The dynamics of magnetically trapped fluids. I. Implications for umbral dots and penumbral grains

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
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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