Low-altitude measurements of 2-6 MeV electron trapping lifetimes at 1.5≤ L≤2.5

Abstract

During the Halloween Storm period (October-November 2003), a new Van Allen belt electron population was powerfully accelerated. The inner belt of electrons formed in this process decayed over a period of days to years. We have examined quantitatively the decay rates for electrons seen in the region of 1.5 ≤ L ≤ 2.5 using SAMPEX satellite observations. At L = 1.5 the e-folding lifetime for 2-6 MeV electrons was τ ∼ 180 days. On the other hand, for the half-dozen distinct acceleration (or enhancement) events seen during late-2003 through 2005 at L ∼ 2.0, the lifetimes ranged from τ ∼ 8 days to τ ∼ 35 days. We compare these loss rates to those expected from prior studies. We find that lifetimes at L = 2.0 are much shorter than the average 100-200 days that present theoretical estimates would suggest for the overall L = 2 electron population. Additional wave-particle interaction aspects must be included in theoretical treatments and we describe such possibilities here. Copyright 2007 by the American Geophysical Union.