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Energetic, relativistic, and ultrarelativistic electrons: Comparison of long-term VERB code simulations with Van Allen Probes measurements

Drozdov A. Y., Y. Y. Shprits, K. G. Orlova, A. C. Kellerman, D. A. Subbotin, D. N. Baker, H. E. Spence, G. D. Reeves, (2015), Energetic, relativistic, and ultrarelativistic electrons: Comparison of long-term VERB code simulations with Van Allen Probes measurements, J. of Geophys. Res. [Space Physics], 120, 3574-3587, doi:10.1002/2014JA020637

Abstract

Abstract In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (>100 keV), relativistic (~0.5–1 MeV), and ultrarelativistic (>2 MeV) electrons. One year of relativistic electron measurements (μ = 700 MeV/G) from 1 October 2012 to 1 October 2013 are well reproduced by the simulation during varying levels of geomagnetic activity. However, for ultrarelativistic energies (μ = 3500 MeV/G), the VERB code simulation overestimates electron fluxes and phase space density. These results indicate that an additional loss mechanism is operational and efficient for these high energies. The most likely mechanism for explaining the observed loss at ultrarelativistic energies is scattering by the electromagnetic ion cyclotron waves.

Authors (sorted by name)

Baker Drozdov Kellerman Orlova Reeves Shprits Spence

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

The authors used geomagnetic indices provided by OMNIWeb (http://omniweb.gsfc.nasa.gov/form/dx1.html) and are grateful to the RBSP‐ECT team for the provision of Van Allen Probes observations (http://www.rbsp‐ect.lanl.gov/). We acknowledge S.G. Claudepierre and J.B. Blake for their helpful discussion. The diffusion coefficients used in the VERB code are available on the Space Environment Modeling Group website (ftp://rbm.epss.ucla.edu/). In addition, authors are appreciative of the valuable comments of the reviewers, whose contribution deserves special acknowledgment. The research of K. Orlova was supported by the NASA Living with a Star Jack Eddy Postdoctoral Fellowship Program, administered by the University Corporation for Atmospheric Research. This research was supported by the NSF grant AGS‐1203747, NASA grant NNX13AE34G, and received funding support from the UC Office of the President, UC Lab Fees Research Program grant 12‐LR‐235337.

Grants

12-LR-235337 AGS‐1203747 NNX13AE34G

Bibtex

@article{doi:10.1002/2014JA020637,
author = {Drozdov, A. Y. and Shprits, Y. Y. and Orlova, K. G. and Kellerman, A. C. and Subbotin, D. A. and Baker, D. N. and Spence, H. E. and Reeves, G. D.},
title = {Energetic, relativistic, and ultrarelativistic electrons: Comparison of long-term VERB code simulations with Van Allen Probes measurements},
journal = {Journal of Geophysical Research: Space Physics},
volume = {120},
number = {5},
pages = {3574-3587},
year ={2015},
keywords = {long-term simulation, VERB code, EMIC waves},
doi = {10.1002/2014JA020637},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2014JA020637},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JA020637},
abstract = {Abstract In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (>100 keV), relativistic (~0.5–1 MeV), and ultrarelativistic (>2 MeV) electrons. One year of relativistic electron measurements (μ = 700 MeV/G) from 1 October 2012 to 1 October 2013 are well reproduced by the simulation during varying levels of geomagnetic activity. However, for ultrarelativistic energies (μ = 3500 MeV/G), the VERB code simulation overestimates electron fluxes and phase space density. These results indicate that an additional loss mechanism is operational and efficient for these high energies. The most likely mechanism for explaining the observed loss at ultrarelativistic energies is scattering by the electromagnetic ion cyclotron waves.}
}