Boundary-Oriented Electron Precipitation Model

A boundary-oriented model of the global configuration of electrons precipitating into the polar ionosphere is presented. It provides the differential energy flux of precipitating electrons from 32 eV to 30 keV for five different activity levels. Data from twelve years and eight DMSP spacecraft were incorporated into the model. The defining characteristic of this model is that only observations similarly located relative to auroral boundaries (e.g. observations just equatorward of the open–closed boundary) are averaged together. The model resulting from this approach more closely resembles instantaneous observations than previous efforts. There is a distinct polar cap surrounded by a narrow auroral zone, transitions between different regions are appropriately sharp, and model spectra are more realistic. This increased fidelity with observation is a significant advantage for the model, broadening its applicability. Also new, is the calculation of both mean and median model spectra. The mean is dominated by sporadic flux enhancements, where present, while the median resembles more commonly observed background fluxes, permitting both of these aspects to be addressed. Parameterization for activity is based on the degree of magnetotail stretching, as indicated by the latitude of the ion isotropy boundary. A variety of features can be discerned in the model. There is a large difference between the mean and median energy flux in regions where upward region 1 Birkeland currents are commonly observed. The smooth ~1-10 keV precipitation seen at most local times, in the equatorward portion of the oval, is nearly absent in much of the afternoon sector. Enhanced number fluxes are seen at the poleward edge of the oval near midnight, likely due to the frequent presence of fieldaligned bursts. Structured precipitation dominates the energy flux at all local times except between dawn and noon, where the contribution from unstructured precipitation dominates. The total hemispheric energy flux due to mean spectra varies with activity from 6 to 38 GWatts, and exceeds the energy flux due to median spectra by a factor of approximately 4, regardless of activity.