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ACE News #115 - Sep 26, 2008
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Figure 1 (left): Solar energetic particles observed near 1 AU (solid dot) contain both an injected and a mirrored component. The mirrored component has backscattered beyond 1 AU, mirrored inside 1 AU, and returned to 1 AU. The equation/algorithm (lower right) describes this process. Figure 2 (right) shows an application of our algorithm to extract the actual solar injection history from a near-relativistic (175-300keV) electron event.
The near-light speed and nearly scatter-free propagation out to 1 AU of
175-300 keV electrons preserves the essential details of their injection onto
the interplanetary magnetic field. We have developed a quantitative method
that uses the pitch-angle anisotropies to extract the electron injection
history for near-relativistic beam-like solar electron events well past the
rise-to-maximum phase. As sketched in Fig. 1, this is accomplished by
subtracting from the outgoing electrons at 1AU (j+)
those that have already
back-scattered from beyond 1AU, re-crossed 1AU (j-),
mirrored and finally returned to 1 AU (jm).
The difference between the outgoing intensity (j-)
and that of this
mirrored component, delayed by its mirroring time 2τ inside 1AU,
jm(t) = (j-)(t-2τ),
gives the intensity
j0(t) = js(t-z/v)
of the "first-crossing" electrons that are still arriving directly
from the Sun (js)
after traveling a distance (z) along the field line at velocity (v).
The implementation of the time-shifted algorithm (Fig. 2)
starts from the spin-sectored intensities (different colors) in the three EPAM
heads (top 3 panels).
These sectored data are fit with exponential functions of pitch-angle
This item was contributed by Dennis K Haggerty and Edmond C Roelof (JHUAPL). Address questions and comments to or
Last modified 19 Mar 2008.