NOAA11823 as seen in continuum (left panels) and line-of-sight magnetic field strength (right panels) on August 21st 2013 at 15:00:45 UTC as observed by HMI (a)+c)+d)) and ROSA b). The black squares mark the analyzed region. The insets (b)+d)) show the sunspot with contours indicating the inner and outer penumbral boundary from the time-averaged HMI continuum intensity. The HMI magnetogram is scaled from −1 kG (black) to 2 kG (white).