Modeling of the Atmosphere Magnetosphere Ionosphere System (MAMI)

Example of the AMIE model

In order to show an example of an analysis using DE-1 images and AMIE in concert, we have selected a period of almost 2 hours where we have continuous image data. This period is in the middle of a 16 hour period for which Kamide et. al (J. Geophys. Res., 99, 10,451, 1994) have identified six substorms. This period was part of a magnetosphere-ionosphere-thermosphere radar studies campaign (MITHRAS) for which an extensive data set was collected. Kamide et. al studied the ionospheric convection associated with auroral substorm expansion using the AMIE technique. The following figure shows a graph of high latitude geomagnetic activity form 67 observatories for this period, October 25, 1981 (see Kamide et al. ). The arrows indicate substorm onsets. The period for which we also have DE-1 images available is highlighted.

For our analysis we need simultaneous images in different wavelength regimes. For this period we have UV images consisting of auroral emissions from atomic oxygen and N₂, and images with a narrow passband filter to single out the N₂⁺ first negative emissions at 391.4 nm wavelength. The latter also has large non-auroral source, namely from scattered sunlight, even far into the nightside. These images thus require that the auroral emissions are isolated before we apply our analysis to obtain conductances.

Using this analysis technique, we obtain ionospheric conductances covering the entire region where the aurora appears for the period covered by the satellite image data. The solar UV radiation produces additional ionization and conductance in the sunlit part of the atmosphere. Together with magnetic field measurements from the ground, AMIE derives the currents and convection in the ionosphere. The output from AMIE and the temporal and spatial development of ionospheric parameters can be illustrated in animated plots. Here we show (as mpeg animations, 183kB) the average energy flux into the aurora and the Hall conductance, overlaid with ionospheric current vectors.

The period of useful image data in this case is shorter than a typical substorm, posing a limitation on this analysis. The new imagers on the POLAR spacecraft (launched 24 Feb 1996) will not only provide higher temporal and spatial resolution that the data presented here, but the orbit of the spacecraft will allow continuous coverage of most of the nightside aurora for approximately 10-12 hours.

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Last updated: 3 September 96
Questions? Comments? Please send E-mail to lumm@gi.alaska.edu