Comparison of 40-4000 keV Ion Angular Distributions with Magnetic Field Data Measured by Voyager-1 at 85 AU

Details Comparison of 40-4000 keV Ion Angular Distributions with Magnetic Field Data Measured by Voyager-1 at 85 AU Comparison of 40-4000 keV Ion Angular Distributions with Magnetic Field Data Measured by Voyager-1 at 85 AU

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11c1117d&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH11C-1117

Physics

2114 Energetic Particles, Heliospheric (7514), 2124 Heliopause And Solar Wind Termination, 2134 Interplanetary Magnetic Fields, 2139 Interplanetary Shocks

Scientific paper

During the time period ˜2002.6 to ˜2003.1, Voyager-1 (V1) observed a number of unusual features in the Low Energy Charged Particle (LECP) data in the outer heliosphere not similar to what had been seen previously in the inner heliosphere (Krimigis, et al., this Conference). Among the features measured by the V1 LECP instrument during this ˜0.5-yr. long `event' were (1) sustained periods of large, near-azimuthal, anti-sunward streaming of ions 40-4000 keV, and (2) near-zero convective flow, as deduced by non-linear Compton-Getting analyses of these ion data averaged over the entire event. Feature (2) is analyzed in detail in a companion paper (Roelof et al., this Conference). In the present paper we examine relatively high time-resolution ion angular distributions measured by the V1 LECP during 2002 to ˜2003.8 (83-90 AU, N34o) to determine the time- and energy-dependence of the ion anisotropies observed before, during, and after the event proper. Relevant LECP data include one- and three-day averaged intensities of ions 40-4000 keV that arrive in seven of eight 45o sectors. V1 observed short-lived ( ˜days) intensity increases in early 2002 and mid-2003 with anisotropies that varied rapidly ( ˜hrs) in magnitude and direction, e.g., from field-aligned sunward to field-aligned anti-sunward. It is likely that some of these pre- and post-event structures are precursor ions that propagate to V1 when the interplanetary magnetic field connects the spacecraft to the high-intensity source. During the event itself, ion anisotropies display energy-dependent variations. We express the ion anisotropies in terms of pitch angle by combining the ion angular data during selected periods of the event with magnetic field vector (B) measurements from the V1 Magnetic Field (MAG) instrument. Knowing the field direction, the non-linear Compton-Getting analysis will yield limits on the convection velocity for each given angular distribution. In addition, we can also calculate in the convective frame the parallel and perpendicular pressure components carried by ions 40-4000 keV, and compare these with the measured magnetic field pressure to assess, for instance, whether the streaming energetic particles can be driving a firehose instability.

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