UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona

Details UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona

Jul 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...501l.127k&link_type=abstract

Astrophysical Journal Letters v.501, p.L127

Astronomy and Astrophysics

Astronomy

274

Line: Profiles, Sun: Solar Wind, Sun: Corona, Sun: Uv Radiation

Scientific paper

We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H 0 , and O ^{5+} and the outflow velocity and unresolved most probable velocities for H 0 and O ^{5+} during the period between 1996 November and 1997 April. In this Letter, we compare observations of H I Ly alpha and O VI lambda lambda 1032, 1037 emission lines with spatial models of the plasma parameters, and we iterate for optimal consistency between measured and synthesized observable quantities. The unexpectedly large line widths of H 0 atoms and O ^{5+} ions at most radii are the result of anisotropic velocity distributions, which are not consistent with purely thermal motions or the expected motions from a combination of thermal and transverse wave velocities. Above 2 Rsolar , the observed transverse, most probable speeds for O ^{5+} are significantly larger than the corresponding motions for H 0 , and the outflow velocities of O ^{5+} are also significantly larger than the corresponding velocities of H 0 . We discuss the constraints and implications on various theoretical models of coronal heating and acceleration.

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