The Motion and Structure of Auroral Patches: A Neuroscientist's View

The term 'patchy aurora' refers to irregularly shaped 'blobs' that form a characteristic patch pattern in auroral image data. Patches are most often observed at mid to low auroral latitudes, equatorward of the peak in the proton aurora. One of the remarkable features of patchy aurora is the coherent and almost constant shape of the patches, which can be present for minutes at a time in the field of view of a single all sky camera. The structure of an individual patch is often maintained as it drifts in longitude through a camera field of view. This behavior is thought to be a consequence of plasma dynamics (and structure) in the region Earthward of the central plasma sheet. Here we present a comprehensive survey of the motion and shape of auroral patches as a function of latitude and MLT. Statistics are derived from a cross-disciplinary collaboration between the fields of neuroscience and space physics. Specifically, we employ a modified stereological approach to quantify length and orientation of patchy aurora. Stereological quantification has been successfully employed in biological systems, typically to estimate the size, shape, or number of objects within a specific region of interest. One of the central tenets of stereology is the random, systematic sampling method, which has been demonstrated to produce accurate results. We adopt a modified stereological procedure, using random, systematic sampling to produce an unbiased estimate of patch length and orientation within the aurora. The output of this procedure is also used to follow individual patches and produce velocity fields in a given image. These techniques allow us to quantify the evolution of both individual patches and the patchy aurora region as a whole. We also discuss the future possibility of using this technique to produce a semi-automated convection map for specific events. We assert that these maps will provide a time-evolving picture of the 2D convection velocity in the ionosphere with excellent space and time resolution.