Journal
ASTROPHYSICAL JOURNAL
Volume 758, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/758/2/115
Keywords
magnetic fields; Sun: dynamo; Sun: general; Sun: interior; Sun: rotation; sunspots
Categories
Funding
- NASA [NNX09AB12G, 16165880]
- NSF [AGS-0958779]
- ONR
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [0958779] Funding Source: National Science Foundation
- NASA [121011, NNX09AB12G] Funding Source: Federal RePORTER
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Tilt angles of close to 30,600 sunspots are determined using Mount Wilson daily averaged magnetograms taken from 1974 to 2012, and SOHO/MDI magnetograms taken from 1996 to 2010. Within a cycle, more than 90% of sunspots have a normal polarity alignment along the east-west direction following Hale's law. The median tilts increase with increasing latitude (Joy's law) at a rate of similar to 0 degrees.5 per degree of latitude. Tilt angles of spots appear largely invariant with respect to time at a given latitude, but they decrease by similar to 0 degrees.9 per year on average, a trend that largely reflects Joy's law following the butterfly diagram. We find an asymmetry between the hemispheres in the mean tilt angles. On average, the tilts are greater in the Southern than in the Northern Hemisphere for all latitude zones, and the differences increase with increasing latitude.
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