Large Increases of Low-Energy Ion Intensities at Voyager 1 (85 AU) in Mid-2002: Association with Solar Activity in Late-2001

Details Large Increases of Low-Energy Ion Intensities at Voyager 1 (85 AU) in Mid-2002: Association with Solar Activity in Late-2001 Large Increases of Low-Energy Ion Intensities at Voyager 1 (85 AU) in Mid-2002: Association with Solar Activity in Late-2001

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh11a0386d&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH11A-0386

Physics

2111 Ejecta, Driver Gases, And Magnetic Clouds, 2114 Energetic Particles, Heliospheric (7514), 2139 Interplanetary Shocks, 7807 Charged Particle Motion And Acceleration, 7851 Shock Waves

Scientific paper

We report on observations of relatively large intensity increases of low-energy ions (~30 keV to ~10 MeV) that began at Voyager 1 in July 2002. At this time Voyagers 1 and 2 were at respective helioradii 85 AU and 68 AU, and at heliographic latitudes 34°N and 24°S. We use data from the Low Energy Charged Particle (LECP) instruments on each spacecraft. Thus far during the mid-2002 event (which was still evolving when this abstract was written), peak intensities of protons 0.6-1.8 MeV and 3-17 MeV have reached ~10% and ~30%, respectively, those observed by Voyager 1 in association with the powerful GMIR-driven shock in late-1991, when the spacecraft was at 45 AU (i.e., half as far from the Sun). The intensity increases at Voyager 1 are relatively rapid (~few days) and nearly coincident for ion energies from at least 30 keV to several MeV. This is strong evidence that the intensity increases arose from local acceleration at a heliospheric shock, probably that driven by an MIR formed by coalescence of ejecta from enhanced solar activity during the period October-November 2001. An estimate of the disturbance's average radial speed during the ~8-9 months it took to reach 85 AU is then ~600-550 km/s. In contrast to the situation at Voyager 1, energetic ion intensities at Voyager 2 have remained at relatively low levels during 2002. There is no evidence that the disturbance that began passage by Voyager 1 in July passed Voyager 2 ~1-2 months earlier, as one might expect for a uniformly expanding spherical disturbance. The disturbance is evidently non-spherical and is confined mainly to latitudes well north of Voyager 2. This is consistent with observations made in the inner heliosphere. The October-November 2001 solar activity produced high intensities of energetic ions not only near the ecliptic at 1 AU, but also at Ulysses, which was at ~2 AU and above ~70°N heliographic latitude during this period. We will discuss the Voyager 1 low-energy ion data, including angular distributions. We will also describe the effects, if any, of the disturbance on higher energy ions (e.g., Forbush decreases); however, such effects have yet to appear in the evolving intensity profiles.

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