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Title: Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015

Abstract

Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection-driven event occurred with a Dst (storm time ring current index) value reaching –223 nT. On 22 June 2015 another strong storm (Dst reaching –204 nT) was recorded. These two storms each produced almost total loss of radiation belt high-energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of radiation belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong “butterfly” distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported “impenetrable barrier” at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the radiation belt slot region to reach the inner Van Allen zone. Altogether, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis.

Authors:
 [1];  [1];  [2];  [3];  [3];  [4];  [4];  [1];  [1];  [1];  [5]; ORCiD logo [5];  [6];  [7];  [8]
  1. Univ. of Colorado, Boulder, CO (United States)
  2. Goddard Space Flight Center, NASA, Greenbelt, MD (United States)
  3. MIT Haystack Observatory, Westford, MA (United States)
  4. The Aerospace Corporation, Los Angeles, CA (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  6. Univ. of New Hampshire, Durham, NH (United States)
  7. Univ. of Iowa, Iowa City, IA (United States)
  8. Univ. of Minnesota, Twin Cities, Minneapolis, MN (United States)
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:
1304817
Report Number(s):
LA-UR-16-22086
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 7; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Heliospheric and Magnetospheric Physics

Citation Formats

Baker, Daniel N., Jaynes, A. N., Kanekal, S. G., Foster, J. C., Erickson, P. J., Fennell, J. F., Blake, J. B., Zhao, H., Li, X., Elkington, S. R., Henderson, Michael Gerard, Reeves, G. D., Spence, H. E., Kletzing, C. A., and Wygant, J. R.. Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015. United States: N. p., 2016. Web. doi:10.1002/2016JA022502.
Baker, Daniel N., Jaynes, A. N., Kanekal, S. G., Foster, J. C., Erickson, P. J., Fennell, J. F., Blake, J. B., Zhao, H., Li, X., Elkington, S. R., Henderson, Michael Gerard, Reeves, G. D., Spence, H. E., Kletzing, C. A., & Wygant, J. R.. Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015. United States. doi:10.1002/2016JA022502.
Baker, Daniel N., Jaynes, A. N., Kanekal, S. G., Foster, J. C., Erickson, P. J., Fennell, J. F., Blake, J. B., Zhao, H., Li, X., Elkington, S. R., Henderson, Michael Gerard, Reeves, G. D., Spence, H. E., Kletzing, C. A., and Wygant, J. R.. Fri . "Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015". United States. doi:10.1002/2016JA022502. https://www.osti.gov/servlets/purl/1304817.
@article{osti_1304817,
title = {Highly relativistic radiation belt electron acceleration, transport, and loss: Large solar storm events of March and June 2015},
author = {Baker, Daniel N. and Jaynes, A. N. and Kanekal, S. G. and Foster, J. C. and Erickson, P. J. and Fennell, J. F. and Blake, J. B. and Zhao, H. and Li, X. and Elkington, S. R. and Henderson, Michael Gerard and Reeves, G. D. and Spence, H. E. and Kletzing, C. A. and Wygant, J. R.},
abstractNote = {Two of the largest geomagnetic storms of the last decade were witnessed in 2015. On 17 March 2015, a coronal mass ejection-driven event occurred with a Dst (storm time ring current index) value reaching –223 nT. On 22 June 2015 another strong storm (Dst reaching –204 nT) was recorded. These two storms each produced almost total loss of radiation belt high-energy (E ≳ 1 MeV) electron fluxes. Following the dropouts of radiation belt fluxes there were complex and rather remarkable recoveries of the electrons extending up to nearly 10 MeV in kinetic energy. The energized outer zone electrons showed a rich variety of pitch angle features including strong “butterfly” distributions with deep minima in flux at α = 90°. However, despite strong driving of outer zone earthward radial diffusion in these storms, the previously reported “impenetrable barrier” at L ≈ 2.8 was pushed inward, but not significantly breached, and no E ≳ 2.0 MeV electrons were seen to pass through the radiation belt slot region to reach the inner Van Allen zone. Altogether, these intense storms show a wealth of novel features of acceleration, transport, and loss that are demonstrated in the present detailed analysis.},
doi = {10.1002/2016JA022502},
journal = {Journal of Geophysical Research. Space Physics},
number = 7,
volume = 121,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 2016},
month = {Fri Jul 01 00:00:00 EDT 2016}
}

