SH51D-06
Energetic Particle Anisotropies at Voyager 1 in the Local Interstellar Medium and at Voyager 2 in the Heliosheath
Friday, 18 December 2015: 09:15
2011 (Moscone West)
Robert B Decker, Applied Physics Laboratory Johns Hopkins, Space, Laurel, MD, United States, Stamatios M Krimigis, Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, Matthew E Hill, Johns Hopkins University, Laurel, MD, United States and Edmond C Roelof, Johns Hopkins Applied Physics Laboratory, Laurel, United States
Abstract:
We describe angular variations of energetic ion and electron intensities measured by the Low Energy Charged Particle instruments on Voyager 1 in the very local interstellar medium, and for context, at Voyager 2 in the heliosheath. We emphasize measurements made in 2014-2015. At Voyager 1, now at 132 AU and 11 AU beyond the heliopause, intensities of low-energy ions and electrons and of anomalous cosmic rays remain at background levels. Galactic cosmic ray ions continue to show small departures from isotropy, with broad (0.3-0.5 year) episodes of intensity depletions of ions gyrating nearly perpendicular to the magnetic field. Percentage intensity decreases during these depletions, relative to intensities of cosmic rays propagating along the field, peak at -7% in 2013.35, -3% in 2014.50, and at least -4% in 2015.60 (when the most recent data were examined). Two episodes in March-April 2013 and April-May 2014 when cosmic ray ion intensities showed small increases lasting 10-20 days indicate small energy boosts, produced possibly by magnetic disturbances from solar activity entering the interstellar medium [Gurnett et al., Ap. J. 2015]. During these two periods intensities of cosmic rays with pitch angles nearer 90 degrees were increased more than those with pitch angles nearer 0 and 180 degrees. At Voyager 2, now 24 AU beyond the termination shock, intensities of ions >30 keV and electrons >20 keV continue to recover in a step-like fashion from minima reached in early 2013. We reported previously that during the rapid initial recovery from these minima as particle intensities rose at Voyager 2, angular data for ions 30 keV to 30 MeV (i.e., including anomalous cosmic rays) showed strong and long lasting (about 4 months) net streaming away from the heliospheric nose toward the flank. A similar streaming episode lasting about 2 months occurred in early 2015, again during a period when intensities were rapidly increasing.
