LARGE FLUXES OF AURORAL ELECTRONS IN FILAMENTS OF 100 M WIDTH

The combination of high time and space resolution measurements in the magnetic zenith (optical and radar) and detailed modeling of the ionos pheric response to auroral particle precipitation has produced the new result that most of the energy density in a bright are resides in an extremely narrow filament, embedded in a broader feature. We are able to show that the narrow filaments, of the order of 100 m width, are pr oduced by monoenergetic beams of electrons, whereas the surrounding em issions of lower energy density are produced by broad spectral distrib utions. The new result is achieved by combining different energy spect ra as input to an auroral model and comparing the resulting electron d ensity profiles with those measured with the European incoherent scatt er radar at 0.2 s time resolution. The result is dependent on the opti cal evidence that the narrow energetic beams do not fill the fields of view of the detectors, i.e. both photometer and radar. Agreement betw een the observed structure, scale lengths, and evolution of the aurora and modeled predictions suggests that transient parallel electric fie lds are important acceleration mechanisms above the ionosphere.