Transient Shocks and Associated Energetic Particle Distributions Observed by ACE during Cycle 23

Details Transient Shocks and Associated Energetic Particle Distributions Observed by ACE during Cycle 23 Transient Shocks and Associated Energetic Particle Distributions Observed by ACE during Cycle 23

Aug 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aipc.1039..184h&link_type=abstract

PARTICLE ACCELERATION AND TRANSPORT IN THE HELIOSPHERE AND BEYOND: 7th Annual International Astrophysics Conference. AIP Confer

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Magnetohydrodynamics And Plasmas, Planetary Bow Shocks, Interplanetary Shocks, Particle Acceleration, Gravitational Radiation, Magnetic Fields, And Other Observations, Astronomical And Space-Research Instrumentation, Origin, Formation, And Abundances Of The Elements, Spectroscopy And Spectrophotometry

Scientific paper

Characteristics of both interplanetary (IP) shocks and associated energetic particle distributions (e.g., time-intensity profiles, peak intensities, energy spectra indices, etc.) observed near 1 AU during solar active periods are analyzed. From February 1998 through October 2003, the ACE spacecraft (at 1 AU) detected 298 IP shocks (i.e., occurrence rate ~50 IP shocks/year). A subset of 191 IP shocks was identified as transient, fast-forward shocks. We summarize the findings of the statistical survey. Of the 191 sample shocks, 123 (64%) were associated with intensity increases in 47-68 keV ions, 62 (32%) with increases in 1.9-4.8 MeV ions, and 39 (20%) with increases in 38-53 keV electrons, all measured by the EPAM instrument onboard ACE. It is noteworthy that even in the relatively low-energy ion range 47-68 keV, 68 (36%) of the 191 shocks did not produce an observable intensity increase. The 191 shocks were classified according to the temporal evolution of their time-intensity profiles and of their energy spectra indices. Ion spectra indices in the immediate post-shock region of the shocks were compared to spectral indices expected from steady-state diffusive shock-acceleration (DSA) theory. The majority of the measured spectral indices do not agree with the DSA-predicted indices, which depend only upon shock compression ratio. Ion spectra measured at the shock are often softer than the ion spectra measured well upstream of the shock. This suggests that shock interactions of >47 keV ions are weak at 1 AU; consequently, the strong interaction (i.e., multiple shock crossings) description may not apply to most shock events at 1 AU.

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