  We explore properties and behavior of slow-decaying unipolar sunspot groups
in the framework of the turbulent erosion model suggested by Petrovay and
Moreno-Insertis (1997). The basic concept of the model is the suppression of a
turbulent diffusivity inside a magnetic flux tube by strong magnetic fields. As
a result, the outer turbulent plasma detaches magnetic features primarily from
the external border of a magnetic flux tube. The radius of the tube exhibits
inward progression at a constant rate. The model predicts older sunspots to
decay slower and it seems to be very promising to explain the slow decay of
long-living unipolar sunspot groups. By analyzing the magnetic structure
associated with a sunspot, we did reveal a gradual decrease of the magnetic
structure radius at a constant rate implying the validity of the model.
However, in some cases the derived velocity of the radius decrease was too low:
our calculations provided implausibly high estimations for the lifetime and
maximal area of such sunspots. We discuss possible additional mechanisms
affecting the decay rate of such peculiar sunspots.
