Low‐energy plasma observations at synchronous orbit

Lennartsson, W.; Reasoner, D. L.

doi:10.1029/ja083ia05p02145

Cited by 67 publications

(30 citation statements)

References 15 publications

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“…This behavior was also observed by the ATS 6 satellite in synchronous orbit and reported by Lennartsson and Reasoner [ 1978]. The maximum-to-minimum spread in counts in the radial or spinning head is greater than that for the other two heads.…”

Section: Plasma Datasupporting

confidence: 83%

Characteristics of low‐energy plasma in the plasmasphere and plasma trough

Reasoner¹,

Craven²,

Chappell³

1983

J. Geophys. Res.

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Data from the light ion mass spectrometer (LIMS) on the SCATHA satellite is used to study the low‐energy (<100 eV) plasma populations at a near‐geosynchronous orbit. The characteristics of the plasma in the noon to midnight sector during quiet to moderately active times are emphasized. The observed plasma populations tended to group into three distinct types. These were a warm trapped distribution, a warm field‐aligned distribution, and a distribution with kTi < 1 eV. The cold plasma was seen after 1800 LT during periods of magnetic quiet and was observed to be flowing sunward during active periods. The cold plasma is identified as encounters with the plasmasphere, while the warm plasma populations are assumed to lie outside of the plasmasphere in the plasma trough. The presence of these warm plasma populations may be responsible for the difference in the shape of the bulge‐region plasmasphere deduced from whistler measurements (Carpenter, 1966) and from in situ measurements made on OGO 5 (Chappell et al., 1970). The effects of the spacecraft potential upon the low‐energy plasma measurements is studied. A threshold effect may be operative whereby when the cold plasma density decreases to less than about 2 ions/cm³, the spacecraft potential rises to a positive value such that cold plasma fluxes are effectively excluded from detection.

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Section: Plasma Datasupporting

confidence: 83%

Characteristics of low‐energy plasma in the plasmasphere and plasma trough

Reasoner¹,

Craven²,

Chappell³

1983

J. Geophys. Res.

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“…The ambient plasma densities measured during the DFI events on REV 619 and REV 1398 were -•10 cm -3 and -• 10 2 cm -3 respectively (F. S. Mozer, private communication). Values of-• 1 cm -3 are not unusual for the regions at or beyond the synchronous orbit [Lennartsson and Reasoner, 1978;Gurnett and Frank, 1974]. Since the ambient plasma conditions are generally adequate to produce detectable DFI's we conclude from the low frequency of occurrence of these DFI events that if downward directed quasi-static parallel electric fields involving potential drops ->500 V occur in the altitude range from 2000 km to -•3 Re they are an infrequent phenomenon.…”

Section: Statistical Features Of Downward Flowing Ion Eventsmentioning

confidence: 70%

Downward flowing ions and evidence for injection of ionospheric ions into the plasma sheet

Ghielmetti¹,

Sharp²,

Shelley³

et al. 1979

J. Geophys. Res.

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Energetic (keV) protons and 0+ ions with field aligned pitch angle distributions and peak fluxes up to ∼ 7 × 107 (cm² s sr keV)−1 have been observed streaming downward in the high altitude (∼ 1 RE) auroral ionosphere. In two examples described in detail, the correlations observed between the downward flowing and coincident trapped ion populations suggest a common origin. Downward flowing ion events are a much less frequent phenomenon than upward flowing ion events in the auroral region. The significant difference implies that the energetic upward flowing ions from the auroral ionosphere are commonly injected into the trapped population of the plasma sheet, and furthermore that parallel electric fields involving potential drops of ≳500 V are directed preferentially upward in the altitude range from 2000 km to ∼ 3 RE. Spatially localized regions of enhanced hot (∼keV) plasma density were frequently observed in the low L portion of the plasma sheet. The statistical location of these ‘plasma clouds’ correlates well with the substorm injection boundary near dusk inferred by McIlwain (1974) and with the upward flowing ion events observed at ∼ 1 RE altitude (Ghielmetti et al., 1978a, b). The downward flowing ion events occurred preferentially within such ‘plasma clouds.’ The results described in this paper suggest that upward flowing ions from the auroral acceleration regions are responsible for both the downward flowing ions and for at least some of the plasma clouds. A significant fraction of the equatorial substorm injected plasma clouds may thus result from this ionospheric source region.

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“…Hence, only one field line direction could be observed. Multiple studies of the ATS‐6 data [ Lennartsson and Reasoner , 1978; Horwitz and Chappell , 1979; Horwitz , 1980; Comfort and Horwitz , 1981] showed the spatial and energy distributions of the different types of pitch angle distributions in the inner magnetosphere. The field‐aligned distributions in the 20–400 eV range were found to have half angle spreads of 20–30 degrees and to be found with up to 90% probability in the morning sector.…”

Section: Observations Related To the Warm Plasma Cloakmentioning

confidence: 99%

Observations of the warm plasma cloak and an explanation of its formation in the magnetosphere

et al. 2008

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[1] Previous studies of the magnetospheric plasma populations have concentrated on the low-energy (1 eV) plasma of the plasmasphere, the more energetic (1-100 keV) plasma of the plasma sheet and ring current, and the high-energy (approximately MeV) plasma of the radiation belts. A compilation of satellite measurements over the past 30 years augmented by recent observations from the Polar-TIDE instrument has revealed a new perspective on a plasma population in the middle magnetosphere. This population consists of ions with energies of a few eV to greater than several hundred eV which display a characteristic bidirectional field-aligned pitch angle distribution. Measurements from the ATS, ISEE, SCATHA, DE, and POLAR satellites establish the characteristics of this ''warm plasma cloak'' of particles that is draped over the nightside region of the plasmasphere and is blown into the morning and early afternoon dayside sector by the sunward convective wind in the magnetosphere. The satellite observations combined with the predictions of an ion trajectory model are used to describe the formation and dynamics of the warm plasma cloak.

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Low‐energy plasma observations at synchronous orbit

Cited by 67 publications

References 15 publications

Characteristics of low‐energy plasma in the plasmasphere and plasma trough

Characteristics of low‐energy plasma in the plasmasphere and plasma trough

Downward flowing ions and evidence for injection of ionospheric ions into the plasma sheet

Observations of the warm plasma cloak and an explanation of its formation in the magnetosphere

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