Abstract
We examine drift phase structure in the electron radiation belt
observations to differentiate radial transport mechanisms. Impulsive
electrostatic or electromagnetic fields can cause radial transport and
produce drift echoes (periodic drift phase structures with
energy-dependent period). Narrow-band standing electromagnetic wave
fields can also cause radial transport, while producing
energy-independent periodic drift phase structures. Broad-band,
random-phase electromagnetic wave fields can cause radial transport, but
do not necessarily produce drift phase structure. We present results of
three case studies showing little association between drift phase
structure and ~MeV electron flux enhancements in the
outer belt. We estimate the amplitude of drift phase structures expected
for impulsive or narrow-band interactions to compete with broad-band,
random-phase waves. We show that the observed drift phase structure is
typically much smaller than would be present if either impulses or
narrow-band waves were the dominant cause of radial transport. We
conclude that radial transport is primarily consistent with the
broad-band, random-phase, small perturbations assumed in quasilinear
diffusion theory, although we cannot rule out the unlikely possibility
that radial transport plays little role in radiation belt dynamics.