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A new look at sunspot formation using theory and observations

Published online by Cambridge University Press:  12 September 2017

I. R. Losada ,
J. Warnecke ,
K. Glogowski ,
M. Roth ,
A. Brandenburg ,
N. Kleeorin  and
I. Rogachevskii
I. R. Losada
Affiliation:
Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden, email: illa.rivero.losada@gmail.com Department of Astronomy, Stockholm University, SE-10691 Stockholm, Sweden Nordic Optical Telescope, Apartado 474, E-38700 Santa Cruz de La Palma, Spain Kiepenheuer-Institut für Sonnenphysik, Schöneckstraße 6, D-79104, Freiburg, Germany
J. Warnecke
Affiliation:
Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
K. Glogowski
Affiliation:
Kiepenheuer-Institut für Sonnenphysik, Schöneckstraße 6, D-79104, Freiburg, Germany
M. Roth
Affiliation:
Kiepenheuer-Institut für Sonnenphysik, Schöneckstraße 6, D-79104, Freiburg, Germany
A. Brandenburg
Affiliation:
Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden, email: illa.rivero.losada@gmail.com Department of Astronomy, Stockholm University, SE-10691 Stockholm, Sweden Laboratory for Atmospheric and Space Physics, JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80303, USA
N. Kleeorin
Affiliation:
Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden, email: illa.rivero.losada@gmail.com Department of Mechanical Engineering, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel
I. Rogachevskii
Affiliation:
Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden, email: illa.rivero.losada@gmail.com Department of Mechanical Engineering, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 84105, Israel
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Abstract

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Sunspots are of basic interest in the study of the Sun. Their relevance ranges from them being an activity indicator of magnetic fields to being the place where coronal mass ejections and flares erupt. They are therefore also an important ingredient of space weather. Their formation, however, is still an unresolved problem in solar physics. Observations utilize just 2D surface information near the spot, but it is debatable how to infer deep structures and properties from local helioseismology. For a long time, it was believed that flux tubes rising from the bottom of the convection zone are the origin of the bipolar sunspot structure seen on the solar surface. However, this theory has been challenged, in particular recently by new surface observation, helioseismic inversions, and numerical models of convective dynamos. In this article we discuss another theoretical approach to the formation of sunspots: the negative effective magnetic pressure instability. This is a large-scale instability, in which the total (kinetic plus magnetic) turbulent pressure can be suppressed in the presence of a weak large-scale magnetic field, leading to a converging downflow, which eventually concentrates the magnetic field within it. Numerical simulations of forced stratified turbulence have been able to produce strong super-equipartition flux concentrations, similar to sunspots at the solar surface. In this framework, sunspots would only form close to the surface due to the instability constraints on stratification and rotation. Additionally, we present some ideas from local helioseismology, where we plan to use the Hankel analysis to study the pre-emergence phase of a sunspot and to constrain its deep structure and formation mechanism.

Keywords

Sun: sunspotsSun: magnetic fieldsturbulencehelioseismology
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 12 , Symposium S327: Fine Structure and Dynamics of the Solar Atmosphere , October 2016 , pp. 46 - 59
Copyright
Copyright © International Astronomical Union 2017 

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