Reoccurence of enhanced intensities of low-energy particles at Voyager 1 in mid-2003

The >0.5 MeV/nuc ion intensity measured by the Cosmic Ray experiment on Voyager 1 (V1) (at 88.8 AU and 33.9°N) began to show sporadic enhancements above background levels beginning in mid-2003 and in February 2004 exceeded the intensity level during the earlier 2002 event. The intensities at Voyager 2 (V2) (70.6 AU and 24.5°S) do not show a corresponding increase. The 2002 event lasted ∼7 months and was characterized by a low-energy particle intensity increase at V1 by two or more orders of magnitude with no corresponding increase at V2. The origin of this increase at V1 is currently under debate, with some investigators suggesting that the solar wind termination shock was crossed, while others maintain that V1 remained upwind of the shock. The 2002 event has been fairly well characterized in terms of the particle energy spectra and streaming properties. The event ended in early 2003 with the intensities returning to near background levels by 2003.4. We will characterize the energetic particle properties of the new 2003 event and compare with the properties of the 2002 event. This work was supported by NASA under contract NAS7-03001.