Generation of ordinary mode auroral kilometric radiation from extraordinary mode waves

Hayes, L. M.; Melrose, D. B.

doi:10.1029/ja091ia01p00211

Cited by 15 publications

(11 citation statements)

References 20 publications

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“…Simulations by Pritchett and Strangeway [1985] suggest that a relativistic effect coupling X mode (perpendicular) electric fields into parallel (O mode) fields may account for the observed LO to RX mode intensity ratios. The LO mode may also be created from conversion of RX mode emission by polarization mismatch in regions of high‐density gradients [ Hayes and Melrose , 1986; Louarn and Le Quéau , 1996a].…”

Section: Growth Rates: Parameter Searchmentioning

confidence: 99%

“…When LO and RX mode are seen together, their observed fluxes are often highly correlated, with LO mode flux densities about 2% of RX mode [ Mellott et al , 1984]. This suggests that LO mode could result from mode conversion of RX mode radiation, perhaps by reflection at sharp density boundaries [ Calvert , 1982; Hayes and Melrose , 1986]. More recently, Hanasz et al [2003] reported that LO mode AKR is detected much more often at low magnetic latitudes ( λ m ∼ 60°) in the afternoon auroral sector compared with the evening sector.…”

Section: Introductionmentioning

confidence: 99%

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Dependence of cyclotron maser instability growth rates on electron velocity distributions and perturbation by solitary waves

et al. 2007

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[1] We calculate growth rates and corresponding gains for right-hand circularly polarized extraordinary (RX) and left-hand ordinary circularly polarized (LO) mode radiation associated with the cyclotron maser instability (CMI) for parameterized horseshoe electron velocity distributions. The velocity distribution function was modeled to closely fit the electron distribution functions observed in the auroral cavity. We systematically varied the model parameters as well as the propagation direction to study the dependence of growth rates on model parameters. The growth rate depends strongly on loss cone opening angle, which must be less than 90°for significant CMI growth. The growth rate is sharply peaked for perpendicular radiation (k k = 0), with a full width at half maximum 1.7°, in good agreement with observed k-vector orientations and numerical simulations. The fractional bandwidth varied between 10 À4 and 10 À2 , depending most strongly on propagation direction. This range encompasses nearly all observed fractional auroral kilometric radiation (AKR) burst bandwidths. We find excellent agreement between the computed RX mode emergent intensities and observed AKR intensities assuming convective growth length L c % 20-40 km and group speed 0.15c. The only computed LO mode growth rates compatible observed LO mode radiation levels occurred for number densities more than 100 times the average energetic electron densities measured in auroral cavities. This implies that LO mode radiation is not produced directly by the CMI mechanism but more likely results from mode conversion of RX mode radiation. We find that perturbation of the model velocity distribution by large ion solitary waves (ion holes) can enhance the growth rate by a factor of 2-4. This will result in a gain enhancement more than 40 dB depending on the convective growth length within the structure. Similar enhancements may be caused by strong electromagnetic ion cyclotron waves.

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Section: Growth Rates: Parameter Searchmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dependence of cyclotron maser instability growth rates on electron velocity distributions and perturbation by solitary waves

et al. 2007

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“…The L ‐ O mode AKR can be emitted by the electron‐cyclotron maser due to two reasons, either in a direct generation of the O mode within a source of a sufficiently large electron density, when a ratio of plasma to gyro‐frequency f pe / f ce ≥ 0.3 [ Benson , 1985; Benson et al , 1988], or in a partial mode conversion from the X mode to the O mode due to a polarization mismatch for the waves escaping through the density gradient at the source boundary [ Calvert , 1982; Hayes and Melrose , 1986; Louarn and Le Quéau , 1996]. Thus it can be expected that the L ‐ O mode will occur and sometimes dominate in regions of larger density, either inside the source cavities or in the ambient plasma, and the R ‐ X mode will dominate in regions of lower density.…”

