Formation of Active Regions: Observations and Theory

Active regions can be used as a diagnostic of the sub-photo-spheric activity. In this review I will discuss how the physical conditions in the subsurface layers of the Sun form and modify the three dimensional complex of the active region. Many characteristics of active regions are related to the conditions under which magnetic ux tubes are generated and to their evolution as they rise in the surface. Statistical observations on active region size distribution, rotation and meridian ow, characteristics of growth and decay, reeect regularities of the behavior of the subsurface ux tubes through which the regions are formed. I will present several recent attempts to model the formation of active regions with diverse methods, such as single ux tube evolution inside the convection zone, statistical mechanics of a collection of magnetic ux tubes, and complex system theory (percolation theory and probabilistic competition models).