Implementing field line curvature scattering loss of ring current ions in RAM-SCB model

Ring current atmosphere interactions model with self consistent magnetic field (RAMSCB)

is a state-of-the art ring current model which self-consistently treats the

electromagnetic fields with the ring current dynamics and includes losses due to charge

exchange, coulomb collision and scattering by electromagnetic ion cyclotron (EMIC)

waves. However, for some geomagnetic storms the observed fast decay rate (time

scale < 10 hr) of ring current ions during the recovery phase, represented by the fast

recovery of the Dst index, is not well reproduced by the simulations. In this work we add

the loss due to field line curvature (FLC) scattering of ring current ions in RAM-SCB by

implementing empirical e-folding lifetimes (𝜏 ). The empirical 𝜏 was formulated from our

test particle results which simulate the scattering loss of ring current ions due to FLC.

We find that FLC scattering is efficient in fast decaying the high energy (~ 100s keV)

ions in the outer part of the ring current (L > 4) where the charge exchange and

coulomb collision rates are inefficient. After implementing the new loss due to FLC

scattering, RAM-SCB is expected to better capture the fast loss of ring current ions

during the storm recovery phase.