SOME FACTORS AFFECTING THE GROWTH AND DECAY OF PLAGES

The Mount Wilson coarse array magnetograph data set is analyzed to exa mine the dependence of growth and decay rates on the tilt angles of th e magnetic axes of the regions. It is found that there is a relationsh ip between these quantities which is similar to that found earlier for sunspot groups. Regions near the average tilt angle show larger avera ge (absolute) growth and decay rates. The percentage growth and decay rates show minima (in absolute values) at the average tilt angles beca use the average areas of regions are largest near this angle. This res ult is similar to that derived earlier for sunspot groups. As in the c ase of spot groups, this suggests that, for decay, the effect results from the fact that the average tilt angle may represent the simplest s ubsurface configuration of the flux loop or loops that make up the reg ion. In the case of region growth, it was suggested that the more comp licated loop configuration should result in increased magnetic tension in the flux loop, and thus in a slower ascent of the loop to the surf ace, and thus a slower growth rate. In order to examine this further, the growth and decay rates of plage regions were examined as functions of the magnetic complexity of the regions. In the case of decay, the result was as expected from the model suggested above - that is, the m ore complex regions decayed more slowly. But for growing regions the e ffect is the opposite to that expected (more complex regions grow fast er, even in terms of percentage growth), so the explanation of the til t angle effect for growing regions proposed earlier may not be valid.