VERSIM-RBS, 19-24 September 2016, Hermanus RSA
Improvements to transport, loss, and source terms in a
1D radial diffusion model of relativistic electrons
Quintin Schiller(1,2), W. Tu(3), A. Ali(2), X. Li(2), D. Turner(4), H. Godinez(5)
(1)
NASA Goddard Space Flight Center, Heliophysics Division, Code 672, 8800 Greenbelt
Rd., Greenbelt, MD, USA
(2)
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO,
USA
(3)
West Virginia University, Morgantown, WV, USA
(4)
The Aerospace Corporation, Space Sciences Department, El Segundo, CA, USA
(5)
Los Alamos National Laboratory, Los Alamos, NM, USA
A common technique for modeling relativistic electrons in Earth’s outer radiation belt
is to use diffusion models. There are terms in these models that attempt to represent
various physical processes, such as momentum, pitch angle, and radial diffusion, as well
as mixed terms. However, quantifying the terms is challenging. Parameterizations of
these terms is a popular approach, with geomagnetic indices like AE, Kp, and Dst in
frequent use.
We use commonly used parameterizations in a one dimensional radial diffusion
model for the 2013 Jan 13-14 enhancement event, but are unable to reproduce phase
space density profiles as measured by THEMIS and the Van Allen Probes. As an
alternative, we use in-situ observations to determine radial diffusion and loss timescales.
Wave and field data from the Van Allen Probes are used to determine diffusion rates in
L*, and particle observations for the Colorado Student Space Weather Experiment
CubeSat are used to determine particle lifetimes. Additionally, a novel data assimilation
approach is used to quantify electron energization. The event specific terms are
significantly different from the parameterized terms. Furthermore, the model using
event specific terms accurately recreates THEMIS and Van Allen Probe observations.
Thus, for this event, we can accurately recreate the phase space density radial profile, as
well as the radial diffusion, loss, and source terms. We also suggest that this technique,
with only two radiation belt observatories (one equatorial and one at low altitude), is
applicable for events where the source rate is dominant.