Large-scale horizontal flows in the solar photosphere

V. Possible evidence for the disconnection of bipolar sunspot groups from their magnetic roots

¹ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191, Katlenburg-Lindau, Germany e-mail: svanda@mps.mpg.de
² Astronomical Institute, Academy of Sciences of the Czech Republic (v. v. i.), Fričova 298, 25165, Ondřejov, Czech Republic e-mail: [mklvana;msobotka]@asu.cas.cz
³ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, Prague, 18200, Czech Republic

Received: 4 May 2009
Accepted: 10 August 2009

Abstract

In a recent paper (Švanda et al. 2008, A&A, 477, 285) we pointed out that, based on the tracking of Doppler features in the full-disc MDI Dopplergrams, the active regions display two dynamically different regimes. We speculated that this could be a manifestation of the sudden change in the active regions dynamics, caused by the dynamic disconnection of sunspots from their magnetic roots as proposed by Schüssler & Rempel (2005, A&A, 441, 337). Here we investigate the dynamic behaviour of the active regions recorded in the high-cadence MDI data over the last solar cycle in order to confirm the predictions in the Schüssler's & Rempel's paper. We find that, after drastic reduction of the sample, which is done to avoid disturbing effects, a large fraction of active regions displays a sudden decrease in the rotation speed, which is compatible with the mechanism of the dynamic disconnection of sunspots from their parental magnetic structures.