A new dynamo pattern revealed by the tilt angle of bipolar sunspot groups

Abstract

We obtain the latitude-time distribution of the averaged tilt angle of solar bipoles. for large bipoles, which are mainly bipolar sunspot groups, the spatially averaged tilt angle is positive in the northern solar hemisphere and negative in the southern, with modest variations during the course of the solar cycle. we consider the averaged tilt angle to be a tracer for a crucial element of the solar dynamo, i.e. the regeneration rate of poloidal large-scale magnetic field from toroidal. the value of the tilt obtained crudely corresponds to a regeneration factor corresponding to about 10 per cent of rms velocity of solar convection. these results develop findings of stenflo & kosovichev concerning joy's law, and agree with the usual expectations of solar dynamo theory. quite surprisingly, we find a pronounced deviation from these properties for smaller bipoles, which are mainly solar ephemeral regions. they possess tilt angles of approximately the same absolute value, but of opposite sign compared to that of the large bipoles. of course, the tilt data for small bipoles are less well determined than those for large bipoles; however, they remain robust under various modifications of the data processing. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.