Contributed Talk - Splinter HiRes
Wednesday, 20 September 2017, 17:45 (Auditorium MPS)
The Jur\vcák criterion: Magnetic property of boundaries in pores, proto-spots, and umbrae
Markus Schmassmann, Philip Lindner, Michael Pircher, Nazaret Bello González, Morten Franz,
& Rolf Schlichenmaier
Kiepenheuer-Institut für Sonnenphysik, Freiburg
The various ways of energy transport in radiatively driven magneto-convection determine the structure of sunspots. At first glance, sunspots are composed of a dark umbra and a brighter penumbra. The transition between umbral and penumbral has only recently been discovered to depend on an invariant magnetic property: a value of 1860 G for the vertical magnetic field component. This Jur\vcák criterion states that region with values smaller than that value are prone to form a penumbra, and that fully-fledged stable sunspots have their umbral-penumbral boundary at that value. We use HMI@SDO and GRIS@GREGOR spectro-polarimetric data to further investigate the boundaries of pores, proto-spots, and umbrae in order to elaborate on the consequences of the Jur\vcák criterion for the stability of these magnetic manifestions.