A comparison of EISCAT and SuperDARN <i>F</i>‐region measurements with consideration of the refractive index in the scattering volume

Gillies, R. G.; Hussey, G. C.; Sofko, G. J.; Wright, D. M.; Davies, J. A.

doi:10.1029/2009ja014694

Cited by 24 publications

(53 citation statements)

References 31 publications

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“…Previous attempts to model the refractive index using electron density estimates or elevation angle measurements have showed significant improvement, but have not been completely successful. It was proposed by Gillies et al [2010a] that smallscale dense structures are dominant in the scattering process. In turn, these structures with enhanced electron densities cause the refractive index in the scattering volume to be much lower than the current estimates predict.…”

Section: Scattering Volume Plasma Frequency From Frequency Shiftsmentioning

confidence: 99%

“…[29] The study by Gillies et al [2010a] attributed lower than average SuperDARN velocities to the existence of small-scale highly dense structures in the SuperDARN scattering volume. It is reasonable to expect that coherent backscatter which is detected by SuperDARN only occurs in relatively small portions of a larger SuperDARN range cell.…”

Section: Comparisons To Irimentioning

confidence: 99%

“…Other structures which may provide locations for HF coherent radar scatter are the midlatitude trough [Moffett and Quegan, 1983] and traveling ionospheric disturbances (TIDs) [e.g., Pryse et al, 1995]. A more detailed description of these possible smallscale structures and their importance to SuperDARN coherent scatter may be found by Gillies et al [2010a].…”

Section: Comparisons To Irimentioning

confidence: 99%

“…[6] Another comparison of SuperDARN velocities with velocities measured by the European Incoherent Scatter (EISCAT) radar was performed by Gillies et al [2010a]. This study compared velocities measured by the Hankasalmi SuperDARN and tristatic velocities measured by EISCAT from 1995-1999.…”

Section: Introductionmentioning

confidence: 99%

“…[7] It was suggested by Gillies et al [2010a] that the reason for lower SuperDARN velocities (even after attempting to account for refractive index) was that SuperDARN scatter would tend to occur most strongly in the regions of highestelectron density. It is reasonable to assume that, although scatter will occur throughout a SuperDARN range cell (which is 45 km in range, ∼50 km in width, and up to several hundred kilometers in altitude), the strongest scatter occurs in only small regions (∼hundreds of meters) of the cell.…”

Section: Introductionmentioning

confidence: 99%

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Improvement of HF coherent radar line-of-sight velocities by estimating the refractive index in the scattering volume using radar frequency shifting

et al. 2011

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[1] Measurements of ionospheric drift velocities using HF coherent scatter radars, such as SuperDARN, are generally underestimated because the refractive index in the scattering volume has not been taken into account. Refractive index values evaluated from electron density measurements, international reference ionosphere predictions, or elevation angle measurements have been applied to SuperDARN velocities in past studies. However, the SuperDARN velocities so obtained were, on average, statistically lower than velocities measured by other instruments. One possible explanation for this underestimation is that HF coherent scatter preferentially occurs in regions of the ionosphere where the scattering cross section is largest, and such regions are characterized by small-scale structures which have higher-than-average electron densities. This was not accounted for in past studies because the refractive index estimates used were from large scale and therefore smoothed estimates of electron density. In this paper, a new method of estimating the actual electron density (or plasma frequency) at the location of SuperDARN scatter (instead of the larger-scale background electron density) is presented. This method takes advantage of the frequency shifts which occur in normal SuperDARN operations. If it is assumed that, on average, the actual ionospheric drift velocity and plasma frequency are roughly constant before and after a shift in frequency, any change in measured velocity as SuperDARN changes frequency is due to a change in refractive index. An analysis of the change in the measured velocity resulting from each shift in frequency gives an experimentally based estimate of the electron density in the scattering volume. A statistical analysis of essentially all frequency shifts by SuperDARN and the estimated electron densities in the scattering volume has been performed. The resulting electron densities are appreciably higher than previous methods to estimate electron density predict. Application of this new method to velocity comparisons between SuperDARN and other instruments results in agreement between the HF radar and non-HF radar velocities for the first time. This new method allows for the first direct measurements of electron densities in the exact locations where the cross section for SuperDARN scatter maximizes.

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Section: Scattering Volume Plasma Frequency From Frequency Shiftsmentioning

confidence: 99%

Section: Comparisons To Irimentioning

confidence: 99%

Section: Comparisons To Irimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Improvement of HF coherent radar line-of-sight velocities by estimating the refractive index in the scattering volume using radar frequency shifting

et al. 2011

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Temporal and spatial resolved SuperDARN line of sight velocity measurements corrected for plasma index of refraction using Bayesian inference

2015

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Recent work by Gillies et al. (2012Gillies et al. ( , 2009Gillies et al. ( , 2010 has sought an explanation for the SuperDARN line-of-sight velocity underestimate of ionospheric plasma velocity. The reason for the underestimation is thought to be from the modification of the measured Doppler shift of the backscattered signal due to phase refractive index of the ionospheric plasma in the scattering region. Presented here is an analysis technique to estimate the plasma drift velocity, correcting for the index of the refraction of the scattering medium. The technique requires dual frequency SuperDARN observations and calculates velocity from the phase of the SuperDARN autocorrelation function (ACF). Both plasma velocity and plasma density are treated as independent unknowns, and self-consistent error estimates are generated for each. This new technique was employed at the McMurdo radar, resulting in estimates of plasma velocity on scales relevant to existing SuperDARN data products. The McMurdo dual frequency analysis also provides a new SuperDARN data product, an estimate for the plasma density in the ionospheric region derived wholly from SuperDARN backscatter.

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Ionospheric electron number densities from CUTLASS dual‐frequency velocity measurements using artificial backscatter over EISCAT

et al. 2016

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Using quasi‐simultaneous line‐of‐sight velocity measurements at multiple frequencies from the Hankasalmi Cooperative UK Twin Auroral Sounding System (CUTLASS) on the Super Dual Auroral Radar Network (SuperDARN), we calculate electron number densities using a derivation outlined in Gillies et al. (2010, 2012). Backscatter targets were generated using the European Incoherent Scatter (EISCAT) ionospheric modification facility at Tromsø, Norway. We use two methods on two case studies. The first approach is to use the dual‐frequency capability on CUTLASS and compare line‐of‐sight velocities between frequencies with a MHz or greater difference. The other method used the kHz frequency shifts automatically made by the SuperDARN radar during routine operations. Using ray tracing to obtain the approximate altitude of the backscatter, we demonstrate that for both methods, SuperDARN significantly overestimates Ne compared to those obtained from the EISCAT incoherent scatter radar over the same time period. The discrepancy between the Ne measurements of both radars may be largely due to SuperDARN sensitivity to backscatter produced by localized density irregularities which obscure the background levels.

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A comparison of EISCAT and SuperDARN F‐region measurements with consideration of the refractive index in the scattering volume

Cited by 24 publications

References 31 publications

Improvement of HF coherent radar line-of-sight velocities by estimating the refractive index in the scattering volume using radar frequency shifting

Improvement of HF coherent radar line-of-sight velocities by estimating the refractive index in the scattering volume using radar frequency shifting

Temporal and spatial resolved SuperDARN line of sight velocity measurements corrected for plasma index of refraction using Bayesian inference

Ionospheric electron number densities from CUTLASS dual‐frequency velocity measurements using artificial backscatter over EISCAT

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