Energetic Particle Distributions Measured in the Heliosheath

Details Energetic Particle Distributions Measured in the Heliosheath Energetic Particle Distributions Measured in the Heliosheath

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsh21a..04d&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH21A-04

Other

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

Scientific paper

Voyager 1 (V1; 98 AU, N34 deg.) has been in the heliosheath since 2004.96. Voyager 2 (V2; 79 AU, S27 deg.) remains in the solar wind, but began measuring termination shock precursor particles in late 2004. Intensities and angular distributions of energetic ions (40 keV-20 MeV) and electrons (30 keV-1.5 MeV) measured by V1 in the heliosheath are compared to those measured in the termination foreshock region by both V1 and V2. Angular distributions are characterized by the amplitude and direction of the first-order anisotropy vector and by its projection onto the T- and R-axis of the local RTN coordinate system. Ion angular distributions in the heliosheath have relatively small first-order anisotropies (amplitudes <~0.03 at 200 keV), with comparable R- and T-components. This is in contrast to the large, mainly tangential, first-order anisotropies measured in the termination foreshock. For example, at V1 during 2004, the average T-component of the first- order anisotropy varied from about -0.24 at 40 keV, to -0.42 at 400 keV, to -0.22 at 8 MeV. Ion intensity distributions are characterized by the local logarithmic slope of intensity versus energy. During the period 2005.0-2005.3, the energy spectrum of ions 40 keV-4 MeV evolved, with the spectral slope at 40 keV remaining near -1.5, and that at 4 MeV increasing from about -2 to -1.6. When averaged over the period 2005.30-2006.15, the spectral slope decreases with energy from -1.44 at 40 keV to -1.63 at 4 MeV. Since about 2005.6, radial plasma flow speeds in the heliosheath, as estimated from analysis of 40-53 and 53-85 keV ion angular distributions, have been in the 50-100 km/s range. During 2005.84-2005.96, anisotropies became nearly radial, enabling us to estimate the radial flow speed using each of eight energy channels covering 40 keV-2 MeV. The eight independent flow speed estimates were consistent with one another, to within 10%, yielding an average flow speed of 80 km/s, and providing further evidence that our flow determination algorithm is reliable.

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