Fine-scale optical observations of Aurora

Abstract

High spatial and temporal resolution observations of auroral forms made by the University of Calgary Portable Auroral Imager are reviewed. Observations include auroral forms with apparent widths of on the order of tens to hundreds of meters and lifetimes of less than a second to several tens of seconds. Included here is a class of multiple auroral arc systems exhibiting a strikingly asymmetric internal topology. It is shown that such systems of multiple linear arcs may be explained by mode conversion of field-line resonance shear Alfvén waves to inertial Alfvén waves. A survey of small-scale, short-lived auroral vortices (curls) occurring on thin auroral forms within the active aurora has also been performed, with some results being reviewed here. The Kelvin-Helmholtz instability as a responsible mechanism is discussed in light of the observationally acquired statistical data. Observations of small-scale “black” auroral arcs and vortices are briefly reviewed as well.