Characterizing the Earth's outer Van Allen zone using a radiation belt content index

Abstract

We have utilized knowledge acquired from near‐Earth spacecraft missions to construct a “radiation belt content” (RBC) index. This index sums radiation belt electron fluxes above several chosen threshold energies (most commonly, E > 2 MeV) and over the range of magnetic L shells 2.5 ≤ L ≤ 6.5. The method takes account of pitch angle distribution effects and magnetic flux tube properties. As constructed, the RBC index gives a simple, robust, and readily utilized daily estimate of the total number of electrons throughout the entire outer Van Allen radiation belt. We show correlative comparisons with concurrent solar wind parameters, geomagnetic indices, and geostationary orbit (GOES) data sets. We also examine statistical and recurrence characteristics of the RBC index itself. Results are compared with some of the orbit‐integrated dose results from the Highly Elliptical Orbit (HEO) satellite 1997‐068 that covers the same L range. The correlation of the RBC index with various spacecraft data clearly illustrates the remarkable coherence of the outer Van Allen radiation belt previously described, for example, by Kanekal et al. [2001]. Although the RBC index may be viewed as suppressing much of the spatial information content of the direct electron measurements in the outer trapping zone, it nonetheless gives a useful tool for statistical and time series analysis. The utilization of such a long‐term, homogeneous index for space weather purposes is suggested.