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Analysis of radiation belt energetic electron phase space density using THEMIS SST measurements: Cross-satellite calibration and a case study

Ni B., Y. Shprits, M. Hartinger, V. Angelopoulos, X. Gu, D. Larson, (2011), Analysis of radiation belt energetic electron phase space density using THEMIS SST measurements: Cross-satellite calibration and a case study, J. of Geophys. Res. [Space Physics], 116, doi:10.1029/2010JA016104

Abstract

In this study we perform an energy channel dependent cross-satellite calibration of Time History of Events and Macroscale Interactions during Substorms (THEMIS) solid state telescope (SST) flux measurements based on electron phase space density (PSD) conjunctions at fixed phase space coordinates. By comparing PSD around L* = 6 between THEMIS SST and Los Alamos National Laboratory (LANL) satellite LANL-01A synchronous orbit particle analyzer (SOPA) for a half year period starting from 1 July 2007, we evaluate systematic errors in the THEMIS SST measurements and quantify the cross-instrument calibration factors for the 11 SST energy channels from 40 to 2159 keV. Good consistency in electron PSD conjunctions between the five THEMIS probes indicates that the SST instrument aboard each spacecraft responds quite similarly to the ambient electron radiation environment. Compared to the LANL-01A SOPA instrument, the THEMIS SST underestimates the electron fluxes within a factor of 2 for the 40–140 keV energy channels and overestimates the electron fluxes within a factor of 3 for the 204–2159 keV energy channels. Using the cross-satellite calibrated SST flux data for the five THEMIS spacecraft and the SOPA measurements from the LANL-01A and 1989–048 satellites, we analyze the response of radiation belt electrons to a sudden solar wind pressure enhancement event. The electron PSD conjunctions between the THEMIS probes and the two geostationary satellites show good agreement, suggesting a reasonable cross-satellite calibration of the SST measurements. Our results also indicate a clear correlation between electron PSD dropouts and the solar wind pressure pulse, which is likely due to the combination of magnetopause shadowing and outward radial diffusion. The gradual buildup of electron PSD after the abrupt pressure enhancement most likely results from a combined effect of local acceleration and inward and outward radial diffusion that refills the main phase PSD dropout when the magnetopause moves outward. A longer-term quantitative analysis of the temporal evolution and radial profile of electron PSD based on multiple satellite measurements, including the cross-satellite calibrated THEMIS SST data, will be required to improve our understanding of the dynamic responses of radiation belt electrons to solar activity.

Authors (sorted by name)

Angelopoulos Gu Hartinger Larson Ni Shprits

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

We thank Amanda Leung for help with the calculations of L* and the developers of the ONERA‐DESP library, including D. Boscher, S. Bourdarie, P. O'Brien, and T. Guild. We also thank Reiner Friedel for providing the LANL SOPA data and Yue Chen for helpful discussion. This work was supported by the Lab Research Fee grant 09‐LR‐04‐116720‐SHPY.

Grants

09‐LR‐04116720

Bibtex

@article{doi:10.1029/2010JA016104,
author = {Ni, Binbin and Shprits, Yuri and Hartinger, Michael and Angelopoulos, Vassilis and Gu, Xudong and Larson, Davin},
title = {Analysis of radiation belt energetic electron phase space density using THEMIS SST measurements: Cross-satellite calibration and a case study},
journal = {Journal of Geophysical Research: Space Physics},
year = {2011},
volume = {116},
number = {A3},
pages = {},
keywords = {radiation belt electrons, phase space density, cross-satellite calibration, solar wind dynamic pressure, magnetopause shadowing, radial diffusion},
doi = {10.1029/2010JA016104},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2010JA016104},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JA016104},
abstract = {In this study we perform an energy channel dependent cross-satellite calibration of Time History of Events and Macroscale Interactions during Substorms (THEMIS) solid state telescope (SST) flux measurements based on electron phase space density (PSD) conjunctions at fixed phase space coordinates. By comparing PSD around L* = 6 between THEMIS SST and Los Alamos National Laboratory (LANL) satellite LANL-01A synchronous orbit particle analyzer (SOPA) for a half year period starting from 1 July 2007, we evaluate systematic errors in the THEMIS SST measurements and quantify the cross-instrument calibration factors for the 11 SST energy channels from 40 to 2159 keV. Good consistency in electron PSD conjunctions between the five THEMIS probes indicates that the SST instrument aboard each spacecraft responds quite similarly to the ambient electron radiation environment. Compared to the LANL-01A SOPA instrument, the THEMIS SST underestimates the electron fluxes within a factor of 2 for the 40–140 keV energy channels and overestimates the electron fluxes within a factor of 3 for the 204–2159 keV energy channels. Using the cross-satellite calibrated SST flux data for the five THEMIS spacecraft and the SOPA measurements from the LANL-01A and 1989–048 satellites, we analyze the response of radiation belt electrons to a sudden solar wind pressure enhancement event. The electron PSD conjunctions between the THEMIS probes and the two geostationary satellites show good agreement, suggesting a reasonable cross-satellite calibration of the SST measurements. Our results also indicate a clear correlation between electron PSD dropouts and the solar wind pressure pulse, which is likely due to the combination of magnetopause shadowing and outward radial diffusion. The gradual buildup of electron PSD after the abrupt pressure enhancement most likely results from a combined effect of local acceleration and inward and outward radial diffusion that refills the main phase PSD dropout when the magnetopause moves outward. A longer-term quantitative analysis of the temporal evolution and radial profile of electron PSD based on multiple satellite measurements, including the cross-satellite calibrated THEMIS SST data, will be required to improve our understanding of the dynamic responses of radiation belt electrons to solar activity.}
}