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Title: Acceleration and loss of relativistic electrons during small geomagnetic storms

Abstract

We report that past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms (Dst >₋50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result in flux depletion than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. Small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.

Authors:
 [1];  [1];  [2];  [2]
  1. Dartmouth College, Hanover, NH (United States). Dept. of Physics and Astronomy
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Space Science and Applications; New Mexico Consortium, Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1263497
Alternate Identifier(s):
OSTI ID: 1321769
Report Number(s):
LA-UR-15-28734
Journal ID: ISSN 0094-8276
Grant/Contract Number:
NNX08AM58G; AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 42; Journal Issue: 23; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; radiation belt dynamics; solar wind; geomagnetic storms; geosynchronous relativistic electron flux; heliospheric and magnetospheric physics

Citation Formats

Anderson, B. R., Millan, R. M., Reeves, G. D., and Friedel, R. H. W. Acceleration and loss of relativistic electrons during small geomagnetic storms. United States: N. p., 2015. Web. doi:10.1002/2015GL066376.
Anderson, B. R., Millan, R. M., Reeves, G. D., & Friedel, R. H. W. Acceleration and loss of relativistic electrons during small geomagnetic storms. United States. doi:10.1002/2015GL066376.
Anderson, B. R., Millan, R. M., Reeves, G. D., and Friedel, R. H. W. Wed . "Acceleration and loss of relativistic electrons during small geomagnetic storms". United States. doi:10.1002/2015GL066376. https://www.osti.gov/servlets/purl/1263497.
@article{osti_1263497,
title = {Acceleration and loss of relativistic electrons during small geomagnetic storms},
author = {Anderson, B. R. and Millan, R. M. and Reeves, G. D. and Friedel, R. H. W.},
abstractNote = {We report that past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms (Dst >₋50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result in flux depletion than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. Small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.},
doi = {10.1002/2015GL066376},
journal = {Geophysical Research Letters},
number = 23,
volume = 42,
place = {United States},
year = {Wed Dec 02 00:00:00 EST 2015},
month = {Wed Dec 02 00:00:00 EST 2015}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 13works
Citation information provided by
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  • Past studies of radiation belt relativistic electrons have favored active storm time periods, while the effects of small geomagnetic storms (Dst > –50 nT) have not been statistically characterized. In this timely study, given the current weak solar cycle, we identify 342 small storms from 1989 through 2000 and quantify the corresponding change in relativistic electron flux at geosynchronous orbit. Surprisingly, small storms can be equally as effective as large storms at enhancing and depleting fluxes. Slight differences exist, as small storms are 10% less likely to result in flux enhancement and 10% more likely to result in flux depletionmore » than large storms. Nevertheless, it is clear that neither acceleration nor loss mechanisms scale with storm drivers as would be expected. As a result, small geomagnetic storms play a significant role in radiation belt relativistic electron dynamics and provide opportunities to gain new insights into the complex balance of acceleration and loss processes.« less
  • The x rays produced by electron precipitation from the geomagnetic field have been further studied by means of scintillation counters carried on balloons launched simultaneously at four sites between Waterloo, Iowa, and Flin Flon, Manitoba, Canada. The latitude and detailed time profile were measured during two magnetic storms on September 25, 1961, and Octobor 1, 1981. The integrated photons per centimeter/sup 2/ for the two storms show very different latitude profiles. On September 25 the intensity increased to the highest latitude (64.5 deg geomagnetic). On October 1 the profile was highest at 55 deg and dropped off to a verymore » low value at the high latitude. These differences seem connected with the fact that the September storm was of the recurrent type, and the October 1 storm was more violent and was induced by a large solar flare. The detailed comparison with the total energy stored in the magnetic field, obtained from recent measurements of the trapped radiation in the energy range comparable with the balloon measurements, shows ihat about one or two orders of magnitude more energy was precipitated than in normally stored quiescently, indicating that during the magnetic disturbance the addition of energy to the electrons in the magnetic field is necessary. A more extreme case, observed on July 16, 1961, at Fort Churchill and at Minneapolis, shows that during a strong magnetic sudden impulse more than two orders of magnitude more energy was precipitated than is quiescently trapped. The precipitation has been observed with the data averaged in time intervals between 120 sec and 0.1 sec. We find that during periods of intense precipitation a large fraction of the precipitation occurs in bursts of high intensity lasting only 0.1 sec. It is suggested that these rapid bursts can account for the flashes or pulsations observed in strong auroral storms. Power spectrum analysis methods have been applied to the counting rate data, and we find periodic precipitation occurring with periods of 0.8, 1.6, and 3.2 sec and higher multiples. It is suggested that this constitutes direct evidence for particle bunches near 80-kev energy oscillating between conjugate points in the geomagnetic field. A Chree analysis applied with the large impulsive bursts as zero epoch confirms this picture and shows that the same periods occur in fixed phase relationship to the bursts. (auth)« less
  • Based on comprehensive measurements from Helium, Oxygen, Proton, and Electron Mass Spectrometer Ion Spectrometer, Relativistic Electron-Proton Telescope, and Radiation Belt Storm Probes Ion Composition Experiment instruments on the Van Allen Probes, comparative studies of ring current electrons and ions are performed and the role of energetic electrons in the ring current dynamics is investigated. The deep injections of tens to hundreds of keV electrons and tens of keV protons into the inner magnetosphere occur frequently; after the injections the electrons decay slowly in the inner belt but protons in the low L region decay very fast. Intriguing similarities between lowermore » energy protons and higher-energy electrons are also found. The evolution of ring current electron and ion energy densities and energy content are examined in detail during two geomagnetic storms, one moderate and one intense. Here, the results show that the contribution of ring current electrons to the ring current energy content is much smaller than that of ring current ions (up to ~12% for the moderate storm and ~7% for the intense storm), and <35 keV electrons dominate the ring current electron energy content at the storm main phases. Though the electron energy content is usually much smaller than that of ions, the enhancement of ring current electron energy content during the moderate storm can get to ~30% of that of ring current ions, indicating a more dynamic feature of ring current electrons and important role of electrons in the ring current buildup. Lastly, the ring current electron energy density is also shown to be higher at midnight and dawn while lower at noon and dusk.« less