High-resolution maps of the characteristic energy of precipitating auroral particles

Abstract

For the first time we produce high-resolution maps of the characteristic energy of precipitating electrons from ground-based instrumentation in the auroral zone over northern Scandinavia. This is done by combining intensity-calibrated optical data at 557.7 nm from the Digital All-Sky Imager (DASI) with auroral absorption images from the Imaging Riometer for Ionospheric Studies (IRIS). Energy maps are produced with high temporal (10 s) and spatial (10 km) resolution within a common geographic area of 240 × 240 km. Both IRIS and DASI have the European Incoherent Scatter (EISCAT) radar within their common field of view. EISCAT is capable of making accurate measurements of the electron density height profile which, with the assistance of an atmospheric model, are inverted into equivalent energy spectra of the flux of precipitating electrons. However, incoherent scatter radars generally have a very small field of view (<1°), making studies of the energy spectrum of the precipitating particles over a wide field of view impractical. Since IRIS and DASI are sensitive to high- and medium-energy electrons, respectively, EISCAT data are used to calibrate the characteristic energy of the precipitating particles for an assumed energy spectrum against a combination of IRIS and DASI data. This empirical calibration is then used throughout the common field of view of IRIS and DASI. An initial study illustrates the spatial relationship between the different energy ranges during a substorm onset and illustrates a new way to interpret auroral phenomena. Copyright 2001 by the American Geophysical Union.