Abstract
AbstractMany modern outer radiation belt models simulate the long‐time behavior of high‐energy electrons by solving a three‐dimensional Fokker‐Planck equation for the drift‐ and bounce‐averaged electron phase space density that includes radial, pitch‐angle, and energy diffusion. Radial diffusion is an important process, often characterized by a deterministic diffusion coefficient. One widely used parameterization is based on the median of statistical ultralow frequency (ULF) wave power for a particular geomagnetic index Kp. We perform idealized numerical ensemble experiments on radial diffusion, introducing temporal and spatial variability to the diffusion coefficient through stochastic parameterization, constrained by statistical properties of its underlying observations. Our results demonstrate the sensitivity of radial diffusion over a long time period to the full distribution of the radial diffusion coefficient, highlighting that information is lost when only using median ULF wave power. When temporal variability is included, ensembles exhibit greater diffusion with more rapidly varying diffusion coefficients, larger variance of the diffusion coefficients and for distributions with heavier tails. When we introduce spatial variability, the variance in the set of all ensemble solutions increases with larger spatial scales of variability. Our results demonstrate that the variability of diffusion affects the temporal evolution of phase space density in the outer radiation belt. We discuss the need to identify important temporal and length scales to constrain variability in diffusion models. We suggest that the application of stochastic parameterization techniques in the diffusion equation may allow the inclusion of natural variability and uncertainty in modeling of wave‐particle interactions in the inner magnetosphere.
Highlights
The Van Allen outer radiation belt is a typically quiescent torus‐shaped region in near‐Earth space between 13,000 and 40,000 km radial distance consisting mainly of electrons between 100s of keV and multiple MeV trapped by the Earth's geomagnetic field
Our results demonstrate that the variability of diffusion affects the temporal evolution of phase space density in the outer radiation belt
Our results find that better understanding of temporal and spatial variations of ultralow frequency (ULF) wave interactions with electrons, and being able to characterize these variations to a good level of accuracy, is vital to produce a robust description of radial diffusion over long timescales in the outer radiation belt
Summary
The Van Allen outer radiation belt is a typically quiescent torus‐shaped region in near‐Earth space between 13,000 and 40,000 km radial distance consisting mainly of electrons between 100s of keV and multiple MeV trapped by the Earth's geomagnetic field. The behavior of electrons in the outer radiation belt is affected by multiple processes, some of which are immediate responses to solar wind forcing, whereas some are more indirect energy pathways involving energy stored in the substorm cycle. Journal of Geophysical Research: Space Physics radiation belt, allowing us to quantify the effects of different processes (e.g., Glauert et al, 2014; Reeves et al, 2012; Shprits et al, 2008). There remains a pressing need to develop accurate models of the outer radiation belt for operational purposes in addition to promoting further physical understanding
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.