Density structures inside the plasmasphere: Cluster observations

Darrouzet, F.; Décréau, Pierrette; Keyser, Johan De; Masson, A.; Gallagher, D. L.; Santolı́k, O.; Sandel, B. R.; Trotignon, Jean-Gabriel; Rauch, Jean-Louis; Guirriec, E. Le; Canu, P.; Sedgemore, F.; André, Mats; Lemaire, J.

doi:10.5194/angeo-22-2577-2004

Cited by 66 publications

(73 citation statements)

References 46 publications

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“…Rather than ruling out this theory, we think that the perspective of an undulated plasmapause surface, associated with a range of density gradient directions, is quite acceptable. The existence of variable density gradient directions within a small volume in the plasmapause region has recently received direct confirmation by Cluster observations (Darrouzet et al, 2004).…”

Section: Case Of 25 July 2002: Nightside Magnetospherementioning

confidence: 83%

Observation of continuum radiations from the Cluster fleet: first results from direction finding

et al. 2004

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Abstract. The Cluster fleet offers the first possibility of comparing non-thermal terrestrial continuum radiation from similarly equipped nearby observation points. A very rich data set has already been acquired on the Cluster polar orbit, between 4 and 19 Earth radii geocentric distances, and preliminary analysis has been carried out on these emissions. We focus in this paper on direction finding performed from all four spacecraft as a means to locate the position of the sources of this continuum radiation. Directions are derived from spin modulation properties, under the usual analysis assumptions of the wave vector of the radiation lying in the plane containing the spin axis and the antenna position at electric field minimum. All the spin axes of the four Cluster spacecraft are aligned perpendicular to the ecliptic, thus the aligned spacecraft antenna spin planes provide redundant 2-D views of the propagation path of the radiation and source location. Convincing 2-D triangulation results have been obtained in the vicinity of the source region. In addition, the out of spin plane component of the wave vector reveals itself to a certain extent through directivity characteristics compared at different distances of the spin plane to the ecliptic. The four case events studied (two of them taken near apogee, the other two near perigee) have confirmed general properties derived from previous observations: trapping in the lower frequency range, radiation escaping into the magnetosheath region in the higher frequency range. All propagation directions are compatible with source positions in the plasmapause region, however, at a significant distance from the equator in one case. Our observations have also revealed new properties, like the importance of small-scale density irregularities in the local amplification of continuum radiation. We conclude that more detailed generation and propagation models are needed to fit the observations.

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Section: Case Of 25 July 2002: Nightside Magnetospherementioning

confidence: 83%

Observation of continuum radiations from the Cluster fleet: first results from direction finding

et al. 2004

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“…Spacecraft potential is a very good proxy of the total electron density [Pedersen et al, 2001;Darrouzet et al, 2004]: the high flux of ambient electrons in the plasmasphere brings the spacecraft potential to only a few volts positive relative to the plasma; in the lobes, however, the electron flux is very low and the spacecraft goes very positive (to +50 V or more), because of photoelectron emission. As confirmed by the spacecraft potential values, both spacecraft encountered, after about 1200 UT, a very diffuse plasmasphere boundary layer with a gradual increase of plasma density, which is typical of extended periods of relatively quiet geomagnetic conditions.…”

Section: Dandouras Et Al: Inner Magnetosphere Energetic Ionsmentioning

confidence: 99%

Energetic ion dynamics of the inner magnetosphere revealed in coordinated Cluster‐Double Star observations

Dandouras

Cao²,

Vallat

2009

J. Geophys. Res.

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[1] Since early 2004 the Chinese spacecraft Tan Ce 1 (TC-1), first component of the Double Star (DSP) mission, has been on an equatorial elliptical orbit (13.4 R E apogee), allowing the study of the dynamics of the Earth's magnetosphere in conjunction with the four European Cluster spacecraft (19.6 R E apogee). The Cluster and Double Star spacecraft orbits are such that the spacecraft are almost in the same meridian, allowing conjugate studies. The four Cluster spacecraft highly eccentric polar orbit at 4 R E perigee permits them to sample the ring current, the radiation belts, and the outer plasmasphere from south to north, almost following the same magnetic flux tube (latitudinal profile), whereas TC-1, with its very low-perigee equatorial orbit, gives the plasma profile across L shells. Coordinated ion measurements provided by the Cluster Ion Spectrometry and Hot Ion Analyzer instruments onboard Cluster and TC-1, respectively, obtained during quiet conditions, disturbed geomagnetic conditions, and an intense storm, are used to analyze crossings of the plasmasphere and the ring current region. Multiple narrow ion energy bands (''nose-like'' structures) are simultaneously observed by both Cluster and TC-1. These observations reveal the large-scale character of these structures and pose a challenge for the simulation and modeling of the inner magnetosphere populations.

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“…CRRES (Combined Release and Radiation Effects Satellite) measured density fluctuations with a spectral power-law index of −5/3 (LeDocq et al, 1994). Density irregularities exist inside the plasmasphere measured by Cluster (Darrouzet et al, 2004). The small-scale density structures inside PBL (plasmasphere boundary layer) are one of the research topics discussed by Carpenter and Lemaire (2004).…”

Section: Introductionmentioning

confidence: 99%

Multi-spacecraft observations of small-scale fluctuations in density and fields in plasmaspheric plumes

et al. 2012

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Abstract. In this event study, small-scale fluctuations in plasmaspheric plumes with time scales of ∼10 s to minutes in the spacecraft frame are examined. In one event, plasmaspheric plumes are observed by Cluster, while IMAGE measured density enhancement at a similar location. Fluctuations in density exist in plumes as detected by Cluster and are accompanied by fluctuations in magnetic fields and electric fields. Magnetic fluctuations are transverse and along the direction of the plumes. The E/B ratio is smaller than the Alfvén velocity. Another similar event is briefly presented. We then consider physical properties of the fluctuations. Alfvén mode modulated by the feedback instability is one possibility, although non-local generation is likely. It is hard to show that the fluctuations represent a fast mode. Interchange motion is possible due to the consistency between measurements and expectations. The energy source could be a pressure or density gradient in plasmaspheric plumes. When more events are accumulated so that statistical analysis becomes feasible, this type of study will be useful to understand the time evolution of plumes.

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Density structures inside the plasmasphere: Cluster observations

Cited by 66 publications

References 46 publications

Observation of continuum radiations from the Cluster fleet: first results from direction finding

Observation of continuum radiations from the Cluster fleet: first results from direction finding

Energetic ion dynamics of the inner magnetosphere revealed in coordinated Cluster‐Double Star observations

Multi-spacecraft observations of small-scale fluctuations in density and fields in plasmaspheric plumes

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