Differential Rotation Derived from Individual Sunspot Measurements

Base on 484 individual sunspot proper motion measurements during the period 1989 to 1995, we made a study of solar differential rotation. The linear drift method from the observed individual sunspot was used. The formula of differential rotation as a function of solar latitude, B can be written as ω(B) = a + b sin² B, where a=14.5± 0.5 ^o/d and b=-2.4 ± 0.4 ^o/d. The separation drift of different polarity sunspots was about 72 m/s. By the same linear drift method, daily sunspot group data during the period 1874 to 2000 gave coefficients a=14.501 ± 0.001 ^o/d and b=-2.43 ± 0.08 ^o/d.