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Session 74 - The Quiet & Active Sun.
Display session, Friday, January 09
We present theoretical models of the acceleration and heating of minor ions in the solar wind, as well as detailed anisotropic velocity distribution functions computed numerically by solving the Boltzmann transport equation. We examine the compatibility between these models and spectroscopic measurements of the velocities and kinetic temperatures of various particle species in the solar corona. The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) has measured hydrogen kinetic temperatures in polar coronal holes in excess of 3 million K, and O VI ion kinetic temperatures of at least 200 million K. In addition, the velocity distributions parallel to the open magnetic field are smaller than those perpendicular to the field, possibly implying temperature anisotropy ratios of order 100 for minor ions.
We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfvén waves, which may be the most natural physical mechanism to produce the observed plasma conditions. The modeled ion velocity distributions depend sensitively on the assumed amplitudes and frequencies of the waves, and these computations can be used to accurately predict many quantitative features of the wave power spectrum. Indeed, the more ionic species that are observed spectroscopically, the greater the extent in frequency space the wave spectrum can be inferred.
This work is supported by the National Aeronautics and Space Administration under grant NAG5-3192 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by Swiss funding agencies.
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