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2003 Fall AGU San Francisco, CA 8 December 2003

Observations of the Anisotropies of Enhanced MeV Ion Fluxes at Voyager 1 at 85 AU A. C. Cummings and E. C. Stone, Caltech L. F. Burlaga, GSFC N. F. Ness , Bartol F. B. McDonald, U. Md. W. R. Webber, NMSU. 2003 Fall AGU San Francisco, CA 8 December 2003. Summary.

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2003 Fall AGU San Francisco, CA 8 December 2003

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  1. Observations of the Anisotropies of Enhanced MeV Ion Fluxes at Voyager 1 at 85 AU A. C. Cummings and E. C. Stone, CaltechL. F. Burlaga, GSFCN. F. Ness, BartolF. B. McDonald, U. Md.W. R. Webber, NMSU 2003 Fall AGU San Francisco, CA 8 December 2003

  2. Summary • Cosmic Ray Subsystem 5-MeV proton flow anisotropies at V1 in 2002/2003 are large, variable, and generally outward along the azimuthal field • Average radial anisotropy for 2002/195-2003/38 is small • In agreement with LECP observations • Could be because V1 was downstream of the termination shock • However, because the radial streaming must be continuous across the shock, the radial streaming upstream of the shock should also be small (Jokipii, Kota, and Merenyi, Ap.J,. 405, 782-786,1993) • ACR spectra do not show spectral unfolding expected if V1 crossed the main portion of the shock (McDonald et al., 2003) • Magnetic field data show no evidence that V1 crossed the termination shock (Burlaga et al., 2003) • In this case, the small radial streaming suggests the particles are coming from the termination shock and not from an interplanetary shock co-moving with the solar wind, for which a convective anisotropy would be observed

  3. CRS instrument on Voyager 1 H2 C D B A 11.25 inches

  4. Boresights of five CRS telescopes on Voyager 1 Note (A+B)/(C+H2) is good indicator of azimuthal flow

  5. 4.1-6 MeV protons during 2002-2003 Black > red => azimuthal flow generally along nominal field line away from solar direction Beams of particles are present ~70% of the time (143 of 208 days have ratios significantly > 1)

  6. 5-parameter model for particle distribution

  7. Model results for 10 days in 2002 Dots are plotted where 2  1. Dark blue blobs show where max flux is. Red blobs are where min flux is. Blue plus signs show magnetic field locations on some of the days. Agreement is good in this stretch of data with good statistics.

  8. Azimuths for selected and unselected data Magnetic field data selected such that estimated uncertainty on polar and azimuth are <20 deg. Particle data selection based on reduced 2of fluxes from 5 telescopes. For large 2 the agreement with magnetic field data is pretty good. Even the “all” particle data show that the flow is generally azimuthal and outward along field line.

  9. 5-parameter model for particle distribution with net radial and azimuthal anisotropy shown

  10. del R = (JR-J-R)/(JR+J-R) del T = (JT-J-T)/(JT+J-T) Equivalent to definition of 1st order anisotropy Particle anisotropies in R & T Radial streaming is near zero in all panels. (Expected Compton-Getting anisotropy for 400 km/s wind is shown as vertical dashed line.) Azimuthal streaming is mostly outward along the nominal field line direction.

  11. He spectra for three periods ACRs are heavily modulated when low energy increase at V1 appears. So, according to current models, V1 would not appear to be at the TS.

  12. Summary • Cosmic Ray Subsystem 5-MeV proton flow anisotropies at V1 in 2002/2003 are large, variable, and generally outward along the azimuthal field • Average radial anisotropy for 2002/195-2003/38 is small • In agreement with LECP observations • Could be because V1 was downstream of the termination shock • However, because the radial streaming must be continuous across the shock, the radial streaming upstream of the shock should also be small (Jokipii, Kota, and Merenyi, Ap.J,. 405, 782-786,1993) • ACR spectra do not show spectral unfolding expected if V1 crossed the main portion of the shock (McDonald et al., 2003) • Magnetic field data show no evidence that V1 crossed the termination shock (Burlaga et al., 2003) • In this case, the small radial streaming suggests the particles are coming from the termination shock and not from an interplanetary shock co-moving with the solar wind, for which a convective anisotropy would be observed

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