The Sizes of Active Regions and Convective Triggering of the Buoyant Loop Instability

Author:

Petrovay K.,Szakály G.

Abstract

AbstractThe sizes of solar active regions were quantitatively studied using Debrecen Heliographic Results 1977 data. The size-total area dependence was also examined. The size of a region was defined as the distance between the area-weighted mean positions of p- and f-polarity subgroups at the time when the total (umbral + penumbral) area of the spot group is at its maximum. Excluding the groups for which this occurred on the invisible hemisphere and other dubious cases, 68 active regions were left in the present one-year sample. Despite the smallness of this sample, the average size of the regions was found to be 58 400 km with a relatively low error of 3000km (though the individual regions show a considerable scatter in size). It is proposed that the toroidal magnetic flux tubes lie in a sufficiently subadiabatic layer to be linearly stable and they are only destabilized by finite-amplitude convective disturbances that lift parts of them into the unstable layers. In such circumstances the typical size will be determined by the horizontal correlation length of the finite disturbances, thereby explaining the observed size.

Publisher

Cambridge University Press (CUP)

Reference11 articles.

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