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Solar Physics

, Volume 289, Issue 4, pp 1143–1152 | Cite as

Bimodal Distribution of Magnetic Fields and Areas of Sunspots

  • Andrey G. Tlatov
  • Alexei A. PevtsovEmail author
Article

Abstract

We applied automatic identification of sunspot umbrae and penumbrae to daily observations from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to study their magnetic flux density (B) and area (A). The results confirm an already known logarithmic relationship between the area of sunspots and their maximum flux density. In addition, we find that the relation between average magnetic flux density (\(B_{\rm avg}\)) and sunspot area shows a bimodal distribution: for small sunspots and pores (A≤20 millionth of solar hemisphere, MSH), \(B_{\rm avg} \approx 800~\mbox{G}\) (gauss), and for large sunspots (A≥100 MSH), \(B_{\rm avg}\) is about 600 G. For intermediate sunspots, average flux density linearly decreases from about 800 G to 600 G. A similar bimodal distribution was found in several other integral parameters of sunspots. We show that this bimodality can be related to different stages of sunspot penumbra formation and can be explained by the difference in average inclination of magnetic fields at the periphery of small and large sunspots.

Keywords

Sun: surface magnetism Sunspots Sun: activity 

Notes

Acknowledgements

A.G.T. acknowledges support by the Russian Foundation for Basic Research (RFBR) and the Russian Academy of Sciences (RAS). The National Solar Observatory is operated by the Association of Universities for Research in Astronomy (AURA), Inc. under a cooperative agreement with the National Science Foundation.

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Kislovodsk Solar Station of Pulkovo ObservatoryKislovodskRussian Federation
  2. 2.National Solar ObservatorySunspotUSA

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