Using spectral characteristics to interpret auroral imaging in the 731.9 nm O<sup>+</sup> line

Abstract

Abstract.Simultaneous observations were made of dynamic aurora during substorm activity on 26 January 2006 with three high spatial and temporal resolution instruments: the ASK (Auroral Structure and Kinetics) instrument, SIF (Spectrographic Imaging Facility) and ESR (EISCAT Svalbard Radar), all located on Svalbard (78 • N, 16.2 • E). One of the narrow field of view ASK cameras is designed to detect O + ion emission at 731.9 nm. From the spectrographic data we have been able to determine the amount of contaminating N 2 and OH emission detected in the same filter. This is of great importance to further studies using the ASK instrument, when the O + ion emission will be used to detect flows and afterglows in active aurora. The ratio of O + to N 2 emission is dependent on the energy spectra of electron precipitation, and was found to be related to changes in the morphology of the small-scale aurora. The ESR measured height profiles of electron densities, which allowed estimates to be made of the energy spectrum of the precipitation during the events studied with optical data from ASK and SIF. It was found that the higher energy precipitation corresponded to discrete and dynamic features, including curls, and low energy precipitation corresponded to auroral signatures that were dominated by rays. The evolution of these changes on time scales of seconds is of importance to theories of auroral acceleration mechanisms.

First direct optical observations of plasma flows using afterglow of in discrete aurora

“…For this mechanism, the thermal distribution of O( 3 P) between the levels with J ¼ 0; 1; 2 determined the production rate of the 2 P 1=2 and 2 P 3=2 states, assuming conservation of J. Dahlgren et al (2008b) used the spectrographic imaging facility on Svalbard to study the same emissions in active aurora, and found a ratio of 1.6.…”

“…(3). The question of isolating the emission spectrally from contaminating N 2 1PG and OH airglow is treated elsewhere (Dahlgren et al, 2008b). The ASK filter has central wavelength of 732.0 nm and a FWHM of 1.0 nm to isolate the stronger line of the doublet, and minimize the contribution from contaminating emissions.…”

“…All images and keograms have been dark and flatfield corrected and a background level has been subtracted. The ASK2 filter has a FWHM of 1.0 nm; the data are contaminated in this wavelength interval by the N 2 1PG band as well as by OH airglow (see Dahlgren et al, 2008b for a full analysis). In the first event, on 9 November 2006, ASK1 is imaging a wavelength interval of the N 2 1PG emission band.…”

Compound auroral micromorphology: ground-based high-speed imaging

“…Dahlgren et al (2008a) reported that some auroral filaments are caused by higher energy precipitation within regions of lower energy precipitation, whereas other filaments are the results of a higher flux compared to the surroundings. It was also found that high-energy precipitation corresponds to discrete and dynamic features, including curls, and low-energy precipitation corresponds to auroral signatures that were dominated by rays (Dahlgren et al 2008b). Further, Dahlgren et al (2012) identified that mono-energetic approximately 8 keV electron precipitation caused extremely narrow (approximately 70 m) and highly dynamic auroral filaments.…”

Coexisting structures from high‐ and low‐energy precipitation in fine‐scale aurora

“…The second imager captures the forbidden O + emission at 732.0 nm (I O + ), which has a lifetime of ∼5 s. This emission is produced in the F region due to low-energy precipitation. At this wavelength there are also underlying N 2 emission bands, produced by high-energy precipitation [Dahlgren et al, 2008a]. The third imager measures the atomic oxygen emission at 777.4 nm (I O ), which in the aurora is most sensitive to low-energy precipitation [Lanchester et al, 2009] and results from direct excitation of atomic oxygen in the ionospheric F region.…”