How do the magnetic field strengths and intensities of sunspots vary over the solar cycle?

Paper


Norton, A. A., Jones, E. H. and Liu, Y.. 2013. "How do the magnetic field strengths and intensities of sunspots vary over the solar cycle?" Eclipse on the Coral Sea: Cycle 24 Ascending (2013). Palm Cove, Australia 12 - 16 Nov 2012 Bristol, United Kingdom. https://doi.org/10.1088/1742-6596/440/1/012038
Paper/Presentation Title

How do the magnetic field strengths and intensities of sunspots vary over the solar cycle?

Presentation TypePaper
AuthorsNorton, A. A. (Author), Jones, E. H. (Author) and Liu, Y. (Author)
Journal or Proceedings TitleJournal of Physics: Conference Series
Journal Citation440 (1), pp. 1-8
Number of Pages8
Year2013
Place of PublicationBristol, United Kingdom
ISSN1742-6588
1742-6596
Digital Object Identifier (DOI)https://doi.org/10.1088/1742-6596/440/1/012038
Conference/EventEclipse on the Coral Sea: Cycle 24 Ascending (2013)
Event Details
Eclipse on the Coral Sea: Cycle 24 Ascending (2013)
Event Date
12 to end of 16 Nov 2012
Event Location
Palm Cove, Australia
Abstract

Many efforts have been made to determine if sunspot umbrae continuum intensities and magnetic field strengths are different at sunspot maximum than at sunspot minimum. The results are inconsistent, probably due to differences in sample size and analysis methodology. However, five out of six studies reviewed in this paper agree that sunspots are darker and stronger at sunspot maximum than later in the same cycle, i.e. sunspots brighten during the declining phase of the sunspot cycle. The trend during the rising phase is not agreed upon. Better statistics during the rising phase is crucial to determine if umbrae exhibit a cyclical or linear brightness trend over the cycle. We further this work by analyzing the intensities of 179 sunspots observed with the Helioseismic Magnetic Imager (HMI) for the rising phase of Sunspot Cycle 24. We find no significant trend in the brightness of sunspot umbrae in HMI data during Carrington Rotations 2097-2129 in either hemisphere. Future studies should place limits on sunspots included in the data sample, i.e. use only the leading sunspot in a bipolar active region after most of the flux has emerged but prior to sunspot decay, hopefully separating the effects of surface conditions from those of the interior where the magnetic flux is generated.

Keywordssunspots; rising phase; umbrae; brightness; Carrington rotations
ANZSRC Field of Research 2020370105. Atmospheric dynamics
510404. Electronic and magnetic properties of condensed matter; superconductivity
519999. Other physical sciences not elsewhere classified
Public Notes

© 2013 Published under licence by IOP Publishing Ltd. Open access journal.

Byline AffiliationsStanford University, United States
Centre for Astronomy and Atmospheric Research
Institution of OriginUniversity of Southern Queensland
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