Changes in the Solar Modulation of Anomalous Cosmic Rays in the Heliosheath

Details Changes in the Solar Modulation of Anomalous Cosmic Rays in the Heliosheath Changes in the Solar Modulation of Anomalous Cosmic Rays in the Heliosheath

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh23c..03s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH23C-03

Physics

[2104] Interplanetary Physics / Cosmic Rays, [2114] Interplanetary Physics / Energetic Particles, [2124] Interplanetary Physics / Heliopause And Solar Wind Termination

Scientific paper

When Voyager 1 and 2 crossed the shock, both observed modulated ACR spectra indicating that the ACR source is elsewhere on the shock or in the heliosheath. Since August 2007, both Voyagers have been in the heliosheath, providing the first measurements of ACR gradients in the inner region of the heliosheath. At high energies, the ACR intensity has been essentially the same at the two spacecraft, but at lower energies there is a positive intensity gradient between Voyager 2 at 90 AU and Voyager 1 at 111 AU corresponding to a radial gradient of 3 %/AU for ~20 MeV/nuc He. The outward radial motion of Voyager 1 at 3.6 AU/year would result in an 11 %/year intensity increase due to such a spatial gradient. However, the ACR He intensity at ~20 MeV/nuc has increased at twice that rate, indicative of a significant temporal change due to declining solar modulation in the heliosheath. Because of the reduced radial speed in the heliosheath plasma, it takes more than two years for the solar wind plasma to flow from the Sun to beyond Voyager 1 and produce changes in modulation in the outer region of the heliosheath. Correlation of changes in the modulation level in the heliosheath with changing properties of the solar wind and interplanetary magnetic field may provide insight into the location of the modulation region and the source of anomalous cosmic rays.

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