Context. Using Greenwich sunspot data for 120 years it was recently observed that activity regions on the Sun’s surface tend to lie along smoothly changing longitude strips 180◦apart from each other. After critique of the original paper, the new arguments were found to substantiate the claim. Aims. In this paper we analyse new arguments in some detail. Methods. To check basic arguments about pe...

A new analysis of the published long-term photometric observations has revealed permanent active-longitude structures in four RS CVn stars: EI Eri, II Peg, σ Gem, and HR 7275. Two active longitudes separated by half of the period are found to dominate on the surface during all available seasons. The positions of the longitudes on three stars (EI Eri, II Peg, HR 7275) are migrating in the orbita...

The global evolutions of f oF2 anomalies were examined for three very intense geomagnetic storms, namely the Halloween events of October–November 2003 (Event X, 29–30 October 2003, Dst −401 nT; Event Y, 20–21 November 2003, Dst −472 nT), and the largest Dst storm (Event Z, 13–14 March 1989, Dst −589 nT). For Event X, troughs (negative storms) were clearly seen for high northern and southern lat...

Surface reconstructions of active close binary stars based on photometric and spectroscopic observations reveal non-uniform starspot distributions, which indicate the existence of preferred spot longitudes (with respect to the companion star). We consider the equilibrium and linear stability of toroidal magnetic flux tubes in close binaries to examine whether tidal effects are capable to initia...