MAKING SENSE OF SUNSPOT DECAY - I - PARABOLIC DECAY LAW AND GNEVYSHEV-WALDMEIER RELATION

In a statistical study of the decay of individual sunspots based on DP R data we find that the mean instantaneous area decay rate is related to the spot radius r(0) and the maximum radius r(0) as D = C(D)r/r(0), C-D = 32.0 +/- 0.26 MSH day(-1). This implies that sunspots on the me an follow a parabolic decay law; the traditional linear decay law is e xcluded by the data. The validity of the Gnevyshev-Waldmeier relations hip between the maximum area A(0) and lifetime T of a spot group, A(0) /T similar or equal to 10 MSH day(-1), is also demonstrated for indivi dual sunspots. No evidence is found for a supposed supergranular 'quan tization' of sunspot areas. Our results strongly support the recent tu rbulent erosion model of sunspot decay while all other models are excl uded.