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

Borovsky, J. E. and Denton, Michael H. (2009) Electron loss rates from the outer radiation belt caused by the filling of the outer plasmasphere: The calm before the storm. Journal of Geophysical Research, 114 (A11203). pp. 1-12. ISSN 0148-0227

[thumbnail of art_971.pdf]
PDF (art_971.pdf)

Download (535kB)


Measurements from seven 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 ∼4 × 10−4 cm−3 to ∼1 × 10−4 cm−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. This is confirmed by separately measuring the density decay rate for times when the outer plasmasphere is present or absent. 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.

Item Type:
Journal Article
Journal or Publication Title:
Journal of Geophysical Research
Additional Information:
Copyright (2009) American Geophysical Union. Further reproduction or electronic distribution is not permitted
Uncontrolled Keywords:
?? radiation beltplasmasphere dcs-publications-idart-971dcs-publications-creditsionodcs-publications-personnel-id123earth and planetary sciences (miscellaneous)geophysicsatmospheric sciencespace and planetary science ??
ID Code:
Deposited By:
Deposited On:
12 Nov 2009 15:22
Last Modified:
23 Jul 2024 23:11