Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: the calm before the storm Page: 2 of 31
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Submitted to Journal of Geophysical Research
Electron Loss Rates from the Outer Radiation Belt Caused by the
Filling of the Outer Plasmasphere: The Calm before the Storm
Joseph E. Borovsky' and Michael H. Denton2
1Los Alamos National Laboratory
Abstract. 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 with 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 ~4x 10- cm-3 to ~lx lO~ cm. 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
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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]. (https://digital.library.unt.edu/ark:/67531/metadc927261/m1/2/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.