Simulating Radiation Belt Dynamics using ULF Wave Radial Diffusion Models Constrained by Dynamic Outer Boundary Conditions Derived by Mapping from LEO to HEO.
Abstract
The Van Allen Probes mission has provided the most extensive measurements of relativistic electrons flux dynamics in the heart of the Earth's outer radiation belt ever collected. Utilizing this database of relativistic electron flux measurements, analytic expressions for statistical representations of the observed equatorial pitch-angle distributions as a function of geomagnetic parameters are developed. Here we further illustrate how these analytic expressions for the pitch-angle distributions can be used in radiation belts models to simulate the outer radiation belt electron dynamics in the equatorial plane using boundary conditions derived only using low-Earth orbit (LEO) data. Specifically, we use the Halloween 2003 superstorm to illustrate this method. During this storm, ultra-relativistic electrons which are normally restricted to the outer radiation belt region were rapidly transported into the slot region and inner zone. We use a ULF wave radial diffusion model to simulate the outer belt flux dynamics and examine the impact of wave-particle interactions on the loss and acceleration of the ultra-relativistic electrons. Global ground-based magnetometer measurements of ULF waves are used to characterize the radial diffusion coefficients during this extreme storm. Electron loss is applied in the simulation to reproduce the observed rapid flux drop including loss applied on higher L-shells due to magnetopause shadowing, based on the location of the last closed drift shell, and due to possible wave-particle resonances with electromagnetic ion cyclotron (EMIC) waves. Our newly developed Van Allen Probes statistical electron pitch-angle model is used in combination with in-situ SAMPEX measurements of the electron flux in LEO to specify the outer boundary condition in the equatorial plane in our radial diffusion simulation. The cross L-shell response of the radiation belts during the Halloween storm, including penetration into the slot, is simulated in the equatorial plane using only SAMPEX data from LEO at the outer boundary. The simulation results are then compared to the SAMPEX measurements of the belt response during the Halloween storm at lower L-shells.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1143O