Pitch Angle Distribution Analysis from the CRRES MEA - Average Picture and Radial Diffusion versus Local Heating

Details Pitch Angle Distribution Analysis from the CRRES MEA - Average Picture and Radial Diffusion versus Local Heating Pitch Angle Distribution Analysis from the CRRES MEA - Average Picture and Radial Diffusion versus Local Heating

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm33a0443g&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM33A-0443

Physics

2700 Magnetospheric Physics (6939), 2720 Energetic Particles: Trapped, 2730 Magnetosphere: Inner

Scientific paper

Variations in electron phasespace density at a particular location can be indicative of a specific energization or loss process. Determining the nature of that process as diffusive or local heating can be difficult to do. However, these processes can also leave different signatures on the pitch angle distributions (PADs) of a particle population, such that changes at a single location can give us important clues to the factors producing electron flux variations. Using data from the medium electron A instrument (MEA) on the CRRES satellite, a survey of PADs of energetic electrons is performed. The distributions are classified into three types (butterfly, 90-degree peaked, and flattop) based on the ratio of counts at 90 degrees and the average of the counts at 45 and 135 degrees. The categorizations are examined as a function of L-shell, localtime, orbit number and geomagnetic activity. The 90-degree peaked distributions tend to dominate on the dayside and in the lowest energy channel (153keV). Butterfly distributions are more prevalent at higher L-shells and on the nightside. During periods of moderate geomagnetic activity, we see an increase in butterfly distributions at L-shells greater than on the nightside and for 3.5 < L < 5.5 on the dayside. We also find significant differences in the average PAD before and after the great storm of March 24, 1991. Knowing the typical PAD types in a region, and the dependencies on other parameters, we can look for changes that might indicate a particular energization process is occurring. Radial diffusion tends to favor local 90-degree particles. As diffusion occurs, the pitch angle distribution becomes more 90-degree peaked, or transitions from one type of distribution to another, for example butterfly to flattop. We show examples of the diffusion of PADs at higher L-shells, consistent with radial diffusion, and examples inconsistent with radial diffusion at lower L-shells and near the plasmapause.

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