Section: Introductionmentioning

confidence: 99%

Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes

et al. 2003

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[1] Occurrence distributions of the auroral kilometric radiation (AKR) and its right-hand extraordinary (R-X ) and left-hand ordinary (L-O) wave modes are determined from polarization measurements on Interball-2 (Auroral). The AKR is much less frequent on the dayside (20% of the observing time) than on the nightside (70%). A bulk of its occurrence extends from invariant latitude of 80 at afternoon hours of MLT to 60 at night hours. Like the nightside AKR, the dayside one is generated through the electron-cyclotron maser instability. This is concluded from domination of the R-X mode on the dayside similarly to the nightside. On the dayside the L-O mode of AKR is roughly three times more frequent (30% of the AKR time) than that on the nightside (10%). At afternoon hours the L-O occurs more frequently at lower invariant latitudes. This is explained by propagation of the L-O mode from nightside sources far beyond the ''horizon'' of the R-X mode. We find two classes of the circular polarization spectra: ''regular,'' with the dominating R-X mode observed in the upper part of the AKR frequency spectrum and the weak L-O mode in its lower part, and patchy ''irregular,'' with different polarizations interwoven randomly over the whole frequency range of AKR. For ''regular'' spectra the L-O/R-X power ratios are between 0.2 and 0.002. For the ''irregular'' ones they are between 1 and 0.01. The ''irregular'' spectra, reported for the first time, are interpreted as due to irregular refraction of the R-X rays on the plasma density fluctuations near the nightside sources. We show also evidence of another component of the AKR observed on the dayside, which arrives from directions of possible dayside sources likely related to the cusp or the low-latitude boundary layers.INDEX TERMS: 2704 Magnetospheric Physics: Auroral phenomena (2407); 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 6964 Radio Science: Radio wave propagation; 6939 Radio Science: Magnetospheric physics; KEYWORDS: antennas, auroral phenomena, radio wave propagation, wave in plasma, auroral kilometric radiation Citation: Hanasz, J., M. Panchenko, H. de Feraudy, R. Schreiber, and M. M. Mogilevsky, Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes,

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“…Major theoretical efforts have been directed toward explaining the fine structure of the R-X mode I- Calvert, 1982;Melrose, 1986]. In order to get L-O mode AKR from low-density source regions, R-X to L-O mode conversion at density boundaries was suggested by Calvert ['1982] and investigated in detail by Hayes and Melrose ['1986]. Ordinary mode generation based on Z to L-O mode wave conversion has also been proposed [Benson, 1975;Jones, 1977 [1986] also support the by-product mechanism because the fundamental R-X mode, being generated near a cutoff conditions, would be expected to be refracted into a different final direction.…”

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confidence: 99%

Ordinary mode auroral kilometric radiation fine structure observed by DE 1

Benson¹,

Mellott²,

Huff³

et al. 1988

J. Geophys. Res.

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The fine structure observed with intense right‐hand extraordinary (R‐X) mode auroral kilometric radiation (AKR) has received major theoretical attention. Data from the Dynamics Explorer 1 plasma wave instrument indicate that left‐hand ordinary (L‐O) mode AKR possesses similar fine structure. Several theories have been proposed to explain the fine structure of the R‐X mode AKR. In order to account for the L‐O mode fine structure, these theories will have to be modified to produce the L‐O mode directly or will have to rely on mode conversion processes from the R‐X to the L‐O mode.

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Generation of ordinary mode auroral kilometric radiation from extraordinary mode waves

Cited by 15 publications

References 20 publications

Dependence of cyclotron maser instability growth rates on electron velocity distributions and perturbation by solitary waves

Dependence of cyclotron maser instability growth rates on electron velocity distributions and perturbation by solitary waves

Occurrence distributions of the auroral kilometric radiation ordinary and extraordinary wave modes

Ordinary mode auroral kilometric radiation fine structure observed by DE 1

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