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Sunspots and the physics of magnetic flux tubes. IX - Umbral dots and longitudinal overstabilityThe dynamical properties of the sunspot field and of a column of hot gas confined by such a vertical magnetic field are examined in order to understand the umbral dot within the context of the magnetic sunspot structure. Attention is given to the conditions necessary for gas intrusion, longitudinal as well as convective overstability, the growing modes, and the even mode. With the hypothesis that the subsurface magnetic field of a sunspot splits into many separate flux tubes with field-free gas between, it is suggested that the field-free columns occasionally punch their way up through the overlying magnetic field to the surface, appearing there as the bright, field-free umbral dots. Effects fostering the phenomenon are also discussed, that is, the enhanced temperature of a column of rising gas, the strongly reduced overhead magnetic pressure, and the initiated upward intrusion; these effects are illustrated with examples.
Document ID
19800054266
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Parker, E. N.
(Chicago, University Chicago, Ill., United States)
Date Acquired
August 10, 2013
Publication Date
November 15, 1979
Publication Information
Publication: Astrophysical Journal
Subject Category
Solar Physics
Accession Number
80A38436
Funding Number(s)
CONTRACT_GRANT: NGL-14-001-001
Distribution Limits
Public
Copyright
Other

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