On the relationship between the rotational velocity and the field strength of solar magnetic elements

By tracking various solar surface tracers, previous studies have found that magnetic structures, such as plages and sunspots, rotate faster than the quiet solar regions. We investigate how the rotational speed of these magnetic features is related to their magnetic field strength. By use of near-surface horizontal velocities inferred from time-distance helioseismology, we have studied a few Carrington rotations covering the years 1997-2002, from near the solar minimum to the maximum. It is found that the residual rotational velocity of magnetic elements nearly linearly depends on their magnetic field strength: the stronger the magnetic field strength, the faster the magnetic elements rotate relative to the quiet solar regions. It is also found that the magnetic elements rotate faster in the solar maximum years than the elements of the same magnetic strength but in years with moderate solar activity. For all Carrington rotations studied, magnetic elements of the following polarity rotate faster than the leading polarity elements of the same magnetic strength. Possible interpretations of the observed relations are discussed. Prograde supergranular advection may cause the faster rotation of the following polarity elements.