Investigation of the characteristic energy of the auroral electrons based on ALIS observations
The characteristic energy of particles precipitating into the upper atmosphere is an important parameter for a better understanding of the ionosphere-magnetosphere coupling. This report presents an investigation of the characteristic energy of the auroral electrons based on ALIS observations.
The Auroral Large Imaging System is a ground-based network of six remote-controlled stations situated in Northern Scandinavia providing monochromatic images of high-altitude optical phenomena in several wavelengths (5577 Ă…, 6300 Ă…, 4278 Ă… and 8446 Ă…).
Two different approaches have been used to retrieve the characteristic energy of the auroral electrons.
The first technique is based on ratios between measured auroral line intensities. Since excited states of atoms and molecules, from which the auroral optical emissions originate, are formed by both direct electron impact and chemical reactions, intensities of auroral emissions at different wavelengths are indeed important indicators of both the auroral particle flux and the thermosphere-ionosphere composition. The second technique takes advantage of the multi-imaging aspect of the ALIS network and consists in determining the height of the aurora by triangulation. The height of the aurora is in fact closely related to the characteristic energy of the precipitating particles since the more energetic auroral electrons penetrate deeper into the atmosphere.
By means of theoretical modelling of both the emission processes and the electron transport through the atmosphere based on two different primary electron spectra, it has been possible to relate those experimental intensity ratio and height data to the characteristic energy of auroral electrons. The excellent fitting of the results deduced from those two different approaches validates both the ALIS absolute calibration and the theoretical models. It is a first promising step for further investigation.
Created 2009-07-01 13:21:08 by Mats HolmstrĂ¶m Last changed 2009-07-01 13:21:08 by Mats HolmstrĂ¶m