Left panel: simultaneous observations of the magnetic field variations (maximum values) in two sunspots: NOAA 11232 (S1) and NOAA 11228 (S2). The active regions field-of-view is [100″ × 100″]. The S1 center coordinates are [− 552″ × 168″], and the S2 coordinates are [110″ × 297″] obtained at 20:00 UT on 2011 Jun. 04. The time series starts at 00:00 UT on 2011 Jun. 04. Right panel: detrended and superposed time series. The magnetic field B is the value of the magnetic field strength avareged over the small area near the point of the maximum magnitude inside the umbra. As a rule, this point does not coincide with the geometrical center of the umbra.