The THEMIS all-sky imaging array—system design and initial results from the prototype imager

Donovan, E.; Mende, S. B.; Jackel, B. J.; Frey, H. U.; Syrjäsuo, M.; Voronkov, I.; Trondsen, T.; Peticolas, L. M.; Angelopoulos, V.; Harris, S.; Greffen, M.; Connors, Martin

doi:10.1016/j.jastp.2005.03.027

Cited by 166 publications

(169 citation statements)

References 48 publications

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“…see Henderson, 2004;Henderson et al, 2006a,b). On the other hand, the two events reported by Voronkov et al (2003) and Donovan et al (2006) occurred under much quieter nonstorm conditions (K p was 3 − and 3 • , respectively). It would therefore appear that these types of onsets can occur under a variety of conditions and are not isolated to storm-time conditions.…”

Section: Discussionmentioning

confidence: 87%

“…We note that the event examined here is very similar to a handful of events that have been studied in the past. Early examples obtained with the Viking UV imager have been presented (Henderson, 1994;Elphinstone et al, 1995) and more recently, a few cases from ground-based imagers have been reported (Voronkov et al, 2003;Donovan et al, 2006). Two of the clearest substorm onsets showing arc-aligned azimuthally periodic bright spots from the Viking imagery occurred on 24 November 1986 at 10:12:11 UT and on 23 September 1986 at 20:51:46 UT.…”

Section: Discussionmentioning

confidence: 98%

“…This class of model has come to be know as an "outside-in" model because the mid-tail activates first which later induces activity nearer to the Earth. Testing these two classes of models is a major objective of the recently launched THEMIS mission (Donovan et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Observational evidence for an inside-out substorm onset scenario

Henderson

2009

Ann. Geophys.

100

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Abstract. We present observations which provide strong support for a substorm expansion phase onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The evolution of the auroral intensity is consistent with an exponential growth with an e-folding time of around 188 s (corresponding to a linear growth rate, γ of 5.33×10 −3 s −1 ). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onset. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called "inside-out" substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

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Section: Discussionmentioning

confidence: 87%

Section: Discussionmentioning

confidence: 98%

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Observational evidence for an inside-out substorm onset scenario

Henderson

2009

Ann. Geophys.

100

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“…The DAISY exposure times are chosen to be just long enough to obtain a reasonable signal-to-noise ratio, but on the other hand short enough to result in as little motion blurring as possible. We used an exposure time of four seconds and an image cadence of 12 s. The 12-s cadence was selected to be a multiple of the imaging interval used in the Time History of Events and Macroscale Interactions During Substorms (THEMIS) (Donovan et al, 2006) cameras. Simultaneous all-sky images from the surrounding stations help in bringing the finer-scale structures into a larger context.…”

Section: Colour Datamentioning

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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“…The first large-scale deployment of low-cost auroral imaging systems was as part of the THEMIS (Time History of Events and Macroscale Interactions during Substorms) ground-based observatory (Donovan et al, 2006;Harris et al, 2008). This project operates white-light all-sky imagers at 20 remote field sites in northern Canada and Alaska.…”

Section: Low-cost Auroral Imagingmentioning

confidence: 99%

Auroral spectral estimation with wide-band color mosaic CCDs

Jackel

Unick

Syrjäsuo

et al. 2014

Geosci. Instrum. Method. Data Syst.

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Abstract. Optical aurora can be structured over a wide range of spatial and temporal scales with spectral features that depend on the energy of precipitating particles. Scientific studies typically combine data from multiple instruments that are individually optimized for spatial, spectral, or temporal resolution. One recent addition combines all-sky optics with color mosaic CCD (charge-coupled device) detectors that use a matrix of different wide-band micro-filters to produce an image with several (often three) color channels. These devices provide sequences of two dimensional multispectral luminosity with simultaneous exposure of all color channels allowing interchannel comparison even during periods with rapidly varying aurora. At present color auroral image data are primarily used for qualitative analysis. In this study a quantitative approach based on Backus-Gilbert linear inversion was used to better understand the effective spectral resolution of existing and proposed instruments.Two spectrally calibrated commercial detectors (Sony ICX285AQ and ICX429AKL) with very different color mosaics (RGB (red, green, blue) vs. CYGM (cyan, yellow, green, magenta)) were found to have very similar spectral resolution: three channels with FWHM (full-width halfmaximum) ≈ 100 nm; a NIR (near infrared) blocking filter is important for stabilizing inversion of both three-channel configurations. Operating the ICX429AKL in a noninterlaced mode would improve spectral resolution and provide an additional near infrared channel. Transformations from arbitrary device channels to RGB are easily obtained through inversion. Simultaneous imaging of multiple auroral emissions may be achieved using a single-color camera with a triplepass filter. Combinations of multiple cameras with simple filters should provide ∼ 50 nm resolution across most of the visible spectrum. Performance of other instrument designs could be explored and compared using the same quantitative framework.

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The THEMIS all-sky imaging array—system design and initial results from the prototype imager

Cited by 166 publications

References 48 publications

Observational evidence for an inside-out substorm onset scenario

Observational evidence for an inside-out substorm onset scenario

Observations of the auroral width spectrum at kilometre-scale size

Auroral spectral estimation with wide-band color mosaic CCDs

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