Abstract
Results of observations of the solar limb effect in the non-magnetic lines Fei 512.4, 543.4, and 709.0 nm are presented. The detailed form of the limb-effect curves depends on the line strength. The weakest line, 709.0, shows a relative blueshift with respect to heliocentric angle from disc center to μ = 0.8 (μ = cos(heliocentric angle)). With increasing line strength the relative blueshift disappears and the redshift increases monotonically from the disc center to the limb. The strongest line, 543.4, shows a nearly linear redshift with decreasing μ, indicating little influence from horizontal motions.
Small, but systematic differences are found for all three lines between the line-shift measurements along the north-south and east-west diameters. The latitudinal variation of the limb effect is largest for the lines formed lowest in the atmosphere. The observations of the strongest line suggest the existence of a poleward meridional flow of 20–25 m s−1. Based on the measurements of the weaker lines a latitude variation in the granulation is suggested. One explanation is that the size of the granulation is about 5% larger at high latitudes as compared to the equatorial region.
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Andersen, B.N. Solar limb effect and meridional flows. Sol Phys 114, 207–222 (1987). https://doi.org/10.1007/BF00167341
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DOI: https://doi.org/10.1007/BF00167341