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Classification of Magnetoatmospheric Modes in Sunspot Umbrae

Published online by Cambridge University Press:  08 February 2017

S.S. Hasan  and
Y. Sobouti
S.S. Hasan
Affiliation:
Indian Institute of Astrophysics Bangalore 560034, India
Y. Sobouti
Affiliation:
Physics Department Shiraz, Iran

Abstract

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We examine the wave modes in a sunspot umbra. Assuming a stratification, based on a model atmosphere in a sunspot, the normal mode spectrum is determined. The modes are classified using a scheme based on a Helmholtz decomposition of the displacements into l(longitudinal) and t(transverse) components. In certain cases these can be related to the usual fast and slow MHD waves. We compute the theoretical eigenfrequencies and note the existence of umbral oscillations with periods in the range 2-3 min, which are interpreted as slow and mixed modes. The frequencies of the Alfvén waves are also calculated. It is suggested that these modes might also have been observed.

Type
IV. Magnetohydrodynamics of the Photosphere
Information
Symposium - International Astronomical Union , Volume 138: Solar Photosphere: Structure, Convection and Magnetic Fields , 1990 , pp. 255 - 258
Copyright
Copyright © Kluwer 1990 

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