Differential Rotation of Strong Magnetic Flux During Solar Cycles 21 - 23

In the present investigation we measure the differential rotation of strong magnetic flux during solar cycles 21 - 23 with the method of wavelet transforms. We find that the cycle-averaged synodic rotation rate of strong magnetic flux can be written as ω=13.47-2. 58sin ²θ or ω=13.45-2.06sin ²θ-1.37sin ⁴θ, where θ is the latitude. They agree well with the results derived from sunspots. A north-south asymmetry of the rotation rate is found at high latitudes (28°<θ<40°). The strong flux in the southern hemisphere rotates faster than that in the northern hemisphere by 0.2 deg day^-1. The asymmetry continued for cycles 21 - 23 and may be a secular property.