Invisible sunspots and rate of solar magnetic flux emergence

Dalla, S., Fletcher, L. and Walton, N.A. (2008) Invisible sunspots and rate of solar magnetic flux emergence. Astronomy and Astrophysics, 479(1), L1-L4. (doi:10.1051/0004-6361:20078800)

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Publisher's URL: http://dx.doi.org/10.1051/0004-6361:20078800

Abstract

<p><b>Aims:</b> We study the visibility of sunspots and its influence on observed values of sunspot region parameters.</p> <p><b>Methods:</b> We use Virtual Observatory tools provided by AstroGrid to analyse a sample of 6862 sunspot regions. By studying the distributions of locations where sunspots were first and last observed on the solar disk, we derive the visibility function of sunspots, the rate of magnetic flux emergence and the ratio between the durations of growth and decay phases of solar active regions.</p> <p><b>Results:</b> We demonstrate that the visibility of small sunspots has a strong centre-to-limb variation, far larger than would be expected from geometrical (projection) effects. This results in a large number of young spots being invisible: 44% of new regions emerging in the west of the Sun go undetected. For sunspot regions that are detected, large differences exist between actual locations and times of flux emergence, and the apparent ones derived from sunspot data. The duration of the growth phase of solar regions has been, up to now, underestimated.</p>

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay
Authors: Dalla, S., Fletcher, L., and Walton, N.A.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN:0004-6361
ISSN (Online):1432-0746
Copyright Holders:Copyright © 2008 EDP Sciences
First Published:First published in Astronomy and Astrophysics 479(1):L1-L4
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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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