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 confront those derived via assuming Alfvén and/or magneto-acoustic wave heating. The observational data clearly shows a center-to-limb variation in the upper chromospheric and transition region lines, with only a marginal difference in the coronal lines in the sense of additional broadening further from disk center. Numerical estimations based on linear MHD, favour the existence of Alfvén 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.