Ultraviolet spectroscopy of the extended solar corona is a powerful tool for measuring the properties of protons , electrons , and heavy ions in the accelerating solar wind .
The large coronal holes that expand up from the north and south poles at solar minimum are low-density collisionless regions in which it is possible to detect departures from one-fluid thermal equilibrium .
An accurate characterization of these departures is helpful in identifying the kinetic processes ultimately responsible for coronal heating .
In this paper , Ultraviolet Coronagraph Spectrometer ( UVCS ) measurements of the H I Lyman \alpha line are analyzed to constrain values for the solar wind speed , electron density , electron temperature , proton temperature ( parallel and perpendicular to the magnetic field ) and Alfvén-wave amplitude .
The analysis procedure involves creating a large randomized ensemble of empirical models , simulating their Ly \alpha profiles , and building posterior probability distributions for only the models that agree with the UVCS data .
The resulting temperatures do not exhibit a great deal of radial variation between heliocentric distances of 1.4 and 4 solar radii .
Typical values for the electron , parallel proton , and perpendicular proton temperatures are 1.2 , 1.8 , and 1.9 MK , respectively .
Resulting values for the “ nonthermal ” Alfvén wave amplitude show evidence for weak dissipation , with a total energy-loss rate that agrees well with an independently derived total heating rate for the protons and electrons .
The moderate Alfvén-wave amplitudes appear to resolve some tension in the literature between competing claims of both higher ( undamped ) and lower ( heavily damped ) values .