Home » Kellerman and Shprits 2012

On the influence of solar wind conditions on the outer-electron radiation belt

Kellerman A. C., Y. Y. Shprits, (2012), On the influence of solar wind conditions on the outer-electron radiation belt, J. of Geophys. Res. [Space Physics], 117, doi:10.1029/2011JA017253

Abstract

The dependence of outer-radiation belt electron fluxes upon solar wind velocity and density is investigated using the OMNI solar wind database and LANL-GEO geosynchronous satellites for a period spanning over 20 years. Two dimensional probability distribution functions (PDF) of the flux-solar wind velocity (Vsw) and flux-solar wind density are calculated for electron energies in the 10's of keV to MeV range. The PDF's are normalized by Vsw and density and reveal new distinct relationships. Triangle-shaped flux-Vsw distributions become non-linear PDF's, and the most probable flux increases with Vsw. The only significant saturation of fluxes observed with an increase in Vsw occurs for the lower energy electron fluxes (31.7 keV). The low energy fluxes exhibit a positive correlation with solar wind density, while mid-to-high energy electron fluxes are anti-correlated with density. The maximum probability in the PDF's depends upon both velocity and density, the probability is higher for larger Vsw, and the maximum probability is larger for a given Vsw than for density. The results indicate that Vsw may be more important for determination of fluxes than density, especially for periods of high Vsw if suitable mixed delay times are applied to each solar wind parameter. It is shown that the source population of relativistic electrons of tens of keV exhibit a 2-D normalized flux-Vsw PDF, which is strikingly similar to that of the relativistic electrons. The findings support a model whereby solar wind velocity drives convective transport of source and seed electrons, to the inner magnetosphere, where local acceleration and subsequent radial diffusion is responsible for the enhanced fluxes. The results of this study also indicate that, statistically, ULF waves driven by dynamic pressure variations may act as a significant cause of loss for electrons in the 100's of keV to MeV range.

Authors (sorted by name)

Kellerman Shprits

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

The research was supported by UCā€LANL Lab Research Fee. The authors would like to thank Reeves et al. [2011] for providing the LANL/GEO data set, and Richard Denton and Zhengui Qin for the OMNI2 solar wind data. The authors would also like to thank Andrei Runov and Drew Turner for useful discussions.

Grants

12-LR-235337

Bibtex

@article{doi:10.1029/2011JA017253,
author = {Kellerman, A. C. and Shprits, Y. Y.},
title = {On the influence of solar wind conditions on the outer-electron radiation belt},
journal = {Journal of Geophysical Research: Space Physics},
volume = {117},
year = {2012},
number = {A5},
pages = {},
keywords = {radiation belt electrons, solar wind density, solar wind velocity},
doi = {10.1029/2011JA017253},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2011JA017253},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JA017253},
abstract = {The dependence of outer-radiation belt electron fluxes upon solar wind velocity and density is investigated using the OMNI solar wind database and LANL-GEO geosynchronous satellites for a period spanning over 20 years. Two dimensional probability distribution functions (PDF) of the flux-solar wind velocity (Vsw) and flux-solar wind density are calculated for electron energies in the 10's of keV to MeV range. The PDF's are normalized by Vsw and density and reveal new distinct relationships. Triangle-shaped flux-Vsw distributions become non-linear PDF's, and the most probable flux increases with Vsw. The only significant saturation of fluxes observed with an increase in Vsw occurs for the lower energy electron fluxes (31.7 keV). The low energy fluxes exhibit a positive correlation with solar wind density, while mid-to-high energy electron fluxes are anti-correlated with density. The maximum probability in the PDF's depends upon both velocity and density, the probability is higher for larger Vsw, and the maximum probability is larger for a given Vsw than for density. The results indicate that Vsw may be more important for determination of fluxes than density, especially for periods of high Vsw if suitable mixed delay times are applied to each solar wind parameter. It is shown that the source population of relativistic electrons of tens of keV exhibit a 2-D normalized flux-Vsw PDF, which is strikingly similar to that of the relativistic electrons. The findings support a model whereby solar wind velocity drives convective transport of source and seed electrons, to the inner magnetosphere, where local acceleration and subsequent radial diffusion is responsible for the enhanced fluxes. The results of this study also indicate that, statistically, ULF waves driven by dynamic pressure variations may act as a significant cause of loss for electrons in the 100's of keV to MeV range.}
}