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Title: Statistical properties of the radiation belt seed population

Abstract

Here, we present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular, we investigate the relationship between the tens and hundreds of keV seed electrons and >1 MeV core radiation belt electron population. Using a cross-correlation analysis, we find that the seed and core populations are well correlated with a coefficient of ≈0.73 with a time lag of 10–15 h. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of hundreds of keV electrons is only one of several conditions required for MeV electron radiation belt acceleration.

Authors:
 [1];  [2];  [2]; ORCiD logo [3];  [4];  [5];  [5];  [5];  [5];  [6]
  1. Univ. of New Hampshire, Durham, NH (United States). Inst. for the Study of Earth, Oceans, and Space; New Mexico Consortium, Los Alamos, NM (United States)
  2. Univ. of New Hampshire, Durham, NH (United States). Inst. for the Study of Earth, Oceans, and Space
  3. New Mexico Consortium, Los Alamos, NM (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  4. Univ. of Colorado, Boulder, CO (United States). Lab. for Atmospheric and Space Physics
  5. Aerospace Corporation, El Segundo, CA (United States). Space Sciences Dept.
  6. Univ. of California, Los Angeles, CA (United States). Dept. of Earth, Planetary, and Space Sciences; Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Earth, Atmospheric, and Planetary Sciences; Univ. of Potsdam (Germany). Helmholtz Centre Potsdam, German Research Centre For Geosciences (GFZ)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
National Aeronautic and Space Administration (NASA); USDOE
OSTI Identifier:
1402613
Report Number(s):
LA-UR-16-23144
Journal ID: ISSN 2169-9380; TRN: US1703010
Grant/Contract Number:
AC52-06NA25396; NAS5-01072
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 8; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 79 ASTRONOMY AND ASTROPHYSICS; Heliospheric and Magnetospheric Physics; radiation belt; seed population; phase space density

Citation Formats

Boyd, A. J., Spence, H. E., Huang, C. -L., Reeves, G. D., Baker, D. N., Turner, D. L., Claudepierre, S. G., Fennell, J. F., Blake, J. B., and Shprits, Y. Y.. Statistical properties of the radiation belt seed population. United States: N. p., 2016. Web. doi:10.1002/2016JA022652.
Boyd, A. J., Spence, H. E., Huang, C. -L., Reeves, G. D., Baker, D. N., Turner, D. L., Claudepierre, S. G., Fennell, J. F., Blake, J. B., & Shprits, Y. Y.. Statistical properties of the radiation belt seed population. United States. doi:10.1002/2016JA022652.
Boyd, A. J., Spence, H. E., Huang, C. -L., Reeves, G. D., Baker, D. N., Turner, D. L., Claudepierre, S. G., Fennell, J. F., Blake, J. B., and Shprits, Y. Y.. 2016. "Statistical properties of the radiation belt seed population". United States. doi:10.1002/2016JA022652. https://www.osti.gov/servlets/purl/1402613.
@article{osti_1402613,
title = {Statistical properties of the radiation belt seed population},
author = {Boyd, A. J. and Spence, H. E. and Huang, C. -L. and Reeves, G. D. and Baker, D. N. and Turner, D. L. and Claudepierre, S. G. and Fennell, J. F. and Blake, J. B. and Shprits, Y. Y.},
abstractNote = {Here, we present a statistical analysis of phase space density data from the first 26 months of the Van Allen Probes mission. In particular, we investigate the relationship between the tens and hundreds of keV seed electrons and >1 MeV core radiation belt electron population. Using a cross-correlation analysis, we find that the seed and core populations are well correlated with a coefficient of ≈0.73 with a time lag of 10–15 h. We present evidence of a seed population threshold that is necessary for subsequent acceleration. The depth of penetration of the seed population determines the inner boundary of the acceleration process. However, we show that an enhanced seed population alone is not enough to produce acceleration in the higher energies, implying that the seed population of hundreds of keV electrons is only one of several conditions required for MeV electron radiation belt acceleration.},
doi = {10.1002/2016JA022652},
journal = {Journal of Geophysical Research. Space Physics},
number = 8,
volume = 121,
place = {United States},
year = 2016,
month = 7
}

Journal Article:
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  • Using the Van Allen Probes data, we study the radiation belt seed population and it associated with the relativistic electron dynamics during 74 geomagnetic storm events. Based on the flux changes of 1 MeV electrons before and after the storm peak, these storm events are divided into two groups of “non-preconditioned” and “preconditioned”. The statistical study shows that the storm intensity is of significant importance for the distribution of the seed population (336 keV electrons) in the outer radiation belt. However, substorm intensity can also be important to the evolution of the seed population for some geomagnetic storm events. Formore » non-preconditioned storm events, the correlation between the peak fluxes and their L-shell locations of the seed population and relativistic electrons (592 keV, 1.0 MeV, 1.8 MeV, and 2.1 MeV) is consistent with the energy-dependent dynamic processes in the outer radiation belt. For preconditioned storm events, the correlation between the features of the seed population and relativistic electrons is not fully consistent with the energy-dependent processes. It is suggested that the good correlation between the radiation belt seed population and ≤1.0 MeV electrons contributes to the prediction of the evolution of ≤1.0 MeV electrons in the Earth’s outer radiation belt during periods of geomagnetic storms.« less
  • Strong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August–September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13–22more » September, initiated by a short-lived geomagnetic storm and characterized by a long period of primarily northward interplanetary magnetic field (IMF), showed strong depletion of relativistic electrons (including an unprecedented observation of long-lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth and the seed population (hundreds of keV) that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. Furthermore, if any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize.« less
  • Fine resolution measurements from the P78-1 satellite of 68- to 1120-keV electrons trapped at the lower L shell edge of the inner radiation belt have provided additional information on the previous discovery (Imhof and Smith, 1965) of the occurrences of peaks in the energy spectra. In some cases the data have yielded upper limits on the widths of the peaks as small as 26 keV. The energies of the peaks decrease slowly with increasing L value at a rate such that the calculated longitude drift periods remain nearly the same over the full L shell range for which they appear:more » often from approx.1.2 to approx.1.4 but occasionally up to L shells as high as approx.2.2. These peaks are frequently observed at approx.600-km altitude in the more durably trapped electron population having minimum drift altitudes of 100 km or greater and are to be contrasted with peaks in the quasi-trapped electrons precipitating from the inner belt at Lapprox. =(1.5-1.85) that decrease in energy much more rapidly with increasing L value (Imhof et al., 1974, 1978; Vampola and Kuck, 1978). The spectra at the lower edge of the inner belt often contain sharp features which are continually changing, perhaps as a result of new injections and/or redistributions and the rapid loss of trapped electrons due to atmospheric scattering. For the narrow peaks the observed small but significant changes in central energy with L value that maintain a constant longitude drift period are consistent with the previous interpretation of the nearly monoenergetic electrons trapped on a given L shell resulting from a redistribution of electrons trapped on somewhat higher L shells (Imhof et al., 1966; Cladis, 1966). In that hypothesis the energy selectivity was postulated to result from a quasi-resonance process whereby the electrons were accelerated as a result of the geomagnetic fluctuations that had periods comparable to the azimuthal drift periods of the electrons.« less
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