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X. Li, S. R. Habbal (Smithsonian Astrophysical Observatory)
Historically, fast waves were believed to be responsible for the solar wind heating. It was known that fast waves primarily heat electrons in a low-beta electron/proton plasma, such as the inner corona. They have been not paid much attention until recently since both in situ and remote sensing measurements (UVCS/SOHO) found that not only ions are hotter than electrons, they have more than mass-proportional temperatures as well. However, at very oblique propagation, proton fundamental and second harmonic cyclotron damping become dominant. The property of oblique fast waves can also be changed dramatically due to the presence of minor ions. Minor ions can change the wave polarization from left-handed at small wave numbers to right-handed at larger wave numbers depending on the abundance of of minor ions, the wave propagation angle, and the relative flow speed between minor ions and protons. In coronal holes, refraction and velocity shear will naturally change wave vectors oblique even these waves originally are parallel. Subsequently, fast branch waves will heat minor ions preferentially if high frequency fast waves can be generated in coronal holes. It is possible that fast waves play a role in coronal heating and the solar wind acceleration.
The author(s) of this abstract have provided an email address for comments about the abstract: xli@cfa.harvard.edu