Abstract
Drift Orbit Bifurcation (DOB) has been suggested to play a major role in
the loss and transport of radiation belt electrons since it violates the
second and third adiabatic invariants of particles. Results from our
guiding-center test particle simulations using the Tsyganenko-1989c
magnetic field model show that the DOB could affect a broad region of
the outer radiation belt, which can penetrate inside the geosynchronous
orbit at Kp ≥ 3, and its effects are more significant further away from
Earth, at higher Kp, and for higher electron energies. Specifically, the
short-term simulation results after one electron drift show both
traditional and nontraditional DOB transport of electrons, with the
nontraditional DOB, caused by a third minimum of the magnetic field
strength near the equator, reported here for the first time. Moreover,
our results show large ballistic jumps in the second invariant and
radial distance for electrons at high equatorial pitch angles after one
drift. In addition, long-term DOB transport coefficients of electrons
over many drifts are calculated based on our simulation results. We find
that the pitch angle and radial diffusion coefficients of electrons due
to DOB could be comparable to or even larger than those caused by
electron interactions with chorus and ULF waves, respectively. In sum,
our results demonstrate that DOB could cause effective loss and
transport of radiation belt electrons even in the absence of waves.