Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsh22a..02d&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SH22A-02
Physics
2114 Energetic Particles, Heliospheric (7514), 2124 Heliopause And Solar Wind Termination, 2139 Interplanetary Shocks, 7807 Charged Particle Motion And Acceleration, 7859 Transport Processes
Scientific paper
The Voyager 1 (V1) spacecraft has observed large variations in ion (40 keV to 30 MeV) and electron (26 keV to 1.5 MeV) intensities, ion energy spectra, and ion angular distributions since at least mid-2002. Comparable phenomena have been not observed at Voyager 2 (66-74 AU, S25°), indicating that V1 (85-94 AU, N34°) has been measuring particles associated with the heliospheric termination shock (TS). We present observations from the Low Energy Charged Particle (LECP) instrument on V1, focusing on data acquired during 2004.1 to ~2005.4. V1 observed a second major episode of sustained increases of energetic particle intensities beginning ~2004.1 and lasting until ~2004.78 (the first major episode occurred during ~2002.6-2003.1). Enhanced ion intensities include superposed small-scale (~few hours) and quasi-recurrent (~13 days) variations, with the larger of these variations exhibiting little or no velocity dispersion over energies from 40 keV to 30 MeV. Ion anisotropies are mainly unidirectional outward (away from the Sun) along the near-azimuthal direction. Large intensity increases of electrons with energies from at least 26 keV to 1.5 MeV occurred during 2004.1-2004.2 and 2004.6-2004.8. As with the ions, these electron increases include small-scale, bursty (~few hours to ~day) components, with the largest peaks time-coincident (non-dispersive) with those of the ions; but, unlike the ions, the electrons have nearly isotropic angular distributions. Particle intensities decreased abruptly on ~2004.78, remained low for roughly 65 days, increased rapidly on ~2004.96, and have remained high until at least 2005.1. A remarkable feature of this latest increase is that the intensities of ions from at least 40 keV to ~350 keV recovered to values well above those reached prior to the late-2004 drop (e.g., factors ~2-3 higher). We will summarize these results and also report on revised estimates of convection speeds that are based upon reanalysis of angular distributions of ions 40 keV to 20 MeV.
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