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

Article


McClintock, B. H., Norton, A. A. and Li, J.. 2014. "Re-examining sunspot tilt angle to include anti-Hale statistics." The Astrophysical Journal: an international review of astronomy and astronomical physics. 797 (2), pp. 1-10. https://doi.org/10.1088/0004-637X/797/2/130
Article Title

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

ERA Journal ID1057
Article CategoryArticle
AuthorsMcClintock, B. H. (Author), Norton, A. A. (Author) and Li, J. (Author)
Journal TitleThe Astrophysical Journal: an international review of astronomy and astronomical physics
Journal Citation797 (2), pp. 1-10
Article Number130
Number of Pages10
Year2014
PublisherIOP Publishing
Place of PublicationUnited States
ISSN0004-637X
1538-4357
Digital Object Identifier (DOI)https://doi.org/10.1088/0004-637X/797/2/130
Web Address (URL)https://iopscience.iop.org/article/10.1088/0004-637X/797/2/130
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.

Keywordssunspots
Contains Sensitive ContentDoes not contain sensitive content
ANZSRC Field of Research 2020519999. Other physical sciences not elsewhere classified
510903. Mesospheric, thermospheric, ionospheric and magnetospheric physics
490205. Mathematical aspects of quantum and conformal field theory, quantum gravity and string theory
Public Notes

File reproduced in accordance with the copyright policy of the publisher/author.

Byline AffiliationsSchool of Agricultural, Computational and Environmental Sciences
Stanford University, United States
University of California, United States
Institution of OriginUniversity of Southern Queensland
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