Physics
Scientific paper
Apr 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998eostr..79..278c&link_type=abstract
Eos Trans. AGU, 79 (17), Spring Meeting Suppl., S278 (SH42A-11, Invited)
Physics
Solar Corona, Solar Wind, Alfven Waves, Ion Cyclotron Resonance, Uvcs, Soho, Ultraviolet Emission Lines
Scientific paper
We present empirical models based on UVCS/SOHO observational data for several plasma parameters in the fast solar wind emerging from near-solar-minimum polar coronal holes. We also discuss the constraints on various theoretical processes of coronal heating and acceleration, and present preliminary kinetic models of the velocity distributions. UVCS/SOHO has measured hydrogen kinetic temperatures in polar coronal holes in excess of 3 million K, and O5+ ion kinetic temperatures of at least 200 million K. 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. In addition, Doppler dimming and pumping of the emission line intensities indicates that the O5+ ions may have higher outflow velocities than the protons; the ions may reach 500 km/s by a radius of 4 solar radii. We examine various features of plasma heating by the dissipation of high-frequency ion-cyclotron resonance Alfven waves, which may be the most natural physical mechanism to produce the observed plasma conditions. This resonant wave damping produces anisotropic velocity-space diffusion and a significant outward acceleration in addition to that provided to ions by the magnetic mirror force. Because different ions have different resonant frequencies, they receive different amounts of heating and acceleration as a function of radius. Thus, the more ionic species that are observed, the greater the extent in frequency space the wave spectrum can be inferred and spatially mapped.
Cranmer Steven R.
Field George B.
Kohl John L.
Noci Giancarlo
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