HAO Colloquium - On the (in)stability of sunspots

Speaker: Hanna Strecker, Instituto de AstrofĂ­sica de AndalucĂ­a

The (in)stability of sunspots is one of the unresolved questions in the field of solar magnetism. Effects such as fluting instability and buoyancy forces acting below the solar surface and affecting sunspot stability can currently only be studied in numerical simulations. I will present our study on (de)stabilising effects on the flux tube of a simulated sunspot in the upper convection zone. This analysis is enabled by a simulation domain with a horizontal dimension of 98 Mm x 98 Mm and a vertical extension of 18 Mm. We investigate the evolution of the flux tube at selected depths using two methods: (1) the relative change in the ratio between perimeter and area of the flux tube and (2) the application of a linear stability analysis. We find a depth dependent corrugation of the flux tube along its perimeter. This is strongest below the visible solar surface. Intrusions of field-free plasma form at the boundary of the flux tube. Buoyancy forces stabilise the flux tube against interchange instability towards the surface, where the sunspot appears to be stable. Below the visible surface, interchange instability destabilises the flux tube and might cause the onset of sunspot decay.

Date and time: 
Wednesday, December 8, 2021 - 2:00pm to 3:00pm