Modelling the longitudinal asymmetry in sunspot emergence: the role of the wilson depression

Watson, F., Fletcher, L., Dalla, S. and Marshall, S. (2009) Modelling the longitudinal asymmetry in sunspot emergence: the role of the wilson depression. Solar Physics, 260(1), pp. 5-19. (doi: 10.1007/s11207-009-9420-z)

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The distributions of sunspot longitude at first appearance and at disappearance display an east-west asymmetry that results from a reduction in visibility as one moves from disk centre to the limb. To first order, this is explicable in terms of simple geometrical foreshortening. However, the centre-to-limb visibility variation is much larger than that predicted by foreshortening. Sunspot visibility is also known to be affected by the Wilson effect: the apparent ‘dish’ shape of the sunspot photosphere caused by the temperature-dependent variation of the geometrical position of the τ = 1 layer. In this article we investigate the role of the Wilson effect on the sunspot appearance distributions, deducing a mean depth for the umbral τ = 1 layer of 500 – 1500 km. This is based on the comparison of observations of sunspot longitude distribution and Monte Carlo simulations of sunspot appearance using different models for spot growth rate, growth time and depth of Wilson depression.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay
Authors: Watson, F., Fletcher, L., Dalla, S., and Marshall, S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Solar Physics
Publisher:Springer Netherlands
ISSN (Online):1573-093X

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
465931Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.Declan DiverScience & Technologies Facilities Council (STFC)ST/F002149/1Physics and Astronomy