Effects of localized sources on quiet time plasmasphere electron precipitation

Abstract

During geomagnetically quiet times, particle precipitation at low to middle latitudes (Lapproximately-less-than4) results from a combination of pitch angle diffusion into the bounce loss cone and the opening of the bounce loss cone in the direction of drift to a maximum value which defines the drift loss cone. Some previous observations suggest that the pitch angle scattering of kilovolt electrons in the plasmasphere occurs in a localized region of space rather than throughout the course of their azimuthal drift. If their source is localized, quasi-trapped particles outside of the source region precipitate into the atmosphere at a rate that can be correlated with the rate of increase of the bounce loss cone angle in the direction of drift. Source localization also affects pitch angle distributions which are characterized by the maximum loss cone encountered during the course of the particles' azimuthal drift. Patterns describing the precipitation of quasi-trapped particles and the spatial evolution of the pitch angle distribution at a specific L value can be constructed for hypothetical localized sources. A simple idealized model, in which the source is represented by a delta function in space, leads to a qualitative picture of the morphology of precipitation in both northern andmore » southern hemispheres in the two cases of a fixed magnetospheric (i.e., local time) and fixed geographic (i.e., longitude) source. The nature of mid-latitude sources can be inferred from a comparison of observations of quasi-trapped and precipitating particles with the characteristics predicted by these models. Some observations of pitch angle distributions of 29-keV and 59-keV electrons at Lapprox. =2 from the satellite 1972-76B exhibit some of the features that characterize a highly localized source. These data can be interpreted as evidence of a corotating source fixed in the longitude interval 45degree-180degreeE.« less