Case studies on the wave propagation and polarization of ELF emissions observed by Freja around the local proton gyrofrequency

Santolı́k, O.; Parrot, M.

doi:10.1029/1998ja900045

Cited by 48 publications

(70 citation statements)

References 31 publications

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“…Other observations, which are consistent with the existence of diverging trajectories, are the measurements of ELF waves by Parrot (1999, 2000) on the lowaltitude satellite FREJA. As the satellite moved through the subauroral region from lower magnetic latitudes (MLAT), it observed that intense downgoing waves first had wave vectors inclined toward the equator.…”

Section: Discussion Observations and General Remarkssupporting

confidence: 57%

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

2005

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Abstract. We investigate the ray trajectories of nonductedly propagating lower-band chorus waves with respect to their initial angle θ 0 , between the wave vector and ambient magnetic field. Although we consider a wide range of initial angles θ 0 , in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ 0 , for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with θ 0 within an interval close to 0 • and on waves generated within an interval close to the Gendrin angle. We demonstrate that the ray trajectories of waves generated within an interval close to the Gendrin angle with a wave vector directed towards the lower L-shells (to the Earth) significantly diverge at the frequencies typical for the lower-band chorus. Some of these diverging trajectories reach the topside ionosphere having θ close to 0 • ; thus, a part of the energy may leak to the ground at higher altitudes where the field lines have a nearly vertical direction. The waves generated with different initial angles are reflected. A small variation of the initial wave normal angle thus very dramatically changes the behaviour of the resulting ray. Although our approach is rather theoretical, based on the ray tracing simulation, we show that the initial angle θ 0 of the waves reaching the ionosphere (possibly ground) is surprisingly close -differs just by several degrees from the initial angles which fits the observation of magnetospherically reflected chorus revealed by CLUSTER satellites. We also mention observations of diverging trajectories on low altitude satellites.

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Section: Discussion Observations and General Remarkssupporting

confidence: 57%

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

2005

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“…The direction of k can be obtained by consideringb and one component of the Fourier transform of the electric field,Ẽ 34 [Santolík and Parrot, 1999]. Such an analysis shows that k is parallel to V w 0 (t) and the whistler propagates along ÀB 0 , which is in agreement with how a right-hand polarised wave should propagate.…”

Section: The Normal To the Polarisation Planesupporting

confidence: 63%

Precession of the whistler polarisation plane normal observed on Freja

Karlsson

Carozzi

Bergman

et al. 2005

Geophysical Research Letters

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[1] We have observed that the normal to the polarisation plane of a whistler precesses around the geomagnetic field. Magnetic field observations by the Freja spacecraft have been used. These results were made possible by the use of an analysis which estimates the instantaneous polarisation properties of waves. During one event, the instantaneous normal of the polarisation plane precesses around the direction antiparallel to the geomagnetic field with an average deviation of 6°. In total, the normal precesses four times around this direction as the whistler frequency decreases from 2 to 0.4 kHz in about 0.2 s. Available theoretical understanding can not unambiguously explain the precession. We show that the precession of whistler wave vectors can be observed, and suggest to use this new observable parameter to put new constraints on the theories of whistler propagation. Citation: Karlsson, R. L., T.

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“…The determination of the wave vector direction is thus ambiguous. The complete wave vector direction without this ambiguity can be determined using both the magnetic field and the electric field (Lefeuvre et al, 1986-7;Santolík and Parrot, 1999). Having the magnetic field vector data and the two electric components, we use Eq.…”

Section: Analysis Methodsmentioning

confidence: 99%

Polarisation and propagation of lion roars in the dusk side magnetosheath

et al. 2001

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Abstract. We present observations of "lion roars" obtained in the magnetosheath by the Spectrum Analyser (SA) of the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment aboard Cluster. STAFF-SA calculates, in near real time, the complete auto-and cross-spectral matrix derived from three magnetic and two electric components of the electromagnetic field at 27 frequencies in the range of 8 Hz to 4 kHz. This allows the study of the properties of whistler mode waves and more particularly, the properties of "lion roars", which are intense, short-duration, narrowbanded packets of whistler waves. Their presence is favoured by the magnetic field troughs associated with mirror mode structures. During two short periods of well-defined mirror modes, we study the depth δB/B of the magnetic troughs, and the direction of propagation of the lion roars. During the first period, close to the magnetopause, deep magnetic troughs pass the satellites. Lion roars are then observed to propagate simultaneously in two directions, roughly parallel and anti-parallel to the magnetic field: this probably indicates that during this period, the satellites were within the successive source regions of lion roars. For the second period, far from the magnetopause, the magnetic troughs are less deep. Lion roars are propagating in only one direction, roughly anti-parallel to the magnetic field, suggesting that the source regions are more distant and predominantly on one side of the satellites.

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Case studies on the wave propagation and polarization of ELF emissions observed by Freja around the local proton gyrofrequency

Cited by 48 publications

References 31 publications

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

Precession of the whistler polarisation plane normal observed on Freja

Polarisation and propagation of lion roars in the dusk side magnetosheath

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