Multispectral observations of auroral rays and curls

Abstract

Two cases of discrete aurora are presented, in which auroral curls and auroral rays, respectively, were seen. The aurora was imaged by two spatially separated imagers with a long‐pass filter (mainly sensitive to N2 and N2+ emissions), and another imager with a narrow‐band 7325 Å filter (sensitive to forbidden O+ doublet). Also, spectra of the aurora were recorded. Using the multispectral imaging and spectra we find that the curls occurred in aurora caused by precipitation of energetic electrons with a lack of low‐energy population, while in the rays both high and low energy precipitation were present simultaneously. These findings are confirmed by the altitude determination from triangulation.

Morphology and dynamics of aurora at fine scale: first results from the ASK instrument

“…6), the aurora is characterised by slowly evolving rays. Consequently, rayed structure is here associated with the presence of low energy emission, which is in agreement with the results of Ivchenko et al (2005). It is important to note, however, that the aurora is not evenly filling the HiTIES panels during the rayed periods.…”

“…This O + enhancement was also shown to be linked with the presence of rayed arcs. Ivchenko et al (2005) presented a study in which an auroral curl was shown to lack low energy precipitation, while rayed structures contained both high and low energy precipitating flux. These studies strongly suggest that there can be physical differences in the generation mechanisms resulting in auroral curls and rays.…”

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

“…Such features are not typical for arc-like extended filaments present during high energy aurora. This is in agreement with Ivchenko et al (2005).…”

“…Pallamraju and Chakrabarti (2005) have used an imaging spectrograph named HIRISE to study daytime aurora at high spectral resolution, and Ivchenko et al (2005) used the Spectrographic Imaging Facility (SIF) on Svalbard combined with incoherent scatter radar and optical measurements to investigate the O + 4 P − 4 D o multiplet in an electron aurora event. A spectrographic analysis of curls and rays (Ivchenko et al, 2004) showed that different emissions are present in different auroral configurations.…”

Sounding rocket study of two sequential auroral poleward boundary intensifications

“…The visible signatures are very active and dynamic, with swirling rays moving along the curtain at 8 km/s or faster, some in the geomagnetic east direction and some in the geomagnetic west direction, in a limited latitudinal band of one degree. Ivchenko et al [2005] report observations relating thin rayed aurora to Alfvénic acceleration.…”