Multisatellite data are used to examine the temporal relationship between Subauroral Ion Drifts (SAID) and the phases of an auroral substorm. Utilizing images of auroral luminosities taken by the Dynamics Explorer 1 (DE 1) spacecraft and observations of particle injection at geosynchronous orbit, we identify the time of expansive phase onset and estimate the time at which recovery begins. Noting the times at which SAID are observed simultaneously by the DE 2 spacecraft, we find that SAID typically occur well after substorm onset (more than 30 min), during the substorm recovery phase. Substantial westward ion drifts and field‐aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm, but the drifts lack the narrow spike signature associated with SAID. Prior to substorm onset and after substorm recovery, field‐aligned currents are absent equatorward of the auroral oval and the ionosphere is very nearly corotating. A phenomenological model of SAID production is proposed that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship. In this model, substorm‐generated, subauroral field‐aligned currents close via Pedersen currents with the outward flowing, region 1 currents at higher latitudes. These Pedersen currents flow in the region of low conductivity equatorward of the auroral oval and are associated with relatively large, poleward directed electric fields. The frictional heating of the ions caused by collisions with the corotating neutral atmosphere substantially increases the rate of ion‐atom interchange between O+ and N2. Subsequent fast recombination of NO+ with electrons further reduces the subauroral F region conductivities with a corresponding increase in the electric field and the frictional heating. This heating leads to thermal expansion, substantial field‐aligned plasma flow, and very large depletions in the F peak concentration, thus additionally reducing the height‐integrated Pedersen conductivity.

Measurements from the Lepedea plasma instruments and the flux gate magnetometers on ISEE 1 and 2 are used to examine the nature of the hydromagnetic waves associated with the various classes of ions backstreaming from the earth's bow shock. The reflected ions, which are confined to a narrow energy and angular range, are accompanied by small amplitude (≲½γ peak to peak) left‐handed waves at frequencies close to 1 Hz in the spacecraft frame. Diffuse backstreaming particles with a broad energy spectrum are associated with low frequency (∼ 30‐s period) large amplitude (∼5γ peak to peak) waves. Intermediate particles are associated with a mixture of these two wave types. Often the waves associated with the diffuse beams steepen as if they were mini shocks. The leading edge (trailing edge in the spacecraft frame) frequently appears to break up into a whistler mode wave packet. These discrete wave packets are right‐hand polarized and have frequencies from below the proton gyrofrequency to well above it in the plasma frame and are blown back towards the earth by the solar wind.

In this study we identify the principal types of plasma waves which occur in the distant magnetotail, and we investigate the relationship of these waves to simultaneous plasma and magnetic field measurements made on the same spacecraft. The observations used in this study are from the Imp 8 spacecraft, which passes through the magnetotail at radial distances ranging from about 23.1 to 46.3 Re. Three principal types of plasma waves are detected by Imp 8 in the distant magnetotail: broad band electrostatic noise, whistler mode magnetic noise bursts, and electrostatic electron cyclotron waves. The electrostatic noise is a broad band emission which occurs in the frequency range from about 10 Hz to a few kilohertz and is the most intense and frequently occurring type of plasma wave detected in the distant magnetotail. This noise is found in regions with large gradients in the magnetic field near the outer boundaries of the plasma sheet and in regions with large plasma flow speeds, 11Y km s -1, directed either toward or away from the earth. The whistler mode magnetic bursts observed by Imp 8 consist of nearly monochromatic tones which last from a few seconds to a few tens of seconds. These noise bursts occur in the same region as the broad band electrostatic noise, although much less frequently, and are thought to be associated with regions carrying substantial field-aligned currents. Electrostatic electron cyclotron waves are seldom detected by Imp 8 in the distant magnetotail. Although these waves occur very infrequently, they may be of considerable importance, since they have been observed in regions near the neutral sheet when the plasma is extremely hot.

We present a study of the low‐latitude boundary layer (LLBL) using ISEE 1 energetic particle, plasma, and magnetic field data obtained during numerous traversals of the LLBL that occurred on 66 ISEE 1 passes through the magnetospheric flank LLBL region. We use energetic particle distributions to determine dawn and dusk LLBL behavior and topology for varying orientations of the magnetosheath and/or interplanetary magnetic field (M/IMF), for different local times, and for changing levels of geomagnetic activity (Kp). This study corroborates and extends the earlier work of Williams et al. (1985) who presented a detailed study of two (dusk and dawn) ISEE 1 passes through the LLBL region for the case of northward M/IMF. We find that the dawn and dusk LLBL are on closed geomagnetic field lines for northward M/IMF but are on a combination of closed and open field lines for a southward M/IMF. The energetic particle distributions show that cases of reverse‐draped field lines in the LLBL are consistent with an open field line topology. In addition, we find that the LLBL is thicker (thinner) for northward (southward) M/IMF and becomes thicker with increasing distance from the subsolar point. LLBL electric fields nominally are in the few (3–5) millivolts per meter range and display an apparent maximum value of ∼10 mV/m. These electric fields capture magnetospherically drifting particles as they approach the LLBL and propel them tailward. In this way, the plasma sheet is the dominant source of energetic (≳10 keV) particles in the LLBL while the magnetosheath appears to be the dominant source for lower‐energy (≲10 keV) LLBL particles.

The plasma sheet boundary layer is a temporally variable transition region located between the magnetotail lobes and the central plasma sheet. We have made a survey of these regions by using particle spectra and three‐dimensional velocity‐space distributions sampled by the ISEE 1 LEPEDEA. Ion composition measurements obtained by the Lockheed ion mass spectrometers indicate that ionospheric ions play a crucial role in magnetotail dynamics. Eleven crossings from the lobes to the central plasma sheet taken at various local times and levels of geomagnetic activity are analyzed in detail. The average ratios of He+/H+, He++/H+, and O+/H+ are not significantly different between the plasma sheet boundary layer and central plasma sheet. Densities and temperatures intermediate between the central plasma sheet and lobes are observed in the plasma sheet boundary layer although bulk flow speeds there are typically enhanced. Counter‐streaming ion beams are often observed in the plasma sheet boundary layer at energies of ∼1 keV/q to >45 keV/q. Intense antisunward‐flowing beams of ionospheric origin at E/q of <1 kV are often seen in the tail lobes, the plasma sheet boundary layer, and, infrequently, in the central plasma sheet. Such beams are not commonly observed in the central plasma sheet, which is characterized by hotter and more isotropic ion and electron distributions. Our samples of ion distributions in the plasma sheet boundary layer frequently show an evolution of distribution functions from highly anisotropic single beams or counter‐streaming beams toward the more isotropic distributions typical of the hot component of the central plasma sheet. Provided that the acceleration process for these beams can be identified, we can then account for the transport and injection of hot plasma into the central plasma sheet. We conclude that the plasma sheet boundary layer is a primary transport region of the magnetotail.

The characteristics of the hrge-scale electrodynamic parameters, field-aligned currents (FACs), electric fields, and electron prec/pitation, which are associated with auroral substorm events in the nighttime sector, have been obtained through a unique analysis which places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images. A generic bulgetype auroral emission region has been deduced from auroral images taken by the Dynamics Explorer I (DE 1) satellite during a number of isolated substorms, and the form has been divided into six sectors, based on the peculiar emission characteristics in each sector: west of bulge, surge horn, surge, middle surge, eastern bulge, and east of bulge. By comparing the location of passes of the Dynamics Explorer 2 (DE 2) satellite to the simultaneously obtained auroral images, each pass is placed onto the generic aurora. The organization of DE 2 data in this way has systematically clarified peculiar characteristics in the electrodynamic parameters. An upward net current mainly appears in the surge, with litfie net current in the surge horn and the west of bulge. The downward net current/s distributed over wide longitudinal regions from the eastern bulge to the east of bulge. Near the poleward boundary of the expanding auroral bulge, a pair of oppositely directed FAC sheets is observed, with the downward FAC on the poleward side. This downward FAC and most of the upward FAC in the surge and the middle surge are associated with narrow, intense antisunward convection, corresponding to an equatorward d/rected spikelike electric field. This pair of currents decreases in amplitude and latitudinal width toward dusk in the surge and the west of bulge, and the region 1 and 2 FACs become embedded in the sunward convection region. The upward FAC region associated with the spikelike field on the poleward edge of the bulge coincides well with intense electron precipitation and aurora appearing in this western and poleward portion of the bulge. The convection reversal is sharp in the west of bulge and surge horn sectors, and near the high-latitude boundary of the upward region I FAC. In the surge, the convection reversal is near the low-latitude boundary of the upward region 1, with a near stagnation region often extending over a large interval of latitude. In the eastern bulge and east of bulge sectors, the region I and 2 FACs are located in the sunward convection region, while a spikelike electric field occasionally appears poleward of the aurora but usually not associated with a pair of FAC sheets. In the eastern bulge, magnetic field data show complicated FAC distributions which correspond to current segments and filamentary currents. INTRODUCTION Auroral substorms are defined by a systematic sequence of auroral motions and magnetic disturbances [Akasofu, 1964]. Since field-aligned currents (FACs), ionospheric electric fields or convection, charged particle precipitation, and resulting ionospheric conductivity are closely...

First observations of the plasmas in the dayside polar magnetosphere were obtained with the earth-satellite IMP 5 during July -August 1969. Several of the more important observational results are: the polar neutral 'points' which appear at the high-latitude magnetopause in mathematical models for the shape of the geomagnetic cavity formed by the interaction of the solar wind with the geomagnetic field are observationally 'bands' with width Q 1 R across the dayside high-latitude magnetopauge (one 'band' in the Northern hemisphere and presumably a second in the Southern hemisphere) I these two 'bands', or regions of the magnetopause through which the magnetosheath plasma has direct access to the magnetosphere.. and the corresponding extension of these bands from magnetopause to auroral altitudes have been designated herein as the 'polar cusps', at all other positions of the dayside magnetopausep the magnetopause appears to be an effective barrier against the direct entry of magnetosheath plasmap during periods of relative magnetic quiescence the intersection of the dayside polar cusp with the auroral zone is positioned at invariant latitude A = 7 9 " (-+ 1") and its latitudinal width is 10 to 30 km projected onto the auroral zone during periods of relative magnetic disturbance the position of the polar cusp moves equatorward by several degrees in invariant latitude without a large increase in its latitudinal width, i.e., by factors < 2 .i the high-latitude termination of energetic trapped electron (E > 45 keV) intensities in the high-latitude dayside outer radiation zone occurs coincident with the polar cusp, albeit these intensities are small and of irregular profile with radial distance in this region, no measurable intensities of energetic electrons (E > 40 keV) magnetosheath protons and electronsp and ring-current protons were observed at latitudes above the polar cuspl i.e., in the polar cap region, the proton and electron differential energy spectrums as viewed in the solar direction in the distant polar cusp (within several earth radii of the magnetopause) are identical to those observed within the magnetosheath to within observational accuracy,.the bulk velocity of protons in the distant polar cusp as deduced from the angular distributions appears to be lower than that of the magnetosheath plasma near the magnetopause by factors -2 or 3 , in the mid-altitude polar cusp at -4 to 5 R geocentric radial distances, the proton specgrum differs from that at the magnetosheath in that protons with energies 6 500 eV are severely less than those observed in the magnetosheath, the proton spectrums in the mid-altitude polar e similar to those in the distant plasma ith the exception that the proton number densities in the polar cusp are typically larger by factors Q 2 0 to 200, the angular distributions of proton intensities in the mid-altitude polar cusp are strongly peaked along the l o c a l magnetic field ( i a e a R down into the auroral zone); the dimensions of the atmospheric loss cone at these altitudes ...

Preliminary examination of the first global auroral images gained with the vacuum‐ultraviolet imaging photometer on board DE 1 reveals a remarkable spatial configuration of auroral luminosities. Frequently the northern auroral oval is bifurcated by a sun‐aligned arc extending from the midday auroral zone to the nighttime sector of the oval. Simultaneous plasma measurements with the low‐altitude DE‐2 spacecraft are used to show that the character of plasmas above the polar arc is similar to those found over the poleward zones of the auroral oval. The spatial distribution of auroral luminosities is suggestive of a two‐cell structure of current systems and convection electric fields over the earth's polar cap and a similar division of the corresponding lobe in the magnetotail.