University of Maryland
Atlantic Building, Room 2400 4:30 PM Monday, November 27, 2006
Coffee, Tea & Snacks 4:15-4:30 PM

Matthew Hill
Johns Hopkins Applied Physics Laboratory

The Tangle of Ion Populations in the Termination Foreshock and Heliosheath

Observations from the Voyager 1 spacecraft reveal several populations of ions near the solar wind termination shock (TS) where once there was expected to be just one, the so called anomalous cosmic rays (ACRs). Upstream in the termination foreshock (TFS) are highly anisotropic termination foreshock particles (TFPs), with measured energies from ~30 keV-50 MeV, and possibly an underlying population of suprathermal particles (STPs), beginning above a few keV. Downstream in the heliosheath (HS) are slowly varying HS particles (HSPs), measured from ~30 keV up to perhaps 100s of MeV. In the HS and TFS there are spectral features at a few MeV, which may be due to a “third source” of particles resulting from details of geometry and/or injection at the TS, perhaps differing up and downstream. The spatial source and physical processes responsible for the existence of the ACR, TFP, STP, HSP and third source populations are unknown, although now with Voyager 2 also in the TFS we are gaining a stereo view of the problem. I will first describe the essential facts about these populations and the associated heliospheric structures and discuss some of the competing models arising to explain them. Then I will delve into observations from the Low Energy Charged Particle experiment of ~40 keV – 1 GeV ions, concentrating on the differential intensity as a function of energy, time, and direction. These evolving spectral and anisotropic observations, along with the elemental composition provide clues about the origin and transport of the energetic particles near the TS.</