Re-examining sunspot tilt angle to include anti-Hale statistics

McClintock, B. H. and Norton, A. A. and Li, J. (2014) Re-examining sunspot tilt angle to include anti-Hale statistics. The Astrophysical Journal, 797 (2). pp. 1-10. ISSN 0004-637X

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Abstract

Sunspot groups and bipolar magnetic regions (BMRs) serve as an observational diagnostic of the solar cycle. We use Debrecen Photohelographic Data (DPD) from 1974-2014 that determined sunspot tilt angles from daily white light observations, and data provided by Li & Ulrich that determined sunspot magnetic tilt angle using Mount Wilson magnetograms from 1974-2012. The magnetograms allowed for BMR tilt angles that were anti-Hale in configuration, so tilt values ranged from 0 to 360° rather than the more common ±90°. We explore the visual representation of magnetic tilt angles on a traditional butterfly diagram by plotting the mean area-weighted latitude of umbral activity in each bipolar sunspot group, including tilt information. The large scatter of tilt angles over the course of a single cycle and hemisphere prevents Joy's law from being visually identified in the tilt-butterfly diagram without further binning. The average latitude of anti-Hale regions does not differ from the average latitude of all regions in both hemispheres. The distribution of anti-Hale sunspot tilt angles are broadly distributed between 0 and 360° with a weak preference for east-west alignment 180° from their expected Joy's law angle. The anti-Hale sunspots display a log-normal size distribution similar to that of all sunspots, indicating no preferred size for anti-Hale sunspots. We report that 8.4% ± 0.8% of all bipolar sunspot regions are misclassified as Hale in traditional catalogs. This percentage is slightly higher for groups within 5° of the equator due to the misalignment of the magnetic and heliographic equators.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version made accessible, in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 21 Feb 2015 00:01
Last Modified: 24 Mar 2017 02:55
Uncontrolled Keywords: sunspots
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020109 Space and Solar Physics
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020107 Mesospheric, Ionospheric and Magnetospheric Physics
01 Mathematical Sciences > 0105 Mathematical Physics > 010505 Mathematical Aspects of Quantum and Conformal Field Theory, Quantum Gravity and String Theory
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1088/0004-637X/797/2/130
URI: http://eprints.usq.edu.au/id/eprint/26516

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