The upper- and lower-frequency cutoffs of magnetospherically reflected whistlers

Edgar, B. C.

doi:10.1029/ja081i001p00205

Cited by 79 publications

(81 citation statements)

References 12 publications

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“…For a discussion of the conditions required for ducted propagation, see Smith et al (1960) and Helliwell (1965). Most whistlers observed on the ground are believed to be caused by ducted propagation, whereas most whistlers observed via spacecraft are believed to be caused by nonducted propagation (Smith and Angerami, 1968;Edgar, 1976). Whistlers observed on the ground are primarily due to ducted propagation because a ducted whistler arrives in the opposite hemisphere with the wave vector nearly vertical, thereby allowing it to be transmitted through the ionosphere to the ground.…”

Section: Whistlersmentioning

confidence: 99%

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First results from the Cluster wideband plasma wave investigation

et al. 2001

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Abstract. In this report we present the first results from the Cluster wideband plasma wave investigation. The four Cluster spacecraft were successfully placed in closely spaced, high-inclination eccentric orbits around the Earth during two separate launches in July -August 2000. Each spacecraft includes a wideband plasma wave instrument designed to provide high-resolution electric and magnetic field waveforms via both stored data and direct downlinks to the NASA Deep Space Network. Results are presented for three commonly occurring magnetospheric plasma wave phenomena: (1) whistlers, (2) chorus, and (3) auroral kilometric radiation. Lightning-generated whistlers are frequently observed when the spacecraft is inside the plasmasphere. Usually the same whistler can be detected by all spacecraft, indicating that the whistler wave packet extends over a spatial dimension at least as large as the separation distances transverse to the magnetic field, which during these observations were a few hundred km. This is what would be expected for nonducted whistler propagation. No case has been found in which a strong whistler was detected at one spacecraft, with no signal at the other spacecraft, which would indicate ducted propagation. Whistler-mode chorus emissions are also observed in the inner region of the magnetosphere. In contrast to lightninggenerated whistlers, the individual chorus elements seldom show a one-to-one correspondence between the spacecraft, indicating that a typical chorus wave packet has dimensions transverse to the magnetic field of only a few hundred km or less. In one case where a good one-to-one correspondence existed, significant frequency variations were observed between the spacecraft, indicating that the frequency of the wave packet may be evolving as the wave propagates. Auroral kilometric radiation, which is an intense radio emission generated along the auroral field lines, is frequently observed over the polar regions. The frequency-time structure of this radiation usually shows a very good one-to-one correspondence between the various spacecraft. By using the Correspondence to: D. A. Gurnett (donald-gurnett@uiowa.edu) microsecond timing available at the NASA Deep Space Network, very-long-baseline radio astronomy techniques have been used to determine the source of the auroral kilometric radiation. One event analyzed using this technique shows a very good correspondence between the inferred source location, which is assumed to be at the electron cyclotron frequency, and a bright spot in the aurora along the magnetic field line through the source.

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Section: Whistlersmentioning

confidence: 99%

“…Typical whistler ducts are thought to have cross-sectional dimensions ranging from 50 to 500 km (Smith and Angerami, 1968). Although the dispersion properties of nonducted whistlers are somewhat different than ducted whistlers (Edgar, 1976), nose-like features, such as in Fig. 2, occur whenever a nonducted whistler has crossed the magnetic equator.…”

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confidence: 99%

First results from the Cluster wideband plasma wave investigation

et al. 2001

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“…They called this phenomenon Nu whistler and suggested its basic mechanism. According to these authors, the minimum frequency on a Nu-whistler spectrogram, where the two branches merge, corresponds to the wave that undergoes magnetospheric reflection at the observation point (see also Edgar, 1976). Magnetospheric reflection occurs when the waves reach some point where their frequency is less than the local lower-hybrid-resonance (LHR) frequency, so it is also referred to as LHR reflection.…”

