Auroral optical observations of plasma processes

Plasma processes which occur in the near-earth environment are normally observed by techniques which provide one dimensional information for a given point in time. Spatial information is obtained at the expense of simultaneity of measurements by sweeping through what is clearly a highly dynamic region as is apparent by any casual inspection of the optical output of magnetospheric processes. On the other hand, appropriate imaging technology either from ground or satellite can reveal the instantaneous two-dimensional character of such plasma dynamics. Particularly conducive to such measurements are the vortical structures which develop with varying horizontal dimensions in the ionosphere near 120 m attitude. 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 vorticles (sometimes up to 7) which can extend over several thousand km. 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