THE EFFECTS OF SCATTERING ON SOLAR OSCILLATIONS

Acoustic modes are scattered by turbulent velocity fluctuations in the solar convection zone. The strongest scattering occurs near the top o f the acoustic cavity where the mode changes character from propagatin g to evanescent. This layer is located at depth z1 approximately g/ome ga2 below the photosphere. The scattering optical depth tau(s) is of o rder M1(2), where M1 is the Mach number of the energy-bearing eddies a t z1. The corresponding contribution to the line width is gamma(s) app roximately omega.M1(2)/pi(n + 1), where n is the mode's radial order. At the top of the acoustic cavity the correlation time of energy-beari ng eddies is much longer than omega-1. Also, the pressure scale height H and the eddy correlation length LAMBDA are comparable to omega/c, w here c is the sound speed. Thus scattering couples modes of similar om ega and all l and has little effect on the sum of their energies. Obse rvations show that mode energies decline with decreasing n (increasing l) at fixed omega. Consequently, scattering damps p-modes and excites f-modes.