Energetic Particle Populations in the Heliosheath Measured at Voyagers 1 and 2

Details Energetic Particle Populations in the Heliosheath Measured at Voyagers 1 and 2 Energetic Particle Populations in the Heliosheath Measured at Voyagers 1 and 2

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh13c..02d&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH13C-02

Physics

2104 Cosmic Rays, 2114 Energetic Particles (7514), 2124 Heliopause And Solar Wind Termination, 7807 Charged Particle Motion And Acceleration, 7845 Particle Acceleration

Scientific paper

Voyagers 1 (V1) and 2 (V2) have been in the inner heliosheath behind the solar wind termination shock (TS) since 2004/351 and 2007/242, respectively. In this report we compare energetic ion (~0.03-20 MeV) and electron (~0.03-1.5 MeV) intensities, energy spectra, and anisotropies, and the variability of these quantities, measured by the Low Energy Charged Particle instruments on V1 (108 AU, N34°) and V2 (87 AU, S28°). Among the results from recent data taken through Aug. 2008 are the following. (1) Starting around 2008/120 at V2, intensities of heliosheath ions above ~1 MeV and electrons above 0.02 MeV began to decrease, reached minima at pre-TS levels around 2008/145, and since then have increased gradually. The largest drop (factor ~10) occurred in electron intensities, which after 1/3 of a year have recovered to only 1/3 of their pre-drop levels. (2) Large intensity depressions associated with the 2008/120 disturbance did not extend to ions below ~1 MeV at V2. However, these lower energy ions did begin to show more rapid intensity fluctuations (time scale ~hours) comparable to those observed soon after the TS crossing. The net effect after 2008/120 on suprathermal ions 0.028-3.5 MeV was a transition of their energy spectrum from a single power-law with spectral index ~1.4, to one with index varying from ~1.2 at 0.04 MeV to ~1.9 at 3 MeV. By contrast, the intensities of ions 0.04- 4.0 MeV at V1 remain flat and steady, and the energy spectrum is well fit by a power-law with spectral index 1.6±0.1. (3) During 2005.5 to 2008.5 at V1, the component of the heliosheath plasma flow velocity in the R-T plane, estimated from analysis of low-energy ion angular distributions, declined slowly in amplitude from 80-100 km/s to 40-60 km/s. The velocity direction also continued to slowly rotate in the R-T plane, as the angle between the flow velocity and the radial direction increased from ~15° in mid-2005 to ~45° in mid-2008. This resulted mainly from a relatively large decrease in the R-component of the velocity from ~80 to 40 km/s, while the T-component remained relatively steady at about -40 km/s.

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