Polar cap magnetic field reversals during solar grand minima: could pores play a role?

¹ Astronomical Institute (v. v. i.), Czech Academy of Sciences, Fričova 298, 25165 Ondřejov, Czech Republic
e-mail: michal@astronomie.cz
² Astronomical Institute, Charles University in Prague, Faculty of Mathematics and Physics, V Holešovičkách 2, 18000 Prague 8, Czech Republic
³ Laboratoire AIM Paris-Saclay, CEA/Irfu Université Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette, France
⁴ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, 14 avenue Édouard Belin, 31400 Toulouse, France

Received: 5 September 2015
Accepted: 21 November 2015

Abstract

We study the magnetic flux carried by pores located outside active regions with sunspots and investigate their possible contribution to the reversal of the global magnetic field of the Sun. We find that they contain a total flux of comparable amplitude to the total magnetic flux contained in polar caps. The pores located at distances of 40–100 Mm from the closest active region systematically have the correct polarity of the magnetic field to contribute to the polar cap reversal. These pores can be found predominantly in bipolar magnetic regions. We propose that during grand minima of solar activity, such a systematic polarity trend, which is akin to a weak magnetic (Babcock-Leighton-like) source term, could still be operating but was missed by the contemporary observers because of the limited resolving power of their telescopes.