The Green Line Corona and Its Relation to the Photospheric Magnetic Field

Abstract

Images of the green Line corona made with the LASCO Cl coronagraph on SOHO are analyzed by applying current-free extrapolations to the observed photospheric field. The Fe VIV lambda 5303 emission is Shown to be closely related to the underlying photospheric field strength. By modeling the observed intensity patterns as a function of latitude and height above the solar limb, we derive an approximate scaling law of the form n(foot) proportional to [B-foot](0.9), where n(foot) is the density of the green line-emitting plasma and [B-foot] is the average field strength at the footprints of the coronal loop. The observed high-latitude enhancements in the green line corona are attributed to the poleward concentration of the large-scale photospheric field. The strongest such enhancements occur where the high-latitude unipolar fields become reconnected to active region flux at lower latitudes; the global emission pattern rotates quasi-rigidly at the rate of the dominant active region complex. The validity of the current-free approximation is assessed by comparing the topology of the observed and simulated green line structures.