The Voyagers at the Termination Shock: Low-energy Charged Particle Measurements

Details The Voyagers at the Termination Shock: Low-energy Charged Particle Measurements The Voyagers at the Termination Shock: Low-energy Charged Particle Measurements

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh11a..05d&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH11A-05

Physics

2104 Cosmic Rays, 2114 Energetic Particles (7514), 2124 Heliopause And Solar Wind Termination, 2139 Interplanetary Shocks, 7807 Charged Particle Motion And Acceleration

Scientific paper

As of 06 Sep. 2007, Voyager 2 (V2: 84.7 AU, S27.5°) was upstream of the termination shock (TS) in its foreshock region, and Voyager 1 (V1: 103.8 AU, N34.3°) was downstream in the heliosheath (HSH). We focus on measurements made by the Low Energy Charged Particle Experiments (LECP) on V2 and V1 during the past year. At V1, intensities of ions >0.04 MeV in the HSH remained relatively flat during 2007, varying by factors ≤2. The plasma flow velocity in the R-T plane (the LECP scan plane), estimated from angular distributions of ions in three energy channels 0.04-0.14 MeV, continues to show large variations in speed and azimuth. For example, starting in July 2007, the flow speed began increasing from ~40 km/s, reaching ~100 km/s in the most recent data, with the flow direction rotating from mainly toward +R to mainly toward -T. Recent data from several instruments on V2 indicate that V2 may soon encounter the TS. V2 has been measuring termination foreshock (TFS) particles since at least Jan. 2005, shortly after the TS moved radially inward, crossing V1 at 94.0 AU on 16 Dec. 2004. During its 2.5-year traversal of the TFS (mid-2002 through 2004), V1 measured an energy spectrum of low-energy ions that extended smoothly down to at least 0.04 MeV. In contrast, during the past 2.5 years at V2 (2005 to about mid-2007) the TFS spectrum at V2 has rolled over at ~0.2 MeV, dropping to background below ~0.1 MeV. The V2 ion energy spectrum began to unfold in mid-July 2007, and now is above background at 0.028 MeV, but contains large temporal fluctuations on a scale of hours. In the most recent data, the V2 ion intensities above 0.04 MeV exceed those measured by V1 in the TFS during 2004, and above 0.5 MeV exceed those measured by V1 in the HSH during 2005 onward. The recent V2 data also show impulsive intensity increases of electrons >0.022 MeV. Although ion beaming anisotropies at V2 continue to be directed mostly toward +T (in the usual RTN system), there are short bursts (~few days) toward -T. We will discuss these points in more detail and describe the most recent results.

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