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

Published online by Cambridge University Press:  12 April 2016

K. Petrovay  and
G. Szakály
K. Petrovay
Affiliation:
Eötvös University, Department of Astronomy, Budapest, Ludovika tér 2, H-1083Hungary
G. Szakály
Affiliation:
Eötvös University, Department of Astronomy, Budapest, Ludovika tér 2, H-1083Hungary

Abstract

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The 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.

Type
Session 2. Theory of Active Region Structure
Information
International Astronomical Union Colloquium , Volume 141: The Magnetic and Velocity Fields of Solar Active Regions , 1993 , pp. 108 - 111
Copyright
Copyright © Astronomical Society of the Pacific 1993

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