Energetic Particle Measurements from Voyager 1 in the Heliosheath

Details Energetic Particle Measurements from Voyager 1 in the Heliosheath Energetic Particle Measurements from Voyager 1 in the Heliosheath

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsh43b..05d&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SH43B-05

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

Voyager 1 encountered the solar wind termination shock (TS) on day 351 of 2004 (94.0 AU, N34°) and entered the heliosheath. Since that time until at least day 248 of 2005 (96.6 AU), observations indicate that the spacecraft has remained in the heliosheath. We will describe intensities and angular distributions of ions >40 keV and electrons >26 keV measured during 2005 by the Low Energy Charged Particle instruments on Voyagers 1 and 2. Notable features observed thus far in the heliosheath particle data from Voyager 1 include: (1) high, slowly rising, and relatively smooth intensities devoid of the large (factors ~5-10), frequent (~26 days) fluctuations that characterized intensities upstream of the TS; (2) large reductions in the amplitude and occurrence rates of the anti-sunward, near-azimuthal beaming anisotropies that were routinely seen in the pre-TS ion data; and, (3) radial plasma flow speeds, estimated from analysis of low-energy ion angular distributions, that have ranged over ~+100 km/s (2004.95-2005.04), ~-50 to 0 km/s (2005.04-2005.30), ~0 to +50 km/s (2005.3-2005.46), and most recently ~+50 to +100 km/s (2005.46-2005.66). For about the first 0.5 year after the TS crossing (2004.95), intensities of protons 40 to ~500 keV remained relatively flat, while those of protons >500 keV increased steadily. Starting around 2005.45, however, intensities of the lower energy protons also began increasing, and in the recent data, intensities at all energies >40 keV have leveled off. We are fortunate to be currently receiving heliosheath data from Voyager 1 and solar wind data from Voyager 2, which has evidently entered the termination foreshock region. Voyager 2 began observing low intensities of TS precursor protons in late 2004 (75 AU, S26°), and by mid-2005 (77 AU), both the intensity and anti-sunward, near-azimuthal beaming anisotropy of 3-17 MeV protons had reached levels comparable to those observed at Voyager 1 during the latter half of 2002 (85-87 AU). We will discuss further details of these Voyager 1 and 2 observations made in the vicinity of the TS.

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