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R. F. Howard (National Solar Observatory)
The Sun presents us with an array of velocity fields, probably the most obvious of which is granulation. A larger convective pattern known as "supergranulation" is also clearly seen in the chromosphere. There is indirect evidence for still larger organized motions within the convective zone. This evidence comes from the effects of these motions on the orientation and behavior of active regions at the solar surface. As loops of magnetic flux rise through the convective zone to emerge eventually as active regions, they are acted upon by several forces, such as the Coriolis force, and this results in the orientations and motions of the regions observed at the solar surface. Differential rotation is yet another large-scale velocity pattern that is of importance for understanding the structure and the activity cycle of the Sun - and of solar-type stars. Small systematic variations in the differential rotation are linked in space and time with the well-known latitude drift of activity (i.e. sunspot groups) during a 22-year cycle. This phenomenon is clearly related to the dynamo process that is the cause of the solar cycle of activity.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.