Features of Slow Sunspot Dissipation

Resumo

According to a model of sunspot dissipation through a thin boundary layer between the sunspot magnetic flux tube and the surrounding medium, the rate of decrease in the sunspot area must slow as the spot size decreases until it reaches a critical threshold at which the linear law of sunspot dissipation gives way to a nonlinear one. This theoretically predicted effect is confirmed with SOHO/MDI data, which have a high spatial and temporal resolution in comparison with ground-based observations. This work confirms the dissipation slowdown effect in small sunspots. It is reported that the nonlinear dissipation phase derived from discrete receiver (charge-coupled device, CCD) data is somewhat flatter and more diffuse than that derived from continuous radiation receiver data (photographic plates).