On the origin of kilometric continuum

Green, James L.

doi:10.1029/2001ja000193

Cited by 34 publications

(51 citation statements)

References 27 publications

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“…This theory, which in this case would give a small angle of about 20 • , has not been confirmed in practice, because the model (a single point source) and a suitable observatory (crossing two beams of small angular size, issued from the same source) are not met in reality (Morgan and Gurnett, 1991;Grimald et al, 2007). Observations from Green et al (2002) suggest that a density notch formed in the plasmasphere body can focus radio emissions along a beam of reduced angular size. Both approaches suggest a beam radiating along a direction not far from normal to the main, large scale, plasmapause surface.…”

Section: Morphologymentioning

confidence: 94%

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

Décréau¹,

Kougblénou²,

Lointier³

et al. 2013

Ann. Geophys.

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Abstract. The Cluster mission operated a "tilt campaign" during the month of May 2008. Two of the four identical Cluster spacecraft were placed at a close distance (∼ 50 km) from each other and the spin axis of one of the spacecraft pair was tilted by an angle of ∼ 46 • . This gave the opportunity, for the first time in space, to measure global characteristics of AC electric field, at the sensitivity available with long boom (88 m) antennas, simultaneously from the specific configuration of the tilted pair of satellites and from the available base of three satellites placed at a large characteristic separation (∼ 1 R E ). This paper describes how global characteristics of radio waves, in this case the configuration of the electric field polarization ellipse in 3-D-space, are identified from in situ measurements of spin modulation features by the tilted pair, validating a novel experimental concept. In the event selected for analysis, non-thermal continuum (NTC) waves in the 15-25 kHz frequency range are observed from the Cluster constellation placed above the polar cap. The observed intensity variations with spin angle are those of plane waves, with an electric field polarization close to circular, at an ellipticity ratio e = 0.87. We derive the source position in 3-D by two different methods. The first one uses ray path orientation (measured by the tilted pair) combined with spectral signature of magnetic field magnitude at source. The second one is obtained via triangulation from the three spacecraft baseline, using estimation of directivity angles under assumption of circular polarization. The two results are not compatible, placing sources widely apart. We present a general study of the level of systematic errors due to the assumption of circular polarization, linked to the second approach, and show how this approach can lead to poor triangulation and wrong source positioning. The estimation derived from the first method places the NTC source region in the dawn sector, at a large L value (L ∼ 10) and a medium geomagnetic latitude (35 • S). We discuss these untypical results within the frame of the geophysical conditions prevailing that day, i.e. a particularly quiet long time interval, followed by a short increase of magnetic activity.

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Section: Morphologymentioning

confidence: 94%

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

Décréau¹,

Kougblénou²,

Lointier³

et al. 2013

Ann. Geophys.

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“…Concerning a possible boundary in azimuth, one should note that continuum sources are probably drifting according to plasmasphere corotation. Green et al, 2002, for example, describe a case event when the radiation is produced in a narrow emission cone confined to the longitudinal extent of a plasmasphere bite out, observed to corotate with the plasmasphere. In the case of the Cluster event we are discussing (23 April 2002), there is no sign that the emission cone is narrow (the observed range in directivity directions is quite large), but it is still reasonable to consider co-rotation as the first order movement of the source.…”

Section: Case Of 7 June 2003: Magnetosheathmentioning

confidence: 99%

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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“…The observed longitudinal distribution of the kilometric radiation obtained from PIXIE X-ray data provides information on the source of the KC. Ray-tracing calculations [Green et al, 2002] show that the longitudinal distribution may Figure 13. A 3-hour Geotail PWI spectrogram from about 11 UT to 14 UT on 1 August 2001.…”

Section: Discussionmentioning

confidence: 99%

“…Normal continuum extends down to $5 kHz. Since the original investigation of KC [Hashimoto et al, 1999], there have been several studies of this phenomenon [e.g., Green et al, 2002Green et al, , 2004Menietti et al, 2003;Green and Fung, 2005;Hashimoto et al, 2005aHashimoto et al, , 2005bHashimoto et al, , 2006. The components of KC are enhanced at a relatively constant frequency over the same range as auroral kilometric radiation (AKR), which displays predominantly temporal variations in frequency [Calvert, 1981;Farrell and Gurnett, 1985;Farrell et al, 1986].…”

Section: Introductionmentioning

confidence: 99%

Observed X‐rays associated with kilometric continuum

et al. 2007

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[1] Kilometric continuum (KC) is a recently identified nonthermal magnetospheric radio/plasma wave phenomenon that consists of many narrowband emission lines of nearly constant frequency. The temporal structures of the KC wave intensities measured from the Geotail satellite in near equatorial positions at geocentric distances of 9-30 Earth radii were, on several occasions, similar to the temporal structures of X-rays simultaneously emitted from the atmosphere and mapped in position from the Polar satellite at lower altitudes and at high latitudes. The similarity in behavior of KC waves and X-rays might result from the fact that bremsstrahlung X-rays can be generated in the atmosphere by precipitating electrons produced at high altitudes by incident KC waves. KC waves at low latitudes appear correlated with X-rays at high latitudes. Our study supports the premise that KC waves interacting with high-altitude energetic electrons can lead to the production of X-rays at low altitudes from the resultant precipitation of the electrons. Thus the Polar and Geotail satellites may be used to map the spatial spread of KC, a feat that cannot be currently accomplished with waves observed from a single satellite. In this investigation, it is found that the X-ray emissions extend over a wide range of latitudes and may span a broad longitudinal interval. The energy spectra of X-rays emitted from the Earth at the times of KC events have been examined and found to display a wide variety of intensities and spectral shapes as do the spectra of X-rays associated with auroral kilometric radiation (AKR) events. For most of the high-latitude satellite passes when KC but no AKR was present, the X-ray energy spectra were harder than at times associated with AKR.

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On the origin of kilometric continuum

Cited by 34 publications

References 27 publications

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

Remote sensing of a NTC radio source from a Cluster tilted spacecraft pair

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

Observed X‐rays associated with kilometric continuum

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