Influence of Electrostatic Electron Waves on the Incoherent Scattering Cross-section

Trulsen, J.; Bjørnå, N.

doi:10.1088/0031-8949/17/1/003

Cited by 17 publications

(18 citation statements)

References 11 publications

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“…[13] We should note that there has been some work suggesting that gyro lines could be enhanced by photoelectrons [e.g., Trulsen and Bjorna, 1978;Malnes and Bjorna, 1993]. The data presented in this paper, and evidence for the fact that the gyro line appears after sunset discussed already, imply that no enhancement exists for these observations.…”

Section: Resultsmentioning

confidence: 64%

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Diurnal variability of the gyro resonance line observed with the Arecibo incoherent scatter radar at E‐ and F1‐region altitudes

Janches

Nicolls

2007

Geophysical Research Letters

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[1] In this paper, we report on observations of the diurnal variation of a resonance line that occurs near the gyro frequency as seen with the incoherent scatter radar (ISR) at the Arecibo Observatory. This gyro resonance line has rarely been observed in ISR data, but recent results, exemplified by the observations of Bhatt et al. (2006), have implied that the gyro line is a common ionospheric feature. The observations presented here were made with much better altitude resolution in comparison with previous results and represent full 24 hour coverage for several days. The data indicate that an increase in the gyro line intensity near sunrise and sunset is an everyday occurrence. As the increase in intensity is occurring at sunset, the gyro line frequency drops from the expected frequency to one near zero frequency. As the increase in intensity is occurring at sunrise, the gyro line frequency increases from near zero frequency to one near the expected gyro line frequency. This behavior of the gyro line frequency and intensity has not been observed before. We explain these results using normal Maxwellian incoherent scatter theory together with the diurnal variation of the density in the E and F1 regions. These results may explain previous observations of the gyro line made at Arecibo and suggest avenues of future research for studying this exciting feature of the incoherent scatter spectrum. Citation: Janches, D., and M. J. Nicolls (2007), Diurnal variability of the gyro resonance line observed with the Arecibo incoherent scatter radar at E-and F1-region altitudes,

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Section: Resultsmentioning

confidence: 64%

“…This electron gyro resonance line, whose name was coined by Bjorna et al [1990], corresponds to the high frequency end of the whistler mode, which approaches the lower hybrid mode for oscillations perpendicular to the magnetic field. The frequency of the line corresponds to approximately [Trulsen and Bjorna, 1978;Shume, 2000] …”

Section: Introductionmentioning

confidence: 99%

Diurnal variability of the gyro resonance line observed with the Arecibo incoherent scatter radar at E‐ and F1‐region altitudes

Janches

Nicolls

2007

Geophysical Research Letters

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“…which is the estimate for the real part of the frequency presented by Trulsen and Bjørna [1978]. We need only to verify that the n ≠ 0 terms do not contribute significantly to equation (1).…”

Section: Popular Theorymentioning

confidence: 95%

“…Next, a factor of 2 r can be subtracted from each side of equation (11), and with the approximation r ≈ Ω cos , the imaginary part of the frequency found by Trulsen and Bjørna [1978] can be derived: (9) in the text. The abscissa for the figure is the square root of the parameter r = k 2 v 2 t ∕Ω 2 .…”

Section: Popular Theorymentioning

confidence: 99%

“…The theory most often cited to predict the frequency of gyrolines in ISR observations is that of Trulsen and Bjørna [1978] and works derived from it. The Trulsen and Bjørna [1978] paper itself provides few details about the theoretical derivation but references a pair of technical reports that are not widely available Trulsen, 1976a, 1976b].…”

Section: Introductionmentioning

confidence: 99%

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On the theory of the incoherent scatter gyrolines

2017

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The incoherent scatter spectrum feature referred to as the “gyroline” is investigated theoretically and experimentally. The gyroline is associated with the dispersion relation for electrostatic whistler waves. Earlier treatments by Trulsen and Bjørna (1978, and references therein) derive the frequency and growth rate for these waves, but their derivation is only accurate for very small magnetic aspect angles, i.e., for wave vectors close to perpendicular to the geomagnetic field. Their expression for the frequency has the form of a low‐order Padé approximate, but we find that a simple formula of this kind accurate for arbitrary magnetic aspect angles does not exist. We therefore analyze the incoherent scatter gyroline feature computationally. The analysis is supported by range‐resolved incoherent scatter spectrograms measured recently at Arecibo. The gyroline feature is shown to be strongest in the midlatitude E and valley regions where the electron temperature is low enough to avoid cyclotron damping.

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Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude

Malnes¹,

Bjørnå²,

Hansen³

1996

Ann. Geophys.

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Abstract. We have observed a number of strong echoes with the European incoherent-scatter (EISCAT) UHF (930-MHz) radar at angles 83.5°and 78.6°with the geomagnetic field and at about 100-km altitude north in the auroral zone. The echoes are shortlived and occur in single 2-or 10-s data dumps. They are offset by 125-130 kHz with respect to the transmitted frequency. In most cases the offset compares well with the frequency of gyro lines in the incoherent-scatter spectrum, as given by the standard linear dispersion relation. But sometimes the measured offsets deviate significantly from the model calculations, and the interpretation in terms of gyro lines becomes questionable. The discrepancy could possibly be explained by local deviations in the magnetic field from the model (IGRF 1987), which are generated by incoming particle beams. A more serious problem with the gyro-line theory is how the line can be excited at altitudes where the collisional damping is substantial. The high intensity and short lifetime of the signal point to a fast-growing plasma instability as the likely excitation mechanism, if the gyroline interpretation is correct. The cause of the instability could be the same particle beams as those causing the disturbances in the magnetic field. Alternatively, the observations may be interpreted as meteor head echoes. The large Doppler shifts, the short lifetimes and the altitudes of the signals support this explanation. The main difficulty is that the distribution of measured offsets appears to be different in magnetically active conditions and in less active conditions. Also, the occurrence of echoes does not seem to follow the expected changes in meteor density. More observations in different conditions are needed to decide between the two interpretations. As it is, we are inclined to believe in the meteor head echo theory, the objections to the gyro-line theory being more fundamental.

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Influence of Electrostatic Electron Waves on the Incoherent Scattering Cross-section

Cited by 17 publications

References 11 publications

Diurnal variability of the gyro resonance line observed with the Arecibo incoherent scatter radar at E‐ and F1‐region altitudes

Diurnal variability of the gyro resonance line observed with the Arecibo incoherent scatter radar at E‐ and F1‐region altitudes

On the theory of the incoherent scatter gyrolines

Anomalous echoes observed with the EISCAT UHF radar at 100-km altitude

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