Wind SWE observations of proton double streaming and correlations with wave activity

We report on observations of proton double streaming made from the Wind spacecraft by the SWE Faraday Cup detectors. The observations were made near the ecliptic in low-density, slow solar wind on January 12, 2001. Secondary (faster) ion beams appear as an enhanced, higher-energy/charge tail on the proton velocity distributions or as a distinct higher-energy distribution with a clearly defined peak. At times, the number density of the higher-energy component was as large as that of the primary component. A third component with an energy/charge peak consistent with that expected for alpha particles relative to the primary component peak was also seen during portions of the day. Additional evidence that the secondary stream was protons is provided by the fact that under that assumption the velocity difference between the streams lies along the local magnetic field. Generally we find that the relative speed of the streams is less than the local Alfven speed. We also observe that the temperature anisotropy is reversed in the two proton beams, with the parallel thermal speed being consistently greater than the perpendicular thermal speed in the higher-energy/charge beam, whilst the opposite anisotropy is observed in the primary component. Simultaneous measurements made by the WAVES experiment onboard Wind reveal that the appearance of the secondary proton component coincides with increases in the wave activity. The evidence suggests therefore that these double proton beams are either created locally through wave-particle interactions or that the enhanced wave activity is driven by the double streaming itself.