Empirically estimated electron lifetimes in the Earth’s radiation belts:
1. Observations
Abstract
We use measurements from NASA’s Van Allen Probes to calculate the decay
time constants for electrons over a wide range of energies (30 keV - 4
MeV) and values ( = 1.3 - 6.0) in the Earth’s radiation belts. Using an
automated routine to identify flux decay events, we construct a large
database of lifetimes for near-equatorially-mirroring electrons over a
5-year interval. We find long lifetimes (~100 days) in
the inner zone that are largely independent of energy, contrasted with
shorter, energy-dependent lifetimes (~1-20 days) in the
slot region and outer zone. We compare our lifetime calculations with
prior empirical estimates and find good quantitative agreement. The
comparisons suggest that some prior estimates may overestimate electron
lifetimes between ≈ 2.5-4.5 due to instrumental effects and/or
background contamination. Previously reported two-stage decays are
explicitly demonstrated to be a consequence of using integral fluxes.