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)

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

Project Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
46593	1	Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.	Declan Diver	Science & Technologies Facilities Council (STFC)	ST/F002149/1	Physics and Astronomy