Active region magnetic fields |
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| Authors: | Robert F Howard |
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| Institution: | (1) National Solar Observatory, 85726 Tucson, Arizona, USA |
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| Abstract: | 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 (≈ 5 deg) show different latitude dependences. This effect is also seen in
synoptic magnetic field data defining plages. The fraction of the total sunspot group area that is found in the leading spots
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 sunspot group tilt angles are
discussed. The result that sunspot tilt angles tend to rotate toward the average value is reviewed. It is suggested that at
some depth, perhaps 50 Mm, there is a flow relative to the surface that results from a rotation rate faster than the surface
rate by about 60 m/sec and a meridional drift 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 direction 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. |
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| Keywords: | Active regions sunspot groups group tilt angles |
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