Sunspot Simulations: Penumbra Formation and the Fluting Instability

Thick penumbra in a magnetostatic sunspot model

The conjecture that energy transport in sunspot penumbrae occurs through convection by an interchange of magnetic flux tubes is used in order to construct a magnetostatic model for a deep penumbra which is part of a global sunspot model. The model describes an overall mechanical equilibrium between the three stratifications: of the umbra, the penumbra, and of the solar convection zone, all of t...

Structure of proper motions in a sunspot penumbra

Small-scale flow field in a sunspot penumbra

We have measured velocity maps of a round sunspot near the center of the solar disk. We derive the small-scale velocity field of the penumbra in the deep photosphere. Superimposed on a radial outflow, we find up– and downflows, which are associated with bright and dark features: The flow in the dark component of the penumbra has a larger inclination angle with respect to the surface normal than...

Evolution of a Magnetic Flux Tube in a Sunspot Penumbra

The motion of an individual magnetic flux tube inside the penumbra of a sunspot is studied numerically. Here, we present preliminary results. The thin flux tube approximation together with a simplified radiative heat exchange with the surroundings is used to study the evolution of a flux tube embedded into a background given by a global magneto-static sunspot model. The investigation is underta...

High-resolution spectro-polarimetry of a flaring sunspot penumbra

We present simultaneous photospheric and chromospheric observations of the trailing sunspot in NOAA 10904 during a weak flare eruption (GOES magnitude B7.8), obtained with the Swedish Solar Telescope (SST) in La Palma, Canary Islands. High-resolution Ca iiH images show a typical two-ribbon structure that has been hitherto only known for larger flares, and the flare appears in a confined region ...