VECTOR MAGNETIC-FIELD MEASUREMENTS AND PENUMBRAL STRUCTURE

The alignment of penumbral fibrils along the direction of the transverse magnetic field is good in the center of the solar disk, but deteriorates near the limb. This effect was studied on the basis of 15 vector magnetograms from various observatories in the period 1966-1984 for 5 sunspot groups. The results can be described with a simple geometrical model, where the magnetic field vectors and the penumbral fibrils lie in the same vertical plane, the inclination of the penumbra to the solar surface is 0-5-degrees, and the elevation angle of the magnetic field vector is 40-50-degrees. An adequate fit to observations was achieved only when an assumed uncertainty with 25-degrees r.m.s. standard error was introduced in the angle measurements. The results are similar to earlier measurements for the chromosphere, although in the chromosphere the alignment of structures along the transverse magnetic field is better.