E. M. Blixt

Multispectral observations of auroral rays and curls

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 ( main ...

Optical flow analysis of the aurora borealis

Optical observations of the aurora have traditionally focused on the structure, intensity, and wavelength of the emissions. But the apparent motion of auroral forms offers another important diagnostic tool for investigating this poorly understood phenomenon. Prior analyses of auroral motion have focused on tracing individual features. In this letter, we investigate the feasibility of deriving the entire two-dimensional velocity field automatically using robust optical flow estimation. The analysis is applied to two narrow-field video sequences. Both examples are rich in small-scale structure and motion, but appear very different to the eye. The robust optical flow estimator performed well for regions of dense turbulent motion, while sheared flow and flow which is perpendicular to image intensity gradients, was poorly resolved. The relative magnitude of the outliers provides a quantitative measure of the validity of the underlying flow model and, hence, a means of automatically differentiating among auroral forms with differing physical origins. The technique can be used to deduce ionospheric electric fields and neutral winds, and the flow fields yield important physical information about the generation mechanism.

Conditional integration of Incoherent Scattering in relation to flickering aurora

[1] In this report we present incoherent scatter radar (ISR) observations of ionospheric response to precipitation causing flickering aurora. Flickering aurora is caused by electron precipitation with modulations at frequencies higher than 5 Hz. To resolve the variation at these short time-scales with ISR we have integrated together pulses at the same phase of the optical intensity variation observed with high-speed narrow field-of-view imaging in white light to determine the intensity variation in the field aligned direction, which is also the direction of the beam of the EISCAT Svalbard Radar (ESR). Further we show that the 3% modulation in ISR back-scattered power can be explained with electron heating by temporally modulated electron precipitation and electron cooling in collisions with ions and neutrals.