Morphology and evolution of photospheric magnetic field of the active region NOAA 12297. Panel a: HMI LOS magnetogram of active region NOAA 12297 prior to the onset of the M2.7 flare. Two regions are specified in the active region, which are enclosed by the curves marked by ‘A’ and ‘B’. The yellow five-pointed star indicates the LCO. Panels b–d: temporal evolution of magnetic flux within the whole active region and within the regions marked by ‘A’ and ‘B’, respectively. The dotted curved represent the actual values of magnetic fluxes and the solid curves represent the seven-point running averages of the fluxes. Panel e: GOES 1−8 and 0.5−4 Å flux variations.