Estimate of auroral electron spectra, the power of ground-based multi-station optical measurements

Ground-based multi-station optical imaging has a great inherent scientific potential for investigations of the magnetosphere-ionosphere-thermosphere i nteractions by using inversions of the ionospheric optical signal, the auro ra. Two methods for estimating characteristics of primary auroral electron spec tra are compared and used to describe an auroral event. One method uses the spectral information in the images and the other method is based on the in version of the N(2)(+)1NG 4287 Angstrom altitude distribution. With the sec ond method ALIS can currently give estimates of the primary electron distri bution with medium time resolution (10 s). The auroral event, a passage of an eastward moving fold in a pre-existing a uroral are, is analysed and characteristics of the precipitating electrons show regions with different fluxes, e.g. a soft region that has previously been found inside the fold appears to belong to a wider region of soft prec ipitation that emerges as the are activates. (C) 2001 Elsevier Science Ltd. All rights reserved.