Composition and Spectral Evolution of Energetic Ions at Voyager 1 in the Vicinity of the Solar Wind Termination Boundary

Details Composition and Spectral Evolution of Energetic Ions at Voyager 1 in the Vicinity of the Solar Wind Termination Boundary Composition and Spectral Evolution of Energetic Ions at Voyager 1 in the Vicinity of the Solar Wind Termination Boundary

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11c1121h&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH11C-1121

Other

2104 Cosmic Rays, 2114 Energetic Particles, Heliospheric (7514), 2124 Heliopause And Solar Wind Termination, 7859 Transport Processes

Scientific paper

For a six-month period beginning in mid-2002, measurements from the Low Energy Charged Particle (LECP) instrument aboard Voyager 1 (V1) indicate that the spacecraft was in a region having a low, subsonic solar wind speed. Before and after this period of interest (POI), the observations indicate higher, supersonic solar wind speeds. During the POI there was a low-energy particle enhancement showing intensity increases up to two orders of magnitude over the preceding period, with a composition that is poor in C, and for which the relative intensities of He and O are consistent with anomalous cosmic ray (ACR) composition. Consistency with ACR composition is determined based on ``species scaling'' arguments associated with transport effects. However, since the ACR peak for H is obscured by galactic cosmic rays, the relative H composition is uncertain and may diverge from ACR levels at higher energies per nucleon or may indeed differ from ACR-like composition. We have argued that these and other observations offer evidence that V1 crossed the termination shock (TS), resided downstream of the TS in the heliosheath for about six months, and then re-crossed the TS (which has a variable position), thus reentering the region of supersonic solar wind plasma early in 2003. To investigate this event further, we are undertaking analysis on time scales shorter than the entire six-month period, including the investigation of energy spectra using higher temporal resolution. The noted difference between the expected idealized TS spectrum and that which we observe is reduced when shorter time intervals are examined. There are also possible spectral features indicative of the transport of a very local ACR-like population from the TS to V1 in the upstream region just before and after the POI. Using the LECP instrument, which affords the lowest energy particle measurements from V1, we will pursue the ion composition by considering, e.g., the species scaling in light of the possible temporal or piece-wise rigidity dependence of the mean free path length. We will also analyze the spectral evolution before, during, and after the POI on as fine a temporal scale as statistical limitations will allow.

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