Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: the calm before the storm

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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 smalL ... continued below

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A11203

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Borovsky, Joseph E & Denton, Michael H January 1, 2009.

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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 smalL 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.

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A11203

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  • Journal Name: Journal of Geophysical Research; Journal Volume: 114; Journal Issue: a11

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  • Report No.: LA-UR-09-00076
  • Report No.: LA-UR-09-76
  • Grant Number: AC52-06NA25396
  • DOI: 10.1029/2009JA014063 | External Link
  • Office of Scientific & Technical Information Report Number: 956478
  • Archival Resource Key: ark:/67531/metadc927261

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  • January 1, 2009

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 12, 2016, 5:48 p.m.

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Borovsky, Joseph E & Denton, Michael H. Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: the calm before the storm, article, January 1, 2009; [New Mexico]. (digital.library.unt.edu/ark:/67531/metadc927261/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.