Open AccessSCATHA measurements of electron decay times at 5 < L ≤ 8
Author(s) -
Su YiJiun,
Johnston W. R.,
Albert J. M.,
Ginet G. P.,
Starks M. J.,
Roth C. J.
Publication year - 2012
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2012ja017685
Subject(s) - pitch angle , electron , van allen radiation belt , physics , van allen probes , diffusion , atomic physics , radiation , energy (signal processing) , geosynchronous orbit , computational physics , satellite , magnetosphere , nuclear physics , plasma , geophysics , astronomy , quantum mechanics , thermodynamics
The electron decay timescale ( τ ) is well known to be associated with radiation belt loss processes. Knowledge of τ is important for understanding pitch angle and radial diffusion mechanisms. Previous studies reported decay timescales from the inner belt to geosynchronous orbits; however, relatively few statistical studies have been focused on the region beyond the traditional outer belt. In this paper, a systematic calculation of electron decay times at 5 < L ≤ 8 is performed using 11 years (1979–1989) of electron data from the Spacecraft Charging AT High Altitudes (SCATHA) satellite. The decay timescale is determined using daily median fluxes, providing resolution of τ > 1 day. τ is examined as a function of energy, pitch angle, L shell, Kp , and AE during magnetically disturbed periods when Dst ≤ −50 nT. Results show that τ increases with increasing electron energy at L < 6.6 for electron energies from 50 to 300 keV, but is independent of energy at L > 6.6. This suggests radial transport as the dominant effect at L > 6.6. Additionally, τ decreases with increasing L ‐shell. This dependence has the strongest correlation and is seen in all energies and pitch angles. However, τ has no systematic dependence with pitch angle suggesting that pitch angle diffusion also plays a key role in the electron loss process. Based on our results, τ can be expressed as a function of energy and L , and coefficients are provided for a two‐variable fit. Surprisingly, τ is slightly longer for higher activity cases at L < 6.6, which is inconsistent with the current radial or pitch angle diffusion models. Global effective decay times on the timescale of days place an upper bound on the true loss timescale.