CHARACTERISTICS OF INTERMEDIATE-DEGREE SOLAR P-MODE LINE WIDTHS

We present measurements of the p-mode line widths over the frequency range (1.87 < nu < 4.93 mHz) and degree range (1 less-than-or-equal-to 1 less-than-or-equal-to 150). These results are based on high-quality spectra obtained from intensity observations made at South Pole at a time of low solar activity (1987.9). The line width is observed to vary with mode frequency and degree. The variation with frequency is consistent with the observations of Libbrecht although our measurements are systematically narrower. The frequency variation has been explained in terms of radiative and convective damping of the modes. The observed variation with degree (at constant v) resolves previous contradictory results and is shown to exceed the S-1 variation that is expected on theoretical grounds. Here S is the travel time of a mode from its lower turning point in the solar interior, to its reflection at the solar surface. The deviations from an S-1 variation prompt us to suggest that there are two possible damping mechanisms, in addition to radiative and convective damping, that affect the modes. One of these mechanisms affects modes with 1 less-than-or-similar-to 40 while the other affects modes with 1 greater-than-or-similar-to 25. We suggest that (1) the extra damping for the high l-modes may be due to the absorption of mode power by active regions, and (2) the extra damping for the low l-modes may be caused by an increased leakage of wave energy into the corona by modes that tunnel through the temperature minimum region.