Long-period very low frequency emission pulsations

Carson, W. B.; Koch, Jean A.; Pope, J. H.; Gallet, Roger M.

doi:10.1029/jz070i017p04293

Cited by 50 publications

(32 citation statements)

References 17 publications

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“…These emissions, however, typically have frequencies of a few kilohertz, and they are right handed nearly circularly polarized [Němec et al, 2013b[Němec et al, , 2013c. Their modulation periods can range from some 10 s up to a couple of minutes [Carson et al, 1965;Smith et al, 1998], and they occur primarily on the dayside [Morrison et al, 1994;Engebretson et al, 2004;Hayosh et al, 2014]. The generation mechanism of these emissions is still not entirely understood.…”

Section: 1002/2014ja020816mentioning

confidence: 99%

Equatorial noise emissions with quasiperiodic modulation of wave intensity

et al. 2015

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Equatorial noise (EN) emissions are electromagnetic wave events at frequencies between the proton cyclotron frequency and the lower hybrid frequency observed in the equatorial region of the inner magnetosphere. They propagate nearly perpendicular to the ambient magnetic field, and they exhibit a harmonic line structure characteristic of the proton cyclotron frequency in the source region. However, they were generally believed to be continuous in time. We investigate more than 2000 EN events observed by the Spatio‐Temporal Analysis of Field Fluctuations and Wide‐Band Data Plasma Wave investigation instruments on board the Cluster spacecraft, and we show that this is not always the case. A clear quasiperiodic (QP) time modulation of the wave intensity is present in more than 5% of events. We perform a systematic analysis of these EN events with QP modulation of the wave intensity. Such events occur usually in the noon‐to‐dawn magnetic local time sector. Their occurrence seems to be related to the increased geomagnetic activity, and it is associated with the time intervals of enhanced solar wind flow speeds. The modulation period of these events is on the order of minutes. Compressional ULF magnetic field pulsations with periods about double the modulation periods of EN wave intensity and magnitudes on the order of a few tenths of nanotesla were identified in about 46% of events. We suggest that these compressional magnetic field pulsations might be responsible for the observed QP modulation of EN wave intensity, in analogy to formerly reported VLF whistler mode QP events.

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Section: 1002/2014ja020816mentioning

confidence: 99%

Equatorial noise emissions with quasiperiodic modulation of wave intensity

et al. 2015

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“…Quasiperiodic (QP) emissions are whistler mode plasma waves at frequencies between about 0.5 and 4 kHz observed in the inner magnetosphere both by ground-based and satellite instruments, which exhibit a nearly periodic modulation of the wave intensity. The period of the intensity modulation can range from some 10 s up to a couple of minutes [Carson et al, 1965;Sato and Kokubun, 1980;Sato and Fukunishi, 1981;Smith et al, 1998]. QP emissions occur primarily on the dayside [Morrison et al, 1994;Engebretson et al, 2004] and typically during geomagnetically rather quiet times [Hayosh et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Conjugate observations of quasiperiodic emissions by the Cluster, Van Allen Probes, and THEMIS spacecraft

et al. 2016

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We present results of a detailed analysis of two electromagnetic wave events observed in the inner magnetosphere at frequencies of a few kilohertz, which exhibit a quasiperiodic (QP) time modulation of the wave intensity. The events were observed by the Cluster and Van Allen Probes spacecraft and in one event also by the THEMIS E spacecraft. The spacecraft were significantly separated in magnetic local time, demonstrating a huge azimuthal extent of the events. Geomagnetic conditions at the times of the observations were very quiet, and the events occurred inside the plasmasphere. The modulation period observed by the Van Allen Probes and THEMIS E spacecraft (duskside) was in both events about twice larger than the modulation period observed by the Cluster spacecraft (dawnside). Moreover, individual QP elements occur about 15 s earlier on THEMIS E than on Van Allen Probes, which might be related to a finite propagation speed of a modulating ULF wave.

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“…Quasiperiodic (QP) emissions are whistler mode electromagnetic waves observed in the inner magnetosphere that exhibit a periodic time modulation of the wave intensity. The modulation periods can be from some 10 s up to a couple of minutes [Carson et al, 1965;Smith et al, 1998], and the events are primarily a dayside phenomenon [Morrison et al, 1994;Engebretson et al, 2004]. Using the ground-based measurements of the magnetic field, QP emissions are further classified as type 1 and type 2.…”

Section: Introductionmentioning

confidence: 99%

Multispacecraft Cluster observations of quasiperiodic emissions close to the geomagnetic equator

2014

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We present a detailed analysis of three electromagnetic wave events observed by the Cluster Wide‐Band Data instruments at frequencies of a few kilohertz, which exhibit a periodic time modulation of the wave intensity (quasiperiodic emissions). The events were measured when crossing the geomagnetic equator at radial distances of about 3–4 RE during the close separation campaign in July–October 2013. Coincident compressional magnetic field pulsations with the magnitude on the order of a few tenths of nanotesla were detected in two events. Their period corresponded to the modulation period of the quasiperiodic emissions in one event, while it was about double in the other. A possible explanation for this discrepancy between the two periods is given. Although Cluster 1, Cluster 3, and Cluster 4 were close to each other, Cluster 2 was located by more than 0.5 RE closer to the Earth. The same quasiperiodic modulation was observed by all Cluster spacecraft, but the emissions detected by Cluster 2 had a noticeable time delay. This can be explained by the wave propagation from the generation region located at larger radial distances, close to the plasmapause. The large range of L shells where the emissions are detected thus appears to be due to the unducted propagation from a spatially limited source. The frequency‐time structure of individual elements forming the events is evaluated, and it is shown that the time dependence of the intensity modulation can be approximated by a simple model.

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Long-period very low frequency emission pulsations

Cited by 50 publications

References 17 publications

Equatorial noise emissions with quasiperiodic modulation of wave intensity

Equatorial noise emissions with quasiperiodic modulation of wave intensity

Conjugate observations of quasiperiodic emissions by the Cluster, Van Allen Probes, and THEMIS spacecraft

Multispacecraft Cluster observations of quasiperiodic emissions close to the geomagnetic equator

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