Estimation of the depths of initial anchoring and the rising-rates of sunspot magnetic structures from rotation frequencies of sunspot groups

Abstract

The mean variation of the `initial' rotation frequency of sunspot groups, with the life span of spot groups in the range 12 to 2 days, has its trend similar to the radial variation of plasma rotation frequency, {OMEGA}(r), across the convective envelope at 15° latitude as given by helioseismology. The mean variation, with age, of the rotation frequency of sunspot groups which live for 10-12 days in latitudes 10°-20° also has its trend similar to {OMEGA}(r). These results suggest: (i) In all latitudes, the magnetic structures (e.g, bunch of flux tubes) of spot groups which live for 2 days are initially anchored near the surface (radial distance r~650Mm), and those of spot groups which live successively longer are initially anchored in successively deeper layers, by ~21000km per day, (ii) the structures which yield spot groups living 10-12 days are initially anchored near the base of the convective envelope. For a spot group which lives 10-12 days in latitudes 10°-20°, the `anchoring layer' of its magnetic structure rises at a rate ~21000km/day, as the spot group ages.