3.3 Penumbral modeling
The previous section stresses the point that the penumbra is a phenomenon of complex interaction of
magneto-convective forces and radiation in a regime of inclined magnetic field of intermediate strength. One
simplified view on this problem is to consider a separation between convective plumes and a magnetic
configuration as it is done in the field-free gap model. Another simplified view is by dealing with the
problem in ideal MHD, in which the thin flux tube approximation is applicable. The latter perspective is
taken in the siphon flow model and the dynamic extension of it, the moving tube model. Yet, for a full
understanding it seems necessary to take into account dissipative magneto-convection driven by radiation.
But we want to stress that simplified models often help to isolate the dominating physical processes, and to
understand the essentials.