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Cited by: 22works
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  • Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D diffusion simulation. By quantitatively comparing the observed and simulated electronmore » evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including radial diffusion, the simulation underestimates the observed electron acceleration, while radial diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of radial diffusion and pitch angle and energy diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.« less
  • By examining the compression-induced changes in the electron phase space density and pitch angle distribution observed by two satellites of Van Allen Probes (RBSP-A/B), we find that the relativistic electrons (>2 MeV) outside the heart of outer radiation belt (L*≥5) undergo multiple losses during a storm sudden commencement. The relativistic electron loss mainly occurs in the field-aligned direction (pitch angle α < 30° or >150°), and the flux decay of the field-aligned electrons is independent of the spatial location variations of the two satellites. However, the relativistic electrons in the pitch angle range of 30°–150° increase (decrease) with the decreasingmore » (increasing) geocentric distance (|ΔL|<0.25) of the RBSP-B (RBSP-A) location, and the electron fluxes in the quasi-perpendicular direction display energy-dispersive oscillations in the Pc5 period range (2–10 min). The relativistic electron loss is confirmed by the decrease of electron phase space density at high-L shell after the magnetospheric compressions, and their loss is associated with the intense plasmaspheric hiss, electromagnetic ion cyclotron (EMIC) waves, relativistic electron precipitation (observed by POES/NOAA satellites at 850 km), and magnetic field fluctuations in the Pc5 band. Finally, the intense EMIC waves and whistler mode hiss jointly cause the rapidly pitch angle scattering loss of the relativistic electrons within 10 h. Moreover, the Pc5 ULF waves also lead to the slowly outward radial diffusion of the relativistic electrons in the high-L region with a negative electron phase space density gradient.« less
  • Measurements from 7 spacecraft in geosynchronous orbit are analyzed to determine the decay rate of the number density of the outer electron radiation belt prior to the onset of high-speed-stream-driven geomagnetic storms. Superposed-data analysis is used wan(?) a collection of 124 storms. When there is a calm before the storm, the electron number density decays exponentially before the storm with a 3.4-day e-folding time: beginning about 4 days before storm onset, the density decreases from {approx}4x10{sup -4} cm{sup -3} to {approx}1X 10{sup -4} cm{sup -3}. When there is not a calm before the storm, the number-density decay is very smalLmore » The decay in the number density of radiation-belt electrons is believed to be caused by pitch-angle scattering of electrons into the atmospheric loss cone as the outer plasmasphere fills during the calms. While the radiation-belt electron density decreases, the temperature of the electron radiation belt holds approximately constant, indicating that the electron precipitation occurs equally at all energies. Along with the number density decay, the pressure of the outer electron radiation belt decays and the specific entropy increases. From the measured decay rates, the electron flux to the atmosphere is calculated and that flux is 3 orders of magnitude less than thermal fluxes in the magnetosphere, indicating that the radiation-belt pitch-angle scattering is 3 orders weaker than strong diffusion. Energy fluxes into the atmosphere are calculated and found to be insufficient to produce visible airglow.« less
  • Using the data from neutron monitors and applying various techniques, the parameters of relativistic solar protons (RSPs) outside the magnetosphere are currently being derived by several research groups. Such data, together with direct proton measurements from balloons and spacecraft, allow the determination of particle energy spectra near the Earth's orbit in successive moments of time. Spectra of RSPs in a number of large solar events tend to indicate the existence of multistep acceleration at/near the Sun. In this paper, we study the generation of RSP by neutral current sheet, stochastic, and shock-wave acceleration, within the framework of two-component concepts formore » ground level enhancements (GLEs) of solar cosmic rays (SCRs). Our analysis is extended to large solar events (GLEs) of 1989 September 29, 2000 July 14, 2003 October 28, and 2005 January 20. We found two different particle populations (components) in the relativistic energy range: a prompt component (PC), characterized by an early impulselike intensity increase, hard spectrum and high anisotropy, and a delayed component, presenting a gradual late increase, soft spectrum and low anisotropy. Based on a two-source model for SCR spectrum formation at the Sun, we carried out theoretical calculations of spectra in the sources for both components. We conclude that the processes in neutral current sheet, together with stochastic acceleration in expanding magnetic trap in the solar corona, are able to explain the production of two different relativistic components. Shock acceleration in the presence of coronal mass ejection (CME) fits fairly only the nonrelativistic range of the SCR spectrum, but fails in the description of relativistic proton spectra, especially for the PC.« less
  • The relationship of increases in the intensities of electrons in the outer magnetosphere and large-scale disturbances of the solar wind is studied with measurements of fluxes of energetic (E/sub e/ approx. 1 MeV) electrons made on the satellites Prognoz-6, -7, and Raduga. It is shown that the effect of high-speed solar wind fluxes on the geomagnetosphere involves the acceleration of electrons near the magnetopause and the enhancement of charged-particle transport into the magnetosphere from the boundary.