Auroral optical observations of plasma processes

Summary form only given. Appropriate imaging technology either from ground or satellite can reveal the instantaneous two-dimensional character of plasma dynamics in the near-Earth environment. Particularly conducive to such measurements are the vortical structures which develop with varying horizontal dimensions in the ionosphere near an altitude of 120 km. UV measurements made from the Viking satellite have for the first time shown the development of such spatial features at all local times within the auroral distribution, and they always have a counterclockwise sense when viewed along the local magnetic field vector. Scale sizes vary from instrumental threshold (~20 km) to in excess of 1000 km with the larger scale sizes primarily associated with substorm activity in the midnight sector. Of special significance is the dynamic nature (lifetimes as short as 2 min) of multiple vortices (sometimes up to 7) which can extend over several thousand kilometers. These features are thought to be the result of an exponential growth along a magnetic field line of an upward field-aligned current perturbation. Such perturbations are the results of velocity/density shears along one of the many boundaries in the magnetosphere