HR: 14:20h
AN: SH43A-02 INVITED     [Abstracts]
TI: Energetic Particles at Voyager 1 in the Heliosheath and Voyager 2 in the Termination Foreshock
AU: * Decker, R B
EM: robert.decker@jhuapl.edu
AF: Johns Hopkins Univ. Applied Physics Lab., 11100 Johns Hopkins Rd, Laurel, MD 20723- 6099, United States
AU: Krimigis, S M
AF: Johns Hopkins Univ. Applied Physics Lab., 11100 Johns Hopkins Rd, Laurel, MD 20723- 6099, United States
AU: Roelof, E C
AF: Johns Hopkins Univ. Applied Physics Lab., 11100 Johns Hopkins Rd, Laurel, MD 20723- 6099, United States
AB: As of 2007.16, Voyager 1 (V1) is in the heliosheath (HSH), having moved radially outward 8 AU since crossing the termination shock (TS) at 94 AU in late 2004 (V1 is at 102 AU, N34° lat., 173° long.). Voyager 2 (V2) is upstream of the TS in its foreshock (TFS) region (V2 is at 82 AU, S27° lat., 216° long.). We discuss variations of intensities and angular distributions of ions >40 keV and electrons >30 keV measured by the LECP instruments on V1 and V2. Measurements made in the TFS region are characterized by large intensity variations, by factors >10, that occur over a range of time scales, from a few hours to tens of days. TFS ion angular distributions often show unidirectional, or beamlike, anisotropies consistent with propagation along the solar wind magnetic field from the source region (i.e., from the TS and the HSH) to the spacecraft under relatively weak-scattering conditions. Notable differences between the V1 and V2 data in the TFS include (1) ion beaming directions that are oppositely directed at the two spacecraft, which may result from the different locations of the two spacecraft relative to an asymmetric TS, and (2) the TFS ion energy spectrum at V2 extends down only to about 0.2 MeV, while that at V1 extends down to at least 0.04 MeV. Data from V1 taken in the HSH are characterized by high intensities of low-energy ions that remain fairly steady, varying by factors <2, and by anisotropies produced mainly by convection at the HSH plasma flow velocity. V1 was crossed by the TS as the shock moved radially inward in late 2004. As a result, conditions in the HSH at V1 were highly disturbed until about mid-2005. Thereafter, the plasma flow velocity V in the HSH, estimated by analysis of low-energy ion angular distributions, has shown mean speed ~ 70 km/s and direction angle ~ -35° to the radial, i.e., on average V_R ~ 58 km/s and V_T ~ -40 km/s (in RTN coordinates). Also, during the past six months, the energy spectrum at V1 of ions 0.04 to ~1 MeV shows a persistent softening with energy, with the spectral index decreasing smoothly from 1.5 at 0.04 MeV to 1.7 at ~1 MeV.
DE: 2104 Cosmic rays
DE: 2114 Energetic particles (7514)
DE: 2124 Heliopause and solar wind termination
DE: 2139 Interplanetary shocks
DE: 7807 Charged particle motion and acceleration
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Joint Assembly