What is differential rotation?
5.5 Differential rotation Differential rotation of stars plays an important role in the generation of magnetic fields in the convection zone. In the Sun, it is involved in transformation of a weak large-scale poloidal field into a stronger toroidal component. By analogy, stellar activity is most probably also connected to differential rotation. On the Sun the differential rotation is observed in relative motion of sunspots and can be expressed in the form where denotes heliographic latitude, is the rotation rate at the equator, and is the difference in rotation rate between the pole and the equator. A strength of the differential rotation can be quantified by the rotational shear or its reciprocal , which is the time the equatorial regions need to lap the pole, i.e., the lap time. It can also be characterised by the relative differential rotation rate which is expressed as the ratio of the rotational shear to the equatorial velocity For instance, on the Sun with , the lap time is , and
