Winckler Symposium: Fast Temporal Variations in Auroral Particle Precipitation

The standard model of auroral acceleration considers the quasi-static acceleration of auroral particles in electric fields parallel to the geomagnetic field. In spite of the great successes of this model, it has been clear for many years that not all auroral phenomena could be incorporated in this model. Pulsating and flickering auroras show variations on times scales of a few seconds or less. Rocket data have shown superthermal electron bursts with similar time scales. Most recently, FAST observations have indicated that auroral particles near the polar cap boundary exhibit distributions that are broad in energy and narrow in pitch angle, in contrast to the inverted-V signature of a nearly monoenergetic peak in the electron distribution that would be predicted by the quasi-static model.

The purpose of this workshop is to bring together experimental and theoretical scientists interested in such time-dependent auroral particle acceleration. The meeting will review existing observations and identify what results are predicted by theory. Theories involving pitch-angle scattering in the outer magnetosphere as well as Alfvenic and lower hybrid wave-particle interaction mechanisms have been proposed. One of the objectives of this meeting is to see how well these theories can be validated by experimental observations. We hope there will be extensive dialogue between theorists and experimenters that will answer the questions: Do we need new theories? Do we need other measurements that are not currently available that will clarify the pulsation mechanisms?

This meeting is dedicated to the late Professor John Winckler, who had a life-long interest in pulsating aurora. Pulsating aurora is a recovery phase substorm phenomenon that usually occurs on the morning side. The electron precipitation responsible for pulsations has been studied since the fifties from ground-based observations, balloon-borne detectors, rockets and satellites. Those electrons are now thought to come from a quasi-trapped population injected near the midnight sector. There is a considerable amount of data available on waves and particles related to pulsations. However, some experiments have obtained conflicting results. For example, while previous rocket observations indicate the pulsation region is on the equatorial plane, a recent rocket experiment obtained data that indicate the region is much closer to the ionosphere. In spite of these differing results, pulsation observations and theories are fairly mature and pulsating aurora may be one of the few space plasma physics problems that can be really understood quantitatively.

This meeting is being organized under the auspices of the William I. Fine Theoretical Physics Institute in the School of Physics and Astronomy of the University of Minnesota. The keynote speech of the workshop will be held concurrently with a Physics Colloquium on Wednesday, April 21, by Paul Kellogg and George Parks, who will highlight John Winckler's contributions to this field. The workshop will continue on Thursday and Friday of that week with contributions from the community as well as time for extensive discussion.

Those who wish to participate should contact Bob Lysak (bob@aurora.space.umn.edu) to be placed on the contact list.