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

Norton, A. A. and Jones, E. H. and Liu, Y. (2013) How do the magnetic field strengths and intensities of sunspots vary over the solar cycle? In: Eclipse on the Coral Sea: Cycle 24 Ascending, 12-16 Nov 2012, Palm Cove, Australia.

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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.


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Item Type: Conference or Workshop Item (Commonwealth Reporting Category E) (Paper)
Refereed: Yes
Item Status: Live Archive
Additional Information: © 2013 Published under licence by IOP Publishing Ltd. Open access journal.
Faculty / Department / School: Current - USQ Other
Date Deposited: 29 Jul 2013 01:36
Last Modified: 14 Sep 2014 23:52
Uncontrolled Keywords: sunspots; rising phase; umbrae; brightness; Carrington rotations
Fields of Research : 04 Earth Sciences > 0401 Atmospheric Sciences > 040102 Atmospheric Dynamics
02 Physical Sciences > 0204 Condensed Matter Physics > 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020109 Space and Solar Physics
Socio-Economic Objective: D Environment > 96 Environment > 9602 Atmosphere and Weather > 960202 Atmospheric Processes and Dynamics
Identification Number or DOI: 10.1088/1742-6596/440/1/012038
URI: http://eprints.usq.edu.au/id/eprint/23806

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