Active region magnetic fields

The tilt angles of sunspot groups are defined, using the Mount Wilson data set. It is shown that groups with tilt angles greater than or less than the average value (approximate to 5 deg) show different latitude dependences. This effect is also seen in synoptic magnetic field data defining plages, T he fraction of the total sunspot group area that is found in the leading sp ots is discussed as a parameter that can be useful in studying the dynamics of sunspot groups. This parameter is larger for low tilt angles, and small for extreme tilt angles in either direction. The daily variations of sunsp ot group tilt angles are discussed. The result that sunspot tilt angles ten d to rotate toward the average value is reviewed. It is suggested that at s ome depth, perhaps 50 Mm, there is a flow relative to the surface that resu lts from a relation rate faster than the surface rate by about 60 m/sec and a meridional dt ift that is slower than the surface rate by about 5 m/sec. This results in a slanted relative flow at that depth that is in the direc tion of the average tilt angle and may be responsible for the tendency for sunspot groups (and plages) to rotate their magnetic axes in the direction of the average tilt angle.