Variations in the longitudinal magnetic field in NOAA 11476 and NOAA 11515 during M-class solar flares are studied. Magnetic field observations were made by the Solar Dynamics Observatory using the Helioseismic and Magnetic Imager (SDO/HMI) with temporal and spatial resolutions of 45 s and 0".5 pixel-1, respectively. During the maximum phase of the M5.7/2B flare of May 9, 2012, in NOAA 11476, and the M5.3/2B flare of July 4, 2012, in NOAA 11515, there were abrupt changes in the magnetic field of the active regions. Transient structures with the opposite sign appeared in high magnetic fields with negative polarity. The transients were located in the umbra of sunspots and lasted several minutes. We study these features of the magnetic field in detail.
sun activity flares magnetic field
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