CENTER-TO-LIMB LINE-WIDTH MEASUREMENTS OF SOLAR CHROMOSPHERIC, TRANSITION REGION AND CORONAL LINES

Line widths derived from observational data obtained by SUMER onboard SOHO in August 1996 at disk center and at the limb are used to confron t those derived via assuming Alfven and/or magneto-acoustic wave heati ng. The observational data clearly shows a center-to-limb variation in the upper chromospheric and transition region lines, with only a marg inal difference in the coronal lines in the sense of additional broade ning further from disk center. Numerical estimations based on linear M HD, favour the existence of Alfven wave heating over magneto-acoustic heating, although further calculations are required. For example, non- linear effects could change the wave characteristics which in turn can have a major effect on the overall line broadening.