HF radar observations of decaying artificial field‐aligned irregularities

Hysell, D. L.; Kelley, M. C.; Yampolski, Yu. M.; Beley, V. S.; Koloskov, A. V.; Ponomarenko, P. V.; Tyrnov, O. F.

doi:10.1029/96ja02647

Cited by 32 publications

(36 citation statements)

References 23 publications

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“…However, estimates of the plasma diffusion coefficient, D 100−200 m 2 /s, derived from the measured spectral width values, were much larger than typical values for the ambipolar diffusion coefficient in the F-region, which are D∼1 m 2 /s (e.g. Hysell et al, 1996). André et al (2000) discussed Bohm diffusion as a possible alternative to the classical mechanism.…”

Section: Introductionmentioning

confidence: 95%

Spectral width of SuperDARN echoes: measurement, use and physical interpretation

Ponomarenko

Waters

2006

Ann. Geophys.

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Abstract. The Doppler velocity and spectral width are two important parameters derived from coherent scatter radar systems. The Super Dual Auroral Radar Network (Super-DARN) is capable of monitoring most of the high latitude region where different boundaries of the magnetosphere map to the ionosphere. In the past, the spectral width, calculated from SuperDARN data, has been used to identify the ionosphere footprints of various magnetosphere boundaries. In this paper we examine the way the spectral width is presently estimated from the radar data and describe several recommendations for improving the algorithm. Using the improved algorithm, we show that typical spectral width values reported in the literature are most probably overestimated. The physical interpretation of the cause of various magnitudes of the spectral width is explored in terms of the diffusion and dynamics of ionospheric plasma irregularities.

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Section: Introductionmentioning

confidence: 95%

Spectral width of SuperDARN echoes: measurement, use and physical interpretation

Ponomarenko

Waters

2006

Ann. Geophys.

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“…The Bragg scale range for SuperDARN frequencies is 10−15 m. For the magnetised plasma in the F-region, irregularities at these sizes are highly anisotropic and aligned with the geomagnetic field lines due to the large difference between the ambipolar plasma diffusion coefficients along and across B 0 (see e.g. Hysell et al, 1996). The effective scattering cross-section of these irregularities depends on their intensity, shape and orientation with respect to the incident wave propagation direction (Booker, 1956;Walker et al, 1987),…”

Section: Modelling Hf Backscatter Characteristicsmentioning

confidence: 99%

Refractive index effects on the scatter volume location and Doppler velocity estimates of ionospheric HF backscatter echoes

et al. 2009

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Abstract. Ionospheric E × B plasma drift velocities derived from the Super Dual Auroral Radar Network (SuperDARN) Doppler data exhibit systematically smaller (by 20-30%) magnitudes than those measured by the Defence Meteorological Satellites Program (DMSP) satellites. A part of the disagreement was previously attributed to the change in the E/B ratio due to the altitude difference between the satellite orbit and the location of the effective scatter volume for the radar signals. Another important factor arises from the freespace propagation assumption used in converting the measured Doppler frequency shift into the line-of-sight velocity. In this work, we have applied numerical ray-tracing to identify the location of the effective scattering volume of the ionosphere and to estimate the ionospheric refractive index. The simulations show that the major contribution to the radar echoes should be provided by the Pedersen and/or escaping rays that are scattered in the vicinity of the F-layer maximum. This conclusion is supported by a statistical analysis of the experimental elevation angle data, which have a signature consistent with scattering from the F-region peak. A detailed analysis of the simulations has allowed us to propose a simple velocity correction procedure, which we have successfully tested against the SuperDARN/DMSP comparison data set.

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“…In conjunction with these experiments, a second group of American and Ukrainian scientists at Kharkov, Ukraine monitored the effects of ionospheric heating over SURA using bistatic HF radar scatter from field-aligned irregularities (FAT) [Hysell et al, 1996]. These measurements provided a record of the amplitude and time history of scattered radio waves from FAT over SURA.…”

Section: Tionsmentioning

confidence: 99%

Effect of ionospheric self‐conditioning and preconditioning on the broad upshifted maximum component of stimulated electromagnetic emission

Wagner¹,

Bernhardt²,

Goldstein³

et al. 1999

J. Geophys. Res.

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Abstract. Stimulated electromagnetic emissions (SEE) are high-frequency radio emissions that are generated during high-power, high-frequency, ordinary mode (O-mode), radiowave heating of the ionosphere. These emissions are particularly useful in ionospheric heating experiments because they provide a way of monitoring space plasma processes remotely and passively. In order to utilize these emissions for diagnostic purposes, it is necessary to understand the space plasma processes involved in their generation. The purpose of these experiments was to observe the responses of a particular component of the SEE, the broad upshifted maximum (BUM), to a variety of heating stimuli in an effort to understand the factors involved in its development. Heating experiments were conducted at the Radiophysical Research Institute SURA Ionospheric Modification Facility in Russia. Experiments consisted of single-pump, two-pump, and single-pump power-stepping experiments. The single-pump and two-pump transmissions were organized into groups of pulses of varying widths and spacings to facilitate the investigation of self-conditioning, preconditioning, and two-pump-interaction conditioning effects. The major findings of these experiments are that the action of a pump can have a conditioning effect on the medium that affects the time development of the BUM. The result of the conditioning process is the formation of an overshoot in the temporal development of the BUM. A residual conditioning effect is sustained after the end of a pump pulse for a period of time (-30 s). The residual conditioning acts as preconditioning for the BUM of a subsequent pump pulse. A second O-mode pump (pump2), at a frequency a few hundred kilohertz above that of the first pump (pump 1), is observed to cause additional suppression of the pumpl BUM, implying an enhanced conditioning effect. Time constants for the buildup and decay of the conditioning effects are estimated. During power-stepping experiments, the BUM spectrum was observed to evolve from a weak, narrow spectrum at an effective radiated power (ERP) of •5 MW, to a strong, broad spectrum with a ramp-like spectral tail at an ERP of •150 MW. Other features noted during power stepping include (1) strong BUM transients at pump power level transitions, (2) BUM amplitude asymmetry between power-up and power-down sides of a power stepping cycle, (3) reduction of the BUM spectral peak offset from the pump frequency with increasing pump power, and (4) power law dependence of BUM power on pump power (exponent -2). Results of these experiments are used in an attempt to assess the relevance of small-scale irregularity generation and electron heating mechanisms to the observed conditioning effects. IntroductionStimulated electromagnetic emissions (SEE) are highfrequency (HF) radio emissions that are generated as a result of a complicated series of interactions between a high-power, ordinary mode (O-mode), HF radiowave pump (the heater), and internal plasma waves in the ionized upper atmosphere.•Now at Laurel, Mar...

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HF radar observations of decaying artificial field‐aligned irregularities

Cited by 32 publications

References 23 publications

Spectral width of SuperDARN echoes: measurement, use and physical interpretation

Spectral width of SuperDARN echoes: measurement, use and physical interpretation

Refractive index effects on the scatter volume location and Doppler velocity estimates of ionospheric HF backscatter echoes

Effect of ionospheric self‐conditioning and preconditioning on the broad upshifted maximum component of stimulated electromagnetic emission

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