Sunspots

Abstract

Some examples of research on structure and formation of sunspots are briefly recollected in historical sequence. They relate to many facets of sunspots, first: magnetic inhibition of convection, the conjecture of a fiat penumbra, the stratification beneath the umbra, the observable magnetic profile, the Evershed effect as syphon flow, the concept of a magnetopause; next: cooling by Alfven waves, evolution and stability, the “bright ring”, the observed change of umbra brightness with the phase of the sunspot cycle, the hypothetical cluster of separate flux strands underneath the umbra, the profile of the magnetopause, the structure of the penumbra and the inclination of its field and finally: the concept of a deep penumbra with volume currents, exchange convection and the concept of a second current sheet separating umbra and penumbra.

Of course, the rigorous theoretical modeling of local magnetoconvection is an essential tool for our understanding of all these processes. I do not deal with it here, but the reader has a fascinating review of magnetoconvection already in his hands (Weiss, 1991).