Observations of distortions of optical features in the UV auroral distribution

• Published in: IEEE transactions on plasma science Vol. 17; no. 2; pp. 109 - 115
• Main Authors: Murphree, J.S., Cogger, L.L., Elphinstone, R.D.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.04.1989; Institute of Electrical and Electronics Engineers
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Ionosphere; Large-scale systems; Magnetic fields; Magnetosphere; Optical distortion; Optical sensors; Optical vortices; Physics of the magnetosphere; Plasma measurements; Plasma motion, convection, circulation. Plasma instabilities; Spirals; Surges; CCD imaging; Kelvin Helmholtz instability; Surge; Vorticity; Satellite observation; Magnetosphere; Auroral activity
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/27.24615

Observations made by the Viking satellite have for the first time shown the development of multiple large-scale surge features. The longer time scale of the features is contrasted with smaller-scale vortex streets found along the poleward edge of the evening oval, which are generally observed to exist for less than 2 min. The ratio of wavelength-to-diameter of these features is shown to decrease with increasing wavelength. These observations support the view that the origin of the larger surge features are of the Kelvin-Helmholtz instability type, originating further out in the magnetosphere than their vortex-street counterparts. Observations of spiral features have been made at all local times and the spirals always have a counterclockwise sense (viewed in the direction of the magnetic field in the northern hemisphere). One interpretation of these events is that they are the result of an exponential growth along a field line of an initial upward field-aligned current perturbation.< >