Measurements of intermediate- and high-degree (20 < l <600) p-mode solar oscillation power and energy

Abstract

We present measurements of the total modal power and energy of both intermediate- and high-degree (20< l <600) solar p-mode oscillations which have been corrected to first order for the combined effects of atmospheric seeing, image motion due to imperfect tracking, and the point spread function of our optics. These power and energy estimates have been obtained from an average of 20 separate zonal l - n power spectra, which were obtained from observations obtained at the 60-Foot Solar Tower of the Mt. Wilson Observatory between July 1 and 20, 1988. The raw total power values were obtained from a least-squares fitting of Lorentzian profiles to the p-mode ridges in the average zonal power spectrum. As an initial method of correcting the observed power levels, we adopted the procedure described by Kaufman (1988) and deconvolved measurements of the observed limb profiles from one of our images using two slightly different theoretical unblurred limb profiles in order to obtain two estimates of the modulation transfer function (mtf) of our experiment. The corrected power values which resulted show systematic variations with both frequency and degree which are similar to those obtained by Kaufman. For example, between l = 100 and 600 our corrected power values drop by a factor of at least 4.5, although the magnitude of our correction becomes less certain as the degree is increased above 300. We also convert these power values into estimates of the total energy of the modes to show that the modal energies decrease by a factor of at least 15 over the same range in l. Even given the uncertainty of our correction at the higher degrees, the consistency of the l-dependent decrease in the modal energies with similar results by Kaufman (1990) suggests that, at least above l = 100, the modes are not in energy equipartition with turbulent convective eddies.