Wave dispersion and the discrete aurora: New constraints derived from high‐speed imagery

Semeter, J. L.; Zettergren, M. D.; Díaz, M.; Mende, S. B.

doi:10.1029/2008ja013122

Cited by 58 publications

(68 citation statements)

References 35 publications

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“…As pointed out by Semeter et al (2008), already a few degrees off the magnetic zenith can cause a significant error in the width measured from the image. This is especially true for fine-scale aurora.…”

Section: Discussionmentioning

confidence: 99%

Observations of the auroral width spectrum at kilometre-scale size

et al. 2010

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Abstract. This study examines auroral colour camera data from the Canadian Dense Array Imaging SYstem (DAISY). The Dense Array consists of three imagers with different narrow (compared to all-sky view) field-of-view optics. The main scientific motivation arises from an earlier study by Knudsen et al. (2001) who used All-Sky Imager (ASI) combined with even earlier TV camera observations (Maggs and Davis, 1968) to suggest that there is a gap in the distribution of auroral arc widths at around 1 km. With DAISY observations we are able to show that the gap is an instrument artifact and due to limited spatial resolution and coverage of commonly used instrumentation, namely ASIs and TV cameras. If the auroral scale size spectrum is indeed continuous, the mechanisms forming these structures should be able to produce all of the different scale sizes. So far, such a single process has not been proposed in the literature and very few models are designed to interact with each other even though the range of their favourable conditions do overlap. All scale-sizes should be considered in the future studies of auroral forms and electron acceleration regions, both in observational and theoretical approaches.

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Section: Discussionmentioning

confidence: 99%

Observations of the auroral width spectrum at kilometre-scale size

et al. 2010

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“…The range of arc widths (5-35 km) is representitive of a continuous distribution with a lower limit cutoff at 5 km due to the instrument resolution (Partamies et al, 2010). While Knudsen et al (2001) found arc widths larger than 35 km, this result is likely biased towards larger widths due to the aspect angle problem (Semeter et al, 2008;Partamies et al, 2010). Also, Knudsen et al (2001) defined arc widths at 135 km altitude, and so these widths will be slightly larger than those here which are defined at 100 km.…”

Section: Synthetic Imagesmentioning

confidence: 77%

A new automatic method for estimating the peak auroral emission height from all-sky camera images

Whiter

Gustavsson

Partamies

et al. 2013

Geosci. Instrum. Method. Data Syst.

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Abstract. This paper presents a new fully automatic method for quickly finding the average peak emission height of a single auroral structure from a pair of all-sky camera images with overlapping fields of view. The peak emission height of the aurora must be estimated in order to calculate several other important parameters, such as horizontal spatial scales, optical flow velocities, and ionospheric electric fields. In most cases the height is not measured, but a value is assumed, often about 110 km. It is unclear how accurate this assumption is. A future statistical study of the auroral height in which the method presented here will be applied to many years of observations will lead to more accurate assumptions of the height with quantitative error estimates, and therefore more accurate estimates of parameters derived using these assumed auroral heights. In the present work the performance of the new method is compared to another recent automatic method. It is found that the new method measures the peak emission height regardless of the shape of the volume emission rate profile, unlike the other recent method. However, the new method is less suitable than the other method for analysis of very wide auroral arcs (> 30 km) or for aurora in the magnetic zenith of one of the images.

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“…The BG3 filter is used to examine only the prompt emissions; it is a notch filter that cuts out the region of the spectrum that contains the slow 557.7 and 630.0 nm emissions and lets in the prompt blue and near-infrared emissions. A transmission curve for the BG3 filter is reproduced in Semeter et al (2008). The high time resolution of the image data reveals flaming aurora, with apparent motion of structures toward the magnetic zenith.…”

Section: Event 1: Substorm Onset With Flaming Aurora -1 March 2011mentioning

confidence: 98%

Characteristics of Poker Flat Incoherent Scatter Radar (PFISR) naturally enhanced ion-acoustic lines (NEIALs) in relation to auroral forms

2014

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Abstract. Naturally enhanced ion-acoustic lines (NEIALs) have been observed with the Poker Flat Incoherent Scatter Radar (PFISR) ever since it began operating in 2006. The nearly continuous operation of PFISR since then has led to a large number of NEIAL observations from there, where common-volume, high-resolution auroral imaging data are available. We aim to systematically distinguish the different types of auroral forms that are associated with different NEIAL features, including spectral shape and altitude extent. We believe that NEIALs occur with a continuum of morphological characteristics, although we find that most NEIALs observed with PFISR fall into two general categories. The first group occurs at fairly low altitudes -F region or below -and have power at, and spread between, the ion-acoustic peaks. The second group contains the type of NEIALs that have previously been observed with the EIS-CAT radars, those that extend to high altitudes (600 km or more) and often have large asymmetries in the power enhancements between the two ion-acoustic shoulders. We find that there is a correlation between the auroral structures and the type of NEIALs observed, and that the auroral structures present during NEIAL events are consistent with the likely NEIAL generation mechanisms inferred in each case. The first type of NEIAL -low altitude -is the most commonly observed with PFISR and is most often associated with active, structured auroral arcs, such as substorm growth phase, and onset arcs and are likely generated by Langmuir turbulence. The second type of NEIAL -high altitude -occurs less frequently in the PFISR radar and is associated with aurora that contains large fluxes of low-energy electrons, as can happen in poleward boundary intensifications as well as at substorm onset and is likely the result of current-driven instabilities and in some cases Langmuir turbulence as well. In addition, a preliminary auroral photometry analysis revealed that there is an anticorrelation between the altitude of the NEIALs and the calculated energy of the electrons, which is consistent with the hypotheses presented here regarding generation mechanisms.

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Wave dispersion and the discrete aurora: New constraints derived from high‐speed imagery

Cited by 58 publications

References 35 publications

Observations of the auroral width spectrum at kilometre-scale size

Observations of the auroral width spectrum at kilometre-scale size

A new automatic method for estimating the peak auroral emission height from all-sky camera images

Characteristics of Poker Flat Incoherent Scatter Radar (PFISR) naturally enhanced ion-acoustic lines (NEIALs) in relation to auroral forms

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