MODELING OF INTEGRATED SUNLIGHT VELOCITY-MEASUREMENTS - THE EFFECT OFSURFACE DARKENING BY MAGNETIC-FIELDS

It has been known since the work by Claverie et al. (1982) that integr ated-sunlight velocities measured with the resonance scattering techni que show variations with time scales of weeks to months. The cause can be understood in terms of the effects of solar activity as was pointe d out by Edmunds & Gough (1983) and Andersen & Maltby (1983). The latt er authors included a model calculation based on sunspot areas which s howed good promise of being able to quantitatively reproduce the obser ved velocity shifts. We discuss in this paper a new modeling effort ba sed on daily magnetograms obtained at the 150-ft tower on Mt. Wilson. This type of database is more quantitative than sunspot areas. Similar maps of magnetically sensitive quantities will be measured on a conti nuous time base as part of several planned helioseismology experiments [from space with SOI/MDI on SOHO, see Scherrer et al. (1991) or with ground-based networks, see Hill & Leibacher (1991)]. We discuss the co rrelations between various magnetically sensitive quantities and devel op a new model for the effects of magnetic field on line profiles and surface brightness. From these correlations we integrate the line prof ile changes over the solar surface using observed magnetic field stren gths measured at lambda5250.2. The final output is a new model for the effects of magnetic fields on integrated sunlight velocities which we compare with daily offset velocities derived from the IRIS-T instrume nt at the Observatorio del Teide.