Coronal Hole Diagnostics out to

Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
emails: jgd@star.arm.ac.uk, lte@star.arm.ac.uk, dipu@star.arm.ac.uk

The Si VIII line width measurements and N_e estimates based on SUMER observations are combined with LASCO and UVCS output to provide an overview of its variations with height above a polar coronal hole. From the combined dataset we find a radial dependence of the electron density, in the range 1-2 $R_{\odot}$ as r^-8, from 2 to 4 $R_{\odot}$ as r^-4 and then as r^-2. Combining the Si VIII half width at 1/e of the peak intensity with the UVCS O VI half width, we find a small increase of the half width from 1 to 1.2 $R_{\odot}$ , then a plateau until 1.5 $R_{\odot}$ , thereafter a sharp increase until 2 $R_{\odot}$ , finally a more gradual increase reaching 550 km s^-1 at 3.5 $R_{\odot}$ . Our data suggests that the MHD waves responsible for the excess line broadening tends to become non-linear as it reaches 1.2 $R_{\odot}$ .

Sun: Corona -Ultraviolet; SOHO-Sun: waves; Sun: Coronal Hole; Sun: Electron Density

Coronal Hole Diagnostics out to $8R_{\odot}$

Abstract: