Power-law spatial profile in an upstream region of CME-driven interplanetary shock.

We study the density decay profile of energetic particles in the upstream region of an interplanetary shock on 14 Dec 2006 observed by the ACE spacecraft at 1 AU. The spatial decay profile of the energetic particle flux does not exhibit an exponential behavior as expected for the standard diffusive shock acceleration process but a power-law behavior in anomalous or superdiffusive transport. The power-law profiles are observed for not only the energetic ions reported in Sugiyama & Shiota (2011) but also heavier ions of He2+, CNO, and Fe. We observe the relation <Δx2> ∝ tα for α ~ 1.24-1.72, where Δx is the particle displacement within the time scale t, and the bracket denotes an ensemble average. This implies that particle propagation around a near-earth orbit can be intermediate between normal diffusion (α = 1) and ballistic motion (α equals 2). [ABSTRACT FROM AUTHOR]