Study of the latitudinal dependence of H I Lyman alpha and O VI emission in the solar corona: Evidence for the superradial geometry of the outflow inthe polar coronal holes

We study the latitudinal distribution of the H I Lyman alpha and O VI (103. 2 nm and 103.7 nm) line emission during the period of the Whole Sun Month c ampaign (August 10 to September 8, 1996) when the Sun was close to the mini mum of its activity. The H I Lyman ct and O VI line intensities appeared to be almost constant with latitude within the polar coronal holes and have a brupt increases toward the streamer region. We found that both north and so uth polar coronal holes had similar line intensities and line-of-sight velo cities, as well as kinetic temperatures of H-0 and O5+. Th, dependence of t hese parameters on latitude and radius is provided. We derived boundaries o f the polar coronal holes based on the H I Lyman ct and O VI line intensity distributions for several days during the Whole Sun Month campaign. We fou nd that the polar coronal hole boundaries clearly have a superradial geomet ry with diverging factor f(max) ranging from 6.0 to 7.5, and they are consi stent with boundaries previously derived from the electron density distribu tions. We also found that, in general, they are not symmetric with respect to the heliographic poles, and their size and geometry change over periods of days. The H I Lyman a, O VI (103.2 nm), and the O VI (103.7 nm) line int ensities showed similar boundaries within the uncertainties of our data. We modeled the latitudinal distribution of the H I Lyman a and O VI(103.2 nm and 103.7 nm) line intensities in the south polar coronal hole on August 17 , 1996, assuming the coronal plasma outflow along either purely radial or n onradial flux tubes. A comparison of model predictions with the observed di stributions shows evidence that the outflow velocity vectors follow nonradi al intensity pattern.