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How much more can sunspots tell us about the solar dynamo?

Published online by Cambridge University Press:  18 July 2013

Aimee A. Norton ,
Eric H. Jones ,
Y. Liu ,
K. Hayashi ,
J. T. Hoeksema  and
Jesper Schou
Aimee A. Norton
Affiliation:
HEPL, Solar Physics, Stanford University, CA 94305USA, email: aanorton@stanford.edu
Eric H. Jones
Affiliation:
Centre for Astronomy, University of Southern Queensland, Toowoomba, QLD, Australia email: eric.jones@jcu.edu.au
Y. Liu
Affiliation:
HEPL, Solar Physics, Stanford University, CA 94305USA, email: aanorton@stanford.edu
K. Hayashi
Affiliation:
HEPL, Solar Physics, Stanford University, CA 94305USA, email: aanorton@stanford.edu
J. T. Hoeksema
Affiliation:
HEPL, Solar Physics, Stanford University, CA 94305USA, email: aanorton@stanford.edu
Jesper Schou
Affiliation:
HEPL, Solar Physics, Stanford University, CA 94305USA, email: aanorton@stanford.edu
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Abstract

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Sunspot observations inspired solar dynamo theory and continue to do so. Simply counting them established the sunspot cycle and its period. Latitudinal distributions introduced the tough constraint that the source of sunspots moves equator-ward as the cycle progresses. Observations of Hale's polarity law mandated hemispheric asymmetry. How much more can sunspots tell us about the solar dynamo? We draw attention to a few outstanding questions raised by inherent sunspot properties. Namely, how to explain sunspot rotation rates, the incoherence of follower spots, the longitudinal spacing of sunspot groups, and brightness trends within a given sunspot cycle. After reviewing the first several topics, we then present new results on the brightness of sunspots in Cycle 24 as observed with the Helioseismic Magnetic Imager (HMI). We compare these results to the sunspot brightness observed in Cycle 23 with the Michelson Doppler Imager (MDI). Next, we compare the minimum intensities of five sunspots simultaneously observed by the Hinode Solar Optical Telescope Spectropolarimeter (SOT-SP) and HMI to verify that the minimum brightness of sunspot umbrae correlates well to the maximum field strength. We then examine 90 and 52 sunspots in the north and south hemisphere, respectively, from 2010 - 2012. Finally, we conclude that the average maximum field strengths of umbra 40 Carrington Rotations into Cycle 24 are 2690 Gauss, virtually indistinguishable from the 2660 Gauss value observed at a similar time in Cycle 23 with MDI.

Keywords

Sunspotsdynamomagnetic fields
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S294: Solar and Astrophysical Dynamos and Magnetic Activity , August 2012 , pp. 25 - 36
Copyright
Copyright © International Astronomical Union 2013 

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