Investigation of the relationship between optical auroral forms and HF radar E region backscatter

Milan, S. E.; Lester, M.; Sato, Natsuo; Takizawa, Hirotsugu; Villain, Jacques

doi:10.1007/s00585-000-0608-7

Cited by 9 publications

(8 citation statements)

References 19 publications

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“…described how E-region echoes often appear delineated into L-shell-aligned "channels" in which the echo characteristics differ, but fall into distinct populations. These channels appear to be associated with changes in field-aligned current structure, ionospheric conductivity, and the driving electric field, that is a relationship with visual auroral forms is expected, as also investigated by Milan et al (2000Milan et al ( , 2002.…”

Section: Discussionmentioning

confidence: 73%

“…Previous studies have demonstrated the existence of a number of echo types in HF radar backscatter from the E-region (Villain et al, 1987(Villain et al, , 1990Hanuise et al, 1991;Milan et al, 2003) and have also investigated the relationship between E-region backscatter and visual auroral forms (Milan et al, 2000(Milan et al, , 2002. In this study we present observations of an auroral feature made from above and below, that is by a ground-and a space-based imager simultaneously, and show the remarkable association with HF radar E-region echoes.…”

Section: Introductionmentioning

confidence: 99%

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E-region echo characteristics governed by auroral arc electrodynamics

et al. 2003

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Abstract.Observations of a pair of auroral arc features by two imagers, one ground-and one space-based, allows the associated field-aligned current (FAC) and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularitygenerating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ionacoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.

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Section: Discussionmentioning

confidence: 73%

Section: Introductionmentioning

confidence: 99%

E-region echo characteristics governed by auroral arc electrodynamics

et al. 2003

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“…10a, can effectively be thought of as a single radar with a much greater range of azimuthal look-directions, in this case close to 150 • . Milan et al (2000) used this pair of radars to show that in the electrojets if one radar observed predominantly negative velocities, the other measured positive velocities, and vice versa, consistent with the dominant direction of irregularity drift being westward or eastward. Here we exploit the extended azimuthal coverage of the radar pair to investigate the Doppler shift characteristics of the HAIR echoes.…”

Section: Hair Doppler Shift Characteristicsmentioning

confidence: 95%

“…The Iceland East radar, one of the CUTLASS radars which form the eastern-most pair of the Northern Hemisphere SuperDARN chain, has been used extensively in the past for the study of E-region backscatter (Milan and Lester, 1998, 1999Milan et al, 2000Milan et al, , 2003a. As part of these studies the "myopic" mode was developed in which the range separation is decreased to 15 km, to give high spatial resolution observations of the near-range field-of-view, that portion of the field-of-view in which E-region echoes are routinely detected.…”

Section: The Stereo Cutlass Experimentsmentioning

confidence: 99%

HF radar observations of high-aspect angle backscatter from the E-region

et al. 2004

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Abstract. We present evidence for the observation of highaspect angle HF radar backscatter from the auroral electrojets, and describe the spectral characteristics of these echoes. Such backscatter is observed at very near ranges where ionospheric refraction is not sufficient to bring the sounding radio waves to orthogonality with the magnetic field; the frequency dependence of this propagation effect is investigated with the Stereo upgrade of the CUTLASS Iceland radar. We term the occurrence of such echoes the "high-aspect angle irregularity region" or HAIR. It is suggested that backscatter is observed at aspect angles as high as 30 • , with an aspect sensitivity as low as 1 dB deg −1 . These echoes are distinguished from normal electrojet backscatter by having low Doppler shifts with an azimuthal dependence that appears more consistent with the direction of the convection electric field E than with the expected electron E×B drift direction. This is discussed in terms of the linear theory dispersion relation for electrojet waves.

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“…This allows for the echo characteristics to be defined much more accurately, and hence, hopefully different generation mechanisms can be distinguished. Milan et al (2000) demonstrated that indeed auroral arcs and E-region HF radar backscatter features appeared related, though unfortunately in their study, the viewing-geometry between the radar and the all-sky camera was not optimal and did not allow for the exact interlocation to be determined. A superior viewing-geometry allowed to suggest that backscatter may appear between pairs of auroral arcs (in that case separated by 200 to 300 km), or rather to be bounded at one edge by one arc and then sometime later to be bounded at the other edge by another arc.…”

Section: Introductionmentioning

confidence: 92%

The spectral characteristics of E-region radar echoes co-located with and adjacent to visual auroral arcs

et al. 2002

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Abstract. Simultaneous all-sky camera and HF radar observations of the visual and E-region radar aurora in the westward electrojet suggest a close relationship between a pair of parallel east-west-aligned auroral arcs, separated by ∼30 km, and a region of strong radar backscatter. Poleward of this a broader region of radar backscatter is observed, though the spectral characteristics of the echoes in these two regions differ considerably. We suggest that the visual aurorae and their radar counterparts are produced in a region of upward fieldaligned current (FAC), whereas the backscatter poleward of this is associated with downward FAC. Relatively low electric fields (∼10 mV m −1 ) are observed in the vicinity of the arc system, suggesting that in this case, two-stream waves are not directly generated through the electrodynamics of the arc. Rather, the generation of irregularities is most probably associated with the gradient drift instability operating within horizontal electron density gradients produced by the filamentary nature of the arc FAC system. The observation of high Doppler shift echoes superimposed on slow background flow within the region of backscatter poleward of the visual aurora is argued to be consistent with previous suggestions that the ion-acoustic instability threshold is reduced in the presence of upwelling thermal electrons carrying downward FAC.

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Investigation of the relationship between optical auroral forms and HF radar E region backscatter

Cited by 9 publications

References 19 publications

E-region echo characteristics governed by auroral arc electrodynamics

E-region echo characteristics governed by auroral arc electrodynamics

HF radar observations of high-aspect angle backscatter from the E-region

The spectral characteristics of E-region radar echoes co-located with and adjacent to visual auroral arcs

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