Gyro line observations with the EISCAT VHF radar

Bjørnå, N.; Esjeholm, Bjørn Tore; Hansen, Truls Lynne

doi:10.1016/0021-9169(90)90046-p

Cited by 7 publications

(8 citation statements)

References 5 publications

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“…It cannot by any means enhance gyro lines to the level reported here, which is of orders of magnitude above the thermal level. Moderate enhancements at longer radar wavelengths (VHF) have been observed in earlier experiments (Bjørnat et al, 1990;.…”

Section: Frequency Offsetsmentioning

confidence: 81%

“…The thermal Landau damping of gyro lines increases with increasing aspect angle (Bjørnat et al, 1990). This means that it is more difficult to overcome the Landau damping and excite the line in the direction of scatter when the radar is pointing at 30°elevation than at lower elevations (see Fig.…”

Section: Other Characteristicsmentioning

confidence: 99%

“…Observations of gyro lines have been reported by Behnke and Hagen (1978) for the Arecibo (430-MHz) radar and by Bjørnat et al (1990) for the EISCAT VHF (224-MHz) radar. These observations were made under stable ionospheric conditions and the signal could be post-integrated over a long time; 1-2 h were necessary to see the line.…”

Section: Gyro Linesmentioning

confidence: 99%

“…Later Behnke and Hagen (1978) introduced the name 'whistler lines'. The name 'gyro lines' was introduced by Bjørnat et al (1990). Like the plasma-line resonance, the gyro-line resonance is predicted by cold plasma theory.…”

Section: Gyro Linesmentioning

confidence: 99%

“…We have post-integrated the 1989 and 1993 data over long time-periods looking for ordinary photoelectron enhanced gyro lines similar to those detected earlier by the EISCAT VHF radar (Bjørnat et al, 1990;. This was done for the whole height region covered by the experiment, but no lines were seen.…”

Section: Other Characteristicsmentioning

confidence: 99%

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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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Section: Frequency Offsetsmentioning

confidence: 81%

Section: Other Characteristicsmentioning

confidence: 99%

Section: Gyro Linesmentioning

confidence: 99%

Section: Gyro Linesmentioning

confidence: 99%

Section: Other Characteristicsmentioning

confidence: 99%

See 3 more Smart Citations

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

Malnes¹,

Bjørnå²,

Hansen³

1996

Ann. Geophys.

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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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Enhancement of incoherent scatter gyro lines by suprathermal electrons

Malnes

Bjørnå

1993

Journal of Atmospheric and Terrestrial Physics

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Gyro line observations with the EISCAT VHF radar

Cited by 7 publications

References 5 publications

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

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

On the theory of the incoherent scatter gyrolines

Enhancement of incoherent scatter gyro lines by suprathermal electrons

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