Section: Introductionmentioning

confidence: 99%

Characteristic properties of Nu whistlers as inferred from observations and numerical modelling

2004

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Abstract. The properties of Nu whistlers are discussed in the light of observations by the MAGION 5 satellite, and of numerically simulated spectrograms of lightning-induced VLF emissions. The method of simulation is described in full. With the information from this numerical modelling, we distinguish the characteristics of the spectrograms that depend on the site of the lightning strokes from those that are determined mainly by the position of the satellite. Also, we identify the region in the magnetosphere where Nu whistlers are observed most often, and the geomagnetic conditions favouring their appearance. The relation between magnetospherically reflected (MR) whistlers and Nu whistlers is demonstrated by the gradual transformation of MR whistlers into Nu whistlers as the satellite moves from the high-altitude equatorial region to lower altitudes and higher latitudes. The magnetospheric reflection of nonducted whistler-mode waves, which is of decisive importance in the formation of Nu whistlers, is discussed in detail.

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“…As stated previously, the dispersion depends on several parameters, such as the intensity of the ambient magnetic field, the electron density, and the path length along the propagation paths. The path length between the source point of lightning strikes and the observation point in the Earth's plasmasphere affects the dispersion scale of lightning whistlers [9], [16]. Short path lengths lead to minimum dispersion, and vice versa [9], [16].…”

Section: Dispersion Analysismentioning

confidence: 99%

“…The path length between the source point of lightning strikes and the observation point in the Earth's plasmasphere affects the dispersion scale of lightning whistlers [9], [16]. Short path lengths lead to minimum dispersion, and vice versa [9], [16]. Furthermore, to estimate the path length, we can utilize a simple method by assuming that the structure of the Earth's magnetic field is approximated by a simple magnetic dipole model [17], [18].…”

Section: Dispersion Analysismentioning

confidence: 99%

Study of Dispersion of Lightning Whistlers Observed by Akebono Satellite in the Earth's Plasmasphere

Bayupati

Kasahara

Goto

2012

IEICE Trans. Commun.

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SUMMARYWhen the Akebono (EXOS-D) satellite passed through the plasmasphere, a series of lightning whistlers was observed by its analog wideband receiver (WBA). Recently, we developed an intelligent algorithm to detect lightning whistlers from WBA data. In this study, we analyzed two typical events representing the clear dispersion characteristics of lightning whistlers along the trajectory of Akebono. The event on March 20, 1991 was observed at latitudes ranging from 47.83 • (47,83 • N) to −11.09 • (11.09 • S) and altitudes between ∼2232 and ∼7537 km. The other event on July 12, 1989 was observed at latitudes from 34.94 • (34.94 • N) and −41.89 • (41.89 • S) and altitudes ∼1420-∼7911 km. These events show systematic trends; hence, we can easily determine whether the wave packets of lightning whistlers originated from lightning strikes in the northern or the southern hemispheres. Finally, we approximated the path lengths of these lightning whistlers from the source to the observation points along the Akebono trajectory. In the calculations, we assumed the dipole model as a geomagnetic field and two types of simple electron density profiles in which the electron density is inversely proportional to the cube of the geocentric distance. By scrutinizing the dipole model we propose some models of dispersion characteristic that proportional to the electron density. It was demonstrated that the dispersion D theoretically agrees with observed dispersion trend. While our current estimation is simple, it shows that the difference between our estimation and observation data is mainly due to the electron density profile. Furthermore, the dispersion analysis of lightning whistlers is a useful technique for reconstructing the electron density profile in the Earth's plasmasphere.

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The upper- and lower-frequency cutoffs of magnetospherically reflected whistlers

Cited by 79 publications

References 12 publications

First results from the Cluster wideband plasma wave investigation

First results from the Cluster wideband plasma wave investigation

Characteristic properties of Nu whistlers as inferred from observations and numerical modelling

Study of Dispersion of Lightning Whistlers Observed by Akebono Satellite in the Earth's Plasmasphere

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