In order to determine the incident auroral electron spectra during the night, we took data from the Poker Flat Meridian Scanning Photometer (MSP) and determined an energy flux and characteristic energy for the electrons that would reproduce the observed brightness of the red line OI(630.0 nm) and the blue N2+ first negative band at 427.8 nm.
Zenith brightness of selected auroral emissions from the Poker Flat MSP. Note that the time axis is in UT.
The resulting energy flux and mean energy of the incident electrons is shown in this figure:
Using this electron flux, we ran the AURORA model. The following panels show some of the model output parameters. Local time is plotted along the horizontal axis. The vertical axis shows altitude in km. There is aurora at local midnight (9:00 UT) and later on during the night. During the early morning hours the effects of the rising sun can be seen. The N2 ionization rate, for example, shows clearly the decending terminator as the sun rises.
The blue and red auroral emissions as a function of time and altitude are modeled as shown in the next two panels. Integrating over altitude at each time step gives column emission rates identical to those observed by the MSP.
One well known feature of aurora is easily demonstrated by this example: the red OI(630.0 nm) emission has its origin at higher altitude than the blue N2+ first negative band at 427.8 nm. Low energy electrons do not penetrate very deep and give rise to mostly red aurora (e.g. around midnight in this example), while energetic electrons penetrate deeper and the blue N2+ first negative band becomes brighter than the red oxygen line (e.g. at about 4:00 local time).
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Last updated: 24 Jan 96