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Responses of Earth's radiation belts to solar wind dynamic pressure variations in 2002 analyzed using multisatellite data and Kalman filtering

Ni B., Y. Y. Shprits, R. H. Friedel, R. M. Thorne, M. Daae, Y. Chen, (2013), Responses of Earth’s radiation belts to solar wind dynamic pressure variations in 2002 analyzed using multisatellite data and Kalman filtering, J. of Geophys. Res. [Space Physics], 118, 4400-4414, doi:10.1002/jgra.50437

Abstract

It has been difficult to establish a definitive causal link between radiation belt electron dropouts and solar wind dynamic pressure, due to adiabatic effects and observations limited to a single location in space at one time. Here we reconstruct the radial profiles of radiation belt electron phase space density (PSD) for the entire year of 2002 (solar maximum), based on a combination of the VERB radial diffusion model and data assimilation of the sparse observations from six satellites including GEO1989, GEO1990, LANL-97A, LANL-01A, GPSns33, and POLAR, to perform a statistical analysis of the potential relationship between electron PSD dropout and solar wind dynamic pressure variation. We capture 59 electron PSD dropout events, 81% associated with solar wind dynamic pressure sudden jumps (i.e., pulses) or modest increase, consistent with the results of Shprits et al. (2012) for the period of 1990–1991. With the continuous availability of high quality solar wind data in 2002, we further identify 41 pressure pulses and determine that 68% of them are associated with electron PSD dropouts. We also identify 49 pressure enhancements, 41% of which are associated with electron PSD dropouts. Our results support that gradual or sharp enhancements in solar wind dynamic pressure can play an important role in producing electron PSD dropouts, owing to inward intrusion of the magnetopause that enhances the loss to the magnetopause and outward radial diffusion. But we conclusively demonstrate that solar wind dynamic pressure pulses and enhancements are neither a necessary nor a sufficient condition for the formation of electron PSD dropouts, which suggests that some other mechanism(s), which remains mysterious, is required to explain electron PSD dropout occurrences without pressure pulse or modest pressure increase. For the first time, we also perform a quantitative comparison of conjunctions between electron PSD reanalysis results and satellite PSD data, which indicates a tolerable and reasonable error in assimilated PSD within a factor of 5. Differences in assimilated PSD and satellite PSD have a potential for use to evaluate the ignored processes in the physical model and to estimate the errors associated with satellite measurements.

Authors (sorted by name)

Chen Friedel Ni Shprits Thorne

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was supported by the Lab Research Fee grant 12‐LR‐235337 and the NASA grants NNX10AK99G and NNX13AE34G. We acknowledge the developers of ONERA‐DESP library, use of NASA/GSFC's Space Physics Data Facility's OMNIWeb service, and OMNI solar wind and geophysical data. We also thank Dmitri Kondrashov for helpful discussions. We thank the reviewers for valuable comments and constructive suggestions.

Grants

12-LR-235337 NNX10AK99G NNX13AE34G

Bibtex

@article{doi:10.1002/jgra.50437,
author = {Ni, Binbin and Shprits, Yuri Y. and Friedel, Reiner H. W. and Thorne, Richard M. and Daae, Marianne and Chen, Yue},
title = {Responses of Earth's radiation belts to solar wind dynamic pressure variations in 2002 analyzed using multisatellite data and Kalman filtering},
journal = {Journal of Geophysical Research: Space Physics},
year = {2013},
volume = {118},
number = {7},
pages = {4400-4414},
keywords = {radiation belt electron phase space density, data assimilation, solar wind dynamic pressure},
doi = {10.1002/jgra.50437},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/jgra.50437},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/jgra.50437},
abstract = {It has been difficult to establish a definitive causal link between radiation belt electron dropouts and solar wind dynamic pressure, due to adiabatic effects and observations limited to a single location in space at one time. Here we reconstruct the radial profiles of radiation belt electron phase space density (PSD) for the entire year of 2002 (solar maximum), based on a combination of the VERB radial diffusion model and data assimilation of the sparse observations from six satellites including GEO1989, GEO1990, LANL-97A, LANL-01A, GPSns33, and POLAR, to perform a statistical analysis of the potential relationship between electron PSD dropout and solar wind dynamic pressure variation. We capture 59 electron PSD dropout events, 81% associated with solar wind dynamic pressure sudden jumps (i.e., pulses) or modest increase, consistent with the results of Shprits et al. (2012) for the period of 1990–1991. With the continuous availability of high quality solar wind data in 2002, we further identify 41 pressure pulses and determine that 68% of them are associated with electron PSD dropouts. We also identify 49 pressure enhancements, 41% of which are associated with electron PSD dropouts. Our results support that gradual or sharp enhancements in solar wind dynamic pressure can play an important role in producing electron PSD dropouts, owing to inward intrusion of the magnetopause that enhances the loss to the magnetopause and outward radial diffusion. But we conclusively demonstrate that solar wind dynamic pressure pulses and enhancements are neither a necessary nor a sufficient condition for the formation of electron PSD dropouts, which suggests that some other mechanism(s), which remains mysterious, is required to explain electron PSD dropout occurrences without pressure pulse or modest pressure increase. For the first time, we also perform a quantitative comparison of conjunctions between electron PSD reanalysis results and satellite PSD data, which indicates a tolerable and reasonable error in assimilated PSD within a factor of 5. Differences in assimilated PSD and satellite PSD have a potential for use to evaluate the ignored processes in the physical model and to estimate the errors associated with satellite measurements.}
}