Pulsating aurora

Thomas, Richard William (1982) Pulsating aurora. University of Southampton, Doctoral Thesis.

Abstract

Extensive observations of the Aurora Borealis (an optical display in the upper atmosphere at high latitudes in the northern hemisphere) were made from Andøya, Skibotn and Spitzbergen in Northern Norway over a period of four years (1977/78/ 79/80), using low-light television cameras (All-Sky and narrow angle). Together with previously recorded All-Sky video data from Alaska (taken in 1976), a comprehensive study was made of pulsating aurora. This describes a type of aurora which undergoes on-off modulations in intensity with a periodicity of 2-20 seconds, and is observed in a variety of forms. A number of additional features have arisen from the study, these being: 1. A latitude effect in the periodicity of auroral pulsating patches, suggesting strongly that one of the modulating mechanisms involved depends on the length of the geomagnetic field-line. 2. Using time-lapse integrated TV recordings (which accentuate long period spatial motions) a distinctive type of behaviour was observed in the auroral luminosity near the poleward edge of the diffuse aurora. This has been termed 'Recurrent Propagating Aurora' and is seen to be a spatial propagation of luminosity rather than a temporal variation so characteristic of pulsating patches in the late recovery phase of an auroral solar storm in the morning sector. Finally, simultaneous conjugate observations between the GEOS II geostationary satellite and an All-Sky TV camera operated at the footprint position are presented. The occurrence of pulsed hiss at GEOS and auroral pulsating patches near the footprint position were found to have a close statistical similarity. Individual pulsating events are analysed in detail, and the relationship between the observed modulated wave noise and electron precipitation pulsations is discussed. The strength of wave noise at geostationary orbit was found to be too weak to explain the electron pitch-angle distributions above pulsating auroras recorded by previous researchers.

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