| 1. |
- DUBOULOZ, N, et al.
(författare)
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DETAILED ANALYSIS OF BROAD-BAND ELECTROSTATIC NOISE IN THE DAYSIDE AURORAL-ZONE
- 1991
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - SWEDISH INST SPACE PHYS,S-75590 UPPSALA,SWEDEN. ROYAL INST TECHNOL,S-10044 STOCKHOLM 70,SWEDEN.. - 0148-0227. ; 96:A3, s. 3565-3579
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Tidskriftsartikel (refereegranskat)abstract
- The great number of bursts of broadband electrostatic noise (BEN) recorded during crossings of the dayside auroral zone by the Viking satellite enables their statistical study. The angular distribution of BEN with respect to the Earth's magnetic field is shown to be most likely isotropic, implying that it cannot consist of a unique linear plasma mode. Most of the bursts evidence a power law spectrum from the lower hybrid and ion plasma frequencies up to frequencies sometimes much higher than the electron plasma frequency, suggesting the presence of nonlinear effects. This is confirmed by their high intensity, and by the correlation between their amplitude and their frequency extension. BEN emissions are associated with ion conical distributions and with field-aligned electron beams. Although most of the power is concentrated at very low frequencies and around the lower hybrid and ion plasma frequencies, electron acoustic and beam mode waves may contribute to the high-frequency extension of BEN. The most intense BEN emissions are also correlated with sharp cold plasma density gradients and probably involve drift instabilities. Strong quasi-static perpendicular electric fields, which induce high-speed plasma flows, are also measured, so that the Doppler effect may contribute to the broadening of the BEN spectrum.
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| 2. |
- HULTQVIST, B, et al.
(författare)
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ON THE UPWARD ACCELERATION OF ELECTRONS AND IONS BY LOW-FREQUENCY ELECTRIC-FIELD FLUCTUATIONS OBSERVED BY VIKING
- 1991
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Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS. - : American Geophysical Union (AGU). - 0148-0227. ; 96:A7, s. 11609-11615
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the generation of upward electron beams in the to side ionosphere on the amplitude of the slow electric field fluctuations and the magnitude of the dc potential difference in the acceleration region is found to agree with the model involving the fluctuating electric field component presented in 1988 by Hultqvist. The ratio between the amplitude of the electric field fluctuations, E(f), determined by the dipole electric field experiment, and the dc acceleration voltage V(acc), given by the energy of the upflowing ion beam, is much higher on average for satellite spins showing an upward electron beam than for the spins without. It is also shown that low plasma density favors the generation of electron beams.
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| 3. |
- MALINGRE, M, et al.
(författare)
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SPORADIC ELECTROMAGNETIC EMISSIONS IN THE AKR FREQUENCY-RANGE ASSOCIATED WITH ELECTROSTATIC PLASMA TURBULENCE
- 1992
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - : American Geophysical Union (AGU). - 0094-8276. ; 19:13, s. 1339-1342
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Tidskriftsartikel (refereegranskat)abstract
- We present heretofore unreported Viking observations of sporadic AKR bursts occurring well above the electron gyrofrequency together with spiky electrostatic emissions recorded just above the lower hybrid frequency, which exhibit a high degree of correlation in time. Both types of waves show simultaneous large amplitude variations of the order of 30-40 dB on time scales of a few hundreds of ms. Possible interpretations which may account for the observed correlation are investigated. Arguments are given which suggest that such events could be the signature of small scale non-linear structures in the plasma.
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| 4. |
- Mursula, Kalevi, et al.
(författare)
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Dispersive Pc1 bursts observed by Freja
- 1994
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 21:17, s. 1851-1854
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Tidskriftsartikel (refereegranskat)abstract
- Electric field measurements by the Freja double probe sensor are used to study equatorially generated ion cyclotron waves, also called Pc1 pulsations. We have examined the global occurrence and spectral properties of these waves in the upper ionosphere during 12-hour period on Nov. 18, 1992, when a long chain of structured Pc1 waves (pearls) was observed on ground. In agreement with ground observations, Pc1 waves were found to occur as short bursts of 10-25 s in early morning to postnoon MLT sector. Most Pc1 activity was detected within a small latitudinal range, extending from 60-degrees CGMlat at dawn to 630 CGMlat at noon. The latitudinal width of the source was only about 0.5-degrees CGMlat. Observations give evidence for a plasmapause connected source region that was several hours wide in MLT and active during many hours. One burst displayed a fully developed classical dispersive Pc1 pearl, now detected for the first time above the ionosphere. In all studied Pc1 events, two spectral maxima (bands) were observed. The longer Pc1 wave bursts showed evidence for a small time delay between the lower and upper frequency bands, unveiling a new dispersive phenomenon.
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