Abstract
AbstractChanges in electron flux in Earth's outer radiation belt can be modeled using a diffusion‐based framework. Diffusion coefficients D for such models are often constructed from statistical averages of observed inputs. Here, we use stochastic parameterization to investigate the consequences of temporal variability in D. Variability time scales are constrained using Van Allen Probe observations. Results from stochastic parameterization experiments are compared with experiments using D constructed from averaged inputs and an average of observation‐specific D. We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time‐integrated diffusion is the same. Short variability time scale experiments converge with solutions obtained using an averaged observation‐specific D, and both exhibit greater diffusion than experiments using the averaged‐input D. These experiments reveal the importance of temporal variability in radiation belt diffusion.
Highlights
Physics-based radiation belt models of electron behavior often focus on the wave-particle interactions that accelerate and scatter particles or contribute to radial diffusion
We find that the evolution and final state of the numerical experiment depends upon the variability time scale of D; experiments with longer variability time scales differ from those with shorter time scales, even when the time-integrated diffusion is the same
We have presented the results from a series of idealized numerical experiments that highlight the response of the pitch-angle diffusion equation to temporally varying diffusion coefficients that reproduce the full range of observation-specific wave-particle interactions observed over a 4-year period by NASA Van Allen Probes
Summary
Physics-based radiation belt models of electron behavior often focus on the wave-particle interactions that accelerate and scatter particles or contribute to radial diffusion. These models make considerable use of quasilinear theory to describe the wave-particle interactions (e.g., Lyons et al, 1972; Ripoll et al, 2020) and can be used to study the flux of high-energy electrons on a range of time scales, from single storms (e.g., Allison et al, 2019; Drozdov et al, 2015; Li et al, 2016; Ripoll et al, 2016) to multiple solar cycles (Glauert et al, 2018).
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