Empirically estimated electron lifetimes in the Earth’s radiation belts:
2. Comparison with theory
Abstract
We compute quasilinear diffusion rates due to pitch-angle scattering by
various mechanisms in the Earth’s electron radiation belts. The
calculated theoretical lifetimes are compared with observed decay rates
and we find excellent qualitative agreement between the two. The overall
structure of the observed lifetime profiles as a function of energy and
is largely due to plasmaspheric hiss and Coulomb scattering. The results
also reveal a local minimum in lifetimes in the inner zone at lower
energy (~50 keV), attributed to enhanced scattering via
ground-based VLF transmitters, and a reduction in lifetimes at higher
and energy (>1 MeV), attributed to enhanced EMIC wave
scattering. In addition, we find significant quantitative disagreement
at <3.5, where the theoretical lifetimes are typically a
factor of ~10 larger than the observed, pointing to an
additional loss process that is missing from current models. We discuss
potential factors that could contribute to this disagreement.