Magnetospheric plasma wave research 1975–1978

Shawhan, S. D.

doi:10.1029/rg017i004p00705

Cited by 57 publications

(12 citation statements)

References 306 publications

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“…Thus, our observation result of the 3 f ce roar supports this proposed generation mechanism. It is well known that high-temperature anisotropy of the suprathermal electrons in plasma medium results in intense plasma instability, and it is further intensified when the upper hybrid frequency matches the harmonics of the electron cyclotron frequency (Shawhan, 1979). In the MF burst event observed on September 23, 2006, the auroral breakup occurred about 1 min after the termination of the MF burst.…”

Section: Discussionmentioning

confidence: 99%

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

et al. 2008

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In order to study the generation and propagation processes of MF auroral radio emissions (referred to as auroral roar and MF burst) in the polar ionosphere, an Auroral Radio Spectrograph (ARS) system was installed at Husafell station in Iceland (invariant latitude: 65.3• ). Data analysis of man-made transmissions also provides useful information for the ionosphere study as well as an investigation of auroral radio emissions since the propagation character of MF radio waves changes depending on electron-neutral collisions in the bottomside ionosphere. Thus, ionospheric absorption is examined in comparison with the solar zenith angle and auroral phenomena. The results indicate that the ARS data can be used to detect ionization occurring at distant regions. In late 2006, the ARS detected one auroral roar and two MF bursts, which were identified as left-handed polarized waves. Results of data analysis, including other auroral data and particle spectra observed by the DMSP satellite, suggest that the MF bursts are generated by electrons with an average energy of several keV associated with auroral breakup. On the other hand, the auroral roar is generated as upper hybrid waves by relatively low-energy electrons over the observation site and propagates downward, being converted into L-O mode electromagnetic waves.

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Section: Discussionmentioning

confidence: 99%

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

et al. 2008

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“…Electrons originally trapped in the magnetic field of the earth may thus diffuse into the loss cone and precipitate into the ionosphere. Simultaneous ground-based measurements of auroral emission intensities from the ionosphere and conjugate measurements of wave and particle characteristics in the equatorial plane are needed to confirm the influence of whistler mode waves on particle diffusion and has most recently been reported by Shepherd et al [1980] using the GEOS 2 satellite (for a review on wave-particle interactions in the magnetosphere see Fredricks [1975], Gendrin [1975], and Shawhan [1979]).…”

Section: Introductionmentioning

confidence: 99%

Observations on the GEOS 1 satellite of whistler mode signals transmitted by the Omega Navigation System Transmitter in northern Norway

Neubert¹,

Ungstrup²,

Bahnsen³

1983

J. Geophys. Res.

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Whistler mode signals of 0.9–1.1 s duration at 10.2, 11.33, and 13.6 kHz launched by the Omega Navigation System transmitter located in northern Norway have been observed on GEOS 1. The signals were observed both inside and outside the plasmasphere in two regions of the magnetosphere, in December 1977 at 10–20° north of the equator on the morningside and in May 1978 10° south of the equator on the nightside. For a sequence of particularly strong pulses in the December period, the ‘instantaneous’ wave normal directions were calculated and found to have angles of 120–140° to the magnetic field of the earth pointing 0–40° eastward. These pulses have amplitudes of the order of 10 μV/m and refractive indices above 30. At times the amplitude envelope of the signals is unmodulated, but often the amplitude and the wave normal direction are strongly modulated on a time scale of 0.2 s. We attribute these features to ray path mixing. The signals are often prolonged up to 1 s, which is interpreted as an overlap of the primary pulse with the echo of the pulse reflected from the topside ionosphere in the southern hemisphere. While the signals do not trigger strong emissions, we do observe ∼0.1‐s long bursts at the tail of some direct pulses.

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“…The satellite altitudes when these three saucers were observed were about 2540 km and 2530 and 1960 km, respectively. On the basis of the foregoing information most authors [e.g., Shawhan, 1979; Copyright 1982 by the American Geophysical Union.…”

Section: Introductionmentioning

confidence: 99%

Source regions deduced from attenuation bands in VLF saucers

Horita¹,

James²

1982

J. Geophys. Res.

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Fourteen VLF saucer events exhibiting attenuation bands related to the proton gyrofrequency were studied to check the usual assumption that saucers are due to upgoing whistler mode waves. It was found that most of the 14 saucers exhibited attenuation bands with proton gyrofrequencies smaller than the local proton gyrofrequency at the satellite. Assuming that the generation or interaction region with its characteristic proton gyrofrequency imprints its signature on the saucers originating at or propagating through that location, these observations suggest that the majority of the 14 saucer waves propagated down to the ISIS 2 satellite. The generation/interaction regions of these saucers exhibiting attenuation bands were also found to be located in the 2300–0100 local time sector between 60° and 70° geomagnetic latitude, with a tendency to be at lower latitudes for higher geomagnetic activity. Although the attenuation bands are usually horizontal, a new observation is the positively sloping attenuation bands, suggesting larger proton gyrofrequency values with time. When combined with already published data on particle precipitation, these observations imply that downgoing suprathermal electrons are also responsible for saucers.

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Magnetospheric plasma wave research 1975–1978

Cited by 57 publications

References 306 publications

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

Auroral radio emission and absorption of medium frequency radio waves observed in Iceland

Observations on the GEOS 1 satellite of whistler mode signals transmitted by the Omega Navigation System Transmitter in northern Norway

Source regions deduced from attenuation bands in VLF saucers

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