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The solar active region NOAA 11719 produced a large two-ribbon flare on 11April 2013. We have investigated the sudden variations in the photosphericmagnetic fields in this active region during the flare employing themagnetograms obtained in the spectral line Fe I 6173 Angstrom by theHelioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory(SDO). The analysis of the line-of-sight magnetograms from HMI show sudden andpersistent magnetic field changes at different locations of the active regionbefore the onset of the flare and during the flare. The vector magnetic fieldobservations available from HMI also show coincