Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

INTRODUCTION. The identification of magnetоspheric sources of phenomena observed in the high latitude ionosphere is one success of space plasma physics that can be attributed, in part,' to the analysis of data gathered from numerous low altitude spacecraft. For more than a decade, energetic particle populations, magnetic field perturbations, plasma drifts and auroral images observed with low altitude, polar orbiting satellites have been assoc iated with specific regions of the distant magnetosphere. For example, Winningham et al. /1975/ intriduced the term "Boundary Р1азгаа Sheet" (BPS) and "Central plasma Sheet" (CPS) to describe characteristics of energetic electron populations that differ in morphology and spectra. These data were acquired at an altitude of 1400 km with the ISIS 2 satellite in the midnight sector auroral zone. BPS electrons in this sector were assumed to originate in what is known as the Plasma Sheet Boundary Layer while CPS electrons originate in the plasma sheet. llcDiarmid et al. /1978/ concluded, from their ISIS 2 observations of particles and magnetic fields in the dawn sector, that precip itating electrons with BPS characteristics originate in the Low Latitude Boundary Layer (LLBL). Heelis et al. /1980/, using ion drift and energetic particle data from Atmosphere Explorer C, have reported that electrons that exhibit the characteristics of the BPS/CPS interface in the ionosphere are statistically located within the auroral oval and this interface is equator- ward of the plasma convection reversal at nearly all local time. Therefore, from these earlier studies, we conclude that the BPS region in the dawn sector maps to the low latitude boundary layer in the magnetotail and that this region contains the region of reversal between tailward and sunward flowing plasma (see Figure 10 of Heelis et al.,1980). McDiarmid et al. /1978/ and Bythrow et al. /1981/ have presented evidence from particle and magnetic field measurements made by ISIS 2 and AE-C that shows that the Region 1 Birkeland current system generally extends poleward of the plasma convection reversal at most local times when the IMF is directed southward. This has been interpreted as evidence for a boundary layer source of at least a low-latitude poi’tion of the Region 1 current system. During the brief lifetime of the HILAT VUV auroral imager, about forty high resolution images of the aurora were obtained (Meng and Huffman, 1984). During this period (June and July 1983), HILAT was the only low-altitude satellite ever to provide this unique observation of particle, fields and imaging data. For a complete description of the HILAT satellite, its mission and instrumentation, see Fremouw et al. /1983/ and the John Hopkins APL Technical Digest 5, April 1984. In the following, we present the combined HILAT data set arising from a single polar pass consisting of VUV (1356 ft) imaging of the early morning auroral oval and simultaneous in-situ measurements of magnetic field perturb ations, energetic electrons and plasma drift velocity, acquired on 17 July 1983 from 10:21 to 10:29 UT. This is the same data set used by Doyle, et al. (1986) to study a new numerical model of auroral arc formation. A detailed examination of these data reveal a triplet of paired, oppositely-directed Birkeland currents embedded in the Region 1 current system. Associated with these current pairs, HILAT detected electron precipitation enhancements, gradients in the plasma drift velocity and discrete VUV emissions. The charac teristics of the energetic electrons surrounding the triplet of current pairs indicates that, if projected to the equatorial plane of the magnetotail, their magnetic footprints would map to the interface between the low-latitude boundary layer (LLBL) and the central plasma 3heet. 48