Photometric investigation of precipitating particle dynamics.

Abstract

The theoretical basis and the experimental evidence for the interpretation of photometric data in terms of precipitating particle morphology will be reviewed. Particular emphasis will be laid on the interpretation of auroral morphology in terms of the spectroscopic signature of the precipitating particles. The meridian scanning photometric data will be discussed briefly to emphasize the auroral morphology related findings. The new type of monochromatic TV system which was specially developed for two-dimensional spectrophotometric auroral imaging will be described. The auroral morphology related findings will be discussed according to the local time sector of the observations. The early evening auroras are characterized by soft electron precipitation on the equatorward edge of the auroral oval. This precipitation is not a steady diffuse region but it is structured and the structures show coherent convective motion often in the westward direction. Harder precipitating features superimpose on this soft precipitation. These harder features (electrons 2keV or larger) are observable by all-sky cameras and they participate in the substorm auroral dynamics. Following substorm onsets and northward expansions the electron auroras harden considerably and the protons expand poleward. During early morning the diffuse soft regions occur poleward of the hard auroral features. These early morning hard auroral features often show very hard pulsating patches.