For the identification of magnetospheric acceleration processes, it is crucial to build up an understanding of the spatial and temporal morphology of the energy spectrum of the precipitating particles during geomagnetic storms. Collaboration between Lancaster University and MPAe (Max-Planck-Institut Aeronomie) has enabled high-resolution energy maps of the particle precipitation to be produced. DASI (Digital All-sky Imager) and IRIS images give estimates of the particle precipitations of the soft electrons (<10keV) and hard electrons (> 25keV), respectively. It is known that the ratio of absorption to the square root of optical intensity is an indicator of the energy for the precipitating electrons. EISCAT is able to make an accurate electron density profile measurement at one point within the common IRIS / DASI field of view. The energy spectrum of the precipitating electrons is computed by inverting the electron density profile measured by EISCAT. An exponential energy spectrum has been fitted to extract the characteristic energy. From this information high-resolution maps of the characteristic energy have been generated for the entire common IRIS/DASI field of view:
A time series, consisting of 3 sequential panels, showing DASI, IRIS and characteristic energy images. Each panel shows DASI optical images calibrated in Rayleighs at 557.7 nm (top in panel), IRIS absorption images calibrated in dB (middle in panel), and the characteristic exponential energy in keV (bottom in panel). Each panel starts at 20:30 UT (top panel), 20:38 UT (middle panel) and 20:46 UT (bottom panel), stepping with 1 minute integration, on 13 February 1996. The field of view covered is 67.8-70.2N and 17.75-23.75E.