MEASUREMENT OF HYDROGEN VELOCITY DISTRIBUTIONS IN THE EXTENDED SOLAR CORONA

H I Ly alpha spectral line profiles have been measured in polar region s of the solar corona at projected heliocentric heights of 1.8-3.5 R(. ). Observations were made with the Ultraviolet Coronal. Spectrometer o n the Spartan 201 satellite from 16:52 to 04:04 UT on 1993 April 11-12 (south pole) and from 12:28 to 22:09 UT on 1993 April 12 (north pole) . In general, the coronal profiles cannot be accurately curve-fitted w ith a single-Gaussian function. The fits with two Gaussians yield most probable velocities of 158 and 322 km s(-1) (south) and 98 and 266 km s(-1) (north). These parameters vary by less than 10% (1 sigma) over the observed heights. The observations are consistent with a line-of-s ight model that attributes the narrow component to background streamer s and to sites within polar coronal holes or a surrounding diffuse cor ona, and the broad component to the polar coronal holes and/or plumes. This interpretation suggests that there are regions within the observ ed coronal holes that have hydrogen and proton kinetic temperatures of (4-6) x 10(6) K, which is 4-10 times higher than the expected electro n temperatures at the same heights. However, other models with, for ex ample, local non-Maxwellian velocity distributions are also consistent with the observations.