Choudhuri, A. R. (1986) The dynamics of magnetically trapped fluids. I. Implications for umbral dots and penumbral grains The Astrophysical Journal, 302 . pp. 809-825. ISSN 0004-637X
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Official URL: http://adsabs.harvard.edu/abs/1986ApJ...302..809C
Related URL: http://dx.doi.org/10.1086/164042
Abstract
A study of the magnetohydrodynamic system in which a nonmagnetized fluid in a gravitational field is surrounded by a fluid carrying a vertical magnetic field is presented. It is pointed out that this study can throw some light on the fine-structural features of a sunspot. The equilibrium configuration of the field-free fluid is a tapering column ending at an apex. The regions away form the apex can be studied by the slender flux tube approximation. A scheme developed to treat the apex indicates that, just below the apex, the radius of the tapering column opens up with a 3/2 power dependence on the depth below the apex. If the internal pressure of the field-free fluid is increased, the apex rises, and a static equilibrium may not be possible beyond a limit if the magnetic pressure drops quickly above a certain height. The nature of steady-flow solutions beyond this limit is investigated. Under conditions inside a sunspot, a column of field-free gas is found to rise with a velocity of about 100 km/hr. If umbral dots and penumbral grains are interpreted as regions where the field-free gas ultimately emerges, a very natural explanation of most of their observed properties is obtained.
Item Type: | Article |
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Source: | Copyright of this article belongs to The American Astronomical Society. |
Keywords: | Magnetohydrodynamics; Solar Granulation; Solar Magnetic Field; Sunspots; Fluid Pressure; Incompressible Fluids; Magnetic Flux; Polytropic Processes; Steady Flow |
ID Code: | 66558 |
Deposited On: | 24 Oct 2011 08:18 |
Last Modified: | 18 May 2016 14:03 |
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