Stokes Profile Asymmetries in Solar Active Regions

Abstract

Asymmetries in Stokes polarization spectral line proÐles can be attributed to the existence of gradients in the velocity (and magnetic Ðeld) over the line-forming region. Models that solve the Stokes radiative transfer equations have incorporated both line-of-sight gradients and gradients perpendicular to the line of sight over the resolution element to produce the observed asymmetries. There have been only a few systematic studies of how these Stokes proÐle asymmetries vary across spatial structures and as a function of the amplitude of the velocity and magnetic Ðelds, and very little statistical information is available. We present observational results from high spectral and spatial resolution Stokes V proÐle measurements made in an active region located near disk center and present correlations between the amplitude of the Stokes V asymmetry, the magnetic Ðeld strength, and line shifts and line asymmetries observed in the Stokes I proÐle. In regions where the Ðeld strength exceeds a few hundred gauss, we Ðnd a good correlation between the amplitude of the measured asymmetry in Stokes V and the observed shifts of the Stokes I proÐle. We also Ðnd a correlation between the asymmetry of the Stokes I proÐle and the amplitude of the Stokes V proÐle asymmetry.