes. We conclude the following: (1) In agreement with earlier single-station studies, we find that the most common wave type is broadband noise (Pi 1-2).Distinct Pc 3-4 activity and more sustained monochromatic Pc 5 activity are most apparent when this broadband noise is weak. (2) Multistation observations also make clear that strong, broadband Pi 1-2 signals are both temporally and spatially structured: Although their amplitude is somewhat larger near local noon and near nominal cusp latitudes, they often occur simultaneously (to within a few minutes) at all stations. They are thus not local signals, and c.annot be interpreted as evidence of passage of an auroral region or boundary over an individual magnetic observatory. In particular, we have found no evidence for a distinctive "cuSp" signature in broadband ULF waves in this frequency range. (3) The occurrence of strong broadband Pi 1-2 signals at these latitudes appears to be controlled largely by solar wind velocitY. We found good correlations between the occurrence of strong Pi 1-2 signals and high solar wind velocity, and we also noted some dependence on the cone angle of the interplanetary magnetic field for moderate to low solar wind velocities. We .speculate that there •may be an additional dependence on enhanced levels of trapped plas ma in regions topologically connected to the very high latitude dayside ionosphere, such as the entry layer, high-latitude dayside field minimum regions, or plasma mantle. Available satellite data on the level of trapped energetic electron fluxes at geosynchronous orbit showed that broadband power levels appeared to correlate with enhanced flux levels on the time scale of days, but not on shorter time scales, suggesting that any such dependence is not directly related to substorm injections.The ionospheric foot point of the cusp/cleft region of the near the cusp/cleft region for only a short interval each day. As Earth's magnetosphere is connected, via magnetic field lines, to aresuit, inferences from Single stations about the origin of wave the entire dayside boundary layer and magnetopause. Because signatures in the cusp/cleft region, and wheth er they are presatellite orbits allow only brief crossings through this complex dominantly temporal or spatial, must be confirmed before these and critical region, ground-based magnetometers can play an signatures can be used as reliable diagnostics of remote proimportant role in providing synoptic coverage of processes at cesses. Further, use of data from a single station, or in some the boundary between the solar wind and the Earth's space cases chains of stations separated in latitude but at nearly fixed environment, if their signatures can be identified and calibrated. longitude, can provide only ...

A series of recent studies of Pc 3 magnetic pulsations in the dayside outer magnetosphere has given new insights into the possible mechanisms of entry of ULF wave power into the magnetosphere from a bow shock related upstream source. In this paper we first review many of these new observational results by presenting a comparison of data from two 10‐hour intervals on successive days in April 1986 and then present a possible model for transmission of pulsation signals from the magnetosheath into the dayside magnetosphere. Simultaneous multi‐instrument observations at South Pole Station, located below the cusp/cleft ionosphere near local noon, magnetic field observations by the AMPTE CCE satellite in the dayside outer magnetosphere, and upstream magnetic field observations by the IMP 8 satellite show clear interplanetary magnetic field field magnitude control of dayside resonant harmonic pulsations and band‐limited very high latitude pulsations, as well as pulsation‐modulated precipitation of what appear to be magnetosheath/boundary layer electrons. We believe that this modulated precipitation may be responsible for the propagation of upstream wave power in the Pc 3 frequency band into the high‐latitude ionosphere, from whence it may be transported throughout the dayside outer magnetosphere by means of an “ionospheric transistor.” In this model, modulations in ionospheric conductivity caused by cusp/cleft precipitation cause varying ionospheric currents with frequency spectra determined by the upstream waves; these modulations will be superimposed on the Birkeland currents, which close via these ionospheric currents. Modulated region 2 Birkeland currents will in turn provide a narrow‐band source of wave energy to a wide range of dayside local times in the outer magnetosphere.