Coronal hole diagnostics out to 8Rsun
Abstract
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 Rsun as r(-8) , from 2 to 4 Rsun 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 Rsun, then a plateau until 1.5 Rsun, thereafter a sharp increase until 2 Rsun, finally a more gradual increase reaching 550 km s(-1) at 3.5 Rsun. Our data suggests that the MHD waves responsible for the excess line broadening tends to become non-linear as it reaches 1.2 Rsun.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1999
- Bibcode:
- 1999A&A...349..956D
- Keywords:
-
- WAVES;
- SUN: CORONA;
- SUN: UV RADIATION