Energetic outer zone electron loss timescales during low geomagnetic activity
Article first published online: 27 MAY 2006
Copyright 2006 by the American Geophysical Union.
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 111, Issue A5, May 2006
How to Cite
2006), Energetic outer zone electron loss timescales during low geomagnetic activity, J. Geophys. Res., 111, A05212, doi:10.1029/2005JA011516., , , , , , and (
- Issue published online: 27 MAY 2006
- Article first published online: 27 MAY 2006
- Manuscript Accepted: 9 FEB 2006
- Manuscript Revised: 1 FEB 2006
- Manuscript Received: 3 NOV 2005
- plasmaspheric hiss;
- radiation belts
 Following enhanced magnetic activity the fluxes of energetic electrons in the Earth's outer radiation belt gradually decay to quiet-time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 ≤ L ≤ 5.0 occurs during quiet periods (Kp < 3−) following enhanced magnetic activity on timescales ranging from 1.5 to 3.5 days for 214 keV electrons to 5.5 to 6.5 days for 1.09 MeV electrons. The intervals of decay are associated with large average values of the ratio fpe/fce (>7), indicating that the decay takes place in the plasmasphere. We compute loss timescales for pitch-angle scattering by plasmaspheric hiss using the PADIE code with wave properties based on CRRES observations. The resulting timescales suggest that pitch angle scattering by plasmaspheric hiss propagating at small or intermediate wave normal angles is responsible for electron loss over a wide range of energies and L shells. The region where hiss dominates loss is energy-dependent, ranging from 3.5 ≤ L ≤ 5.0 at 214 keV to 3.0 ≤ L ≤ 4.0 at 1.09 MeV. Plasmaspheric hiss at large wave normal angles does not contribute significantly to the loss rates. At E = 1.09 MeV the loss timescales are overestimated by a factor of ∼5 for 4.5 ≤ L ≤ 5.0. We suggest that resonant wave-particle interactions with EMIC waves, which become important at MeV energies for larger L (L > ∼4.5), may play a significant role in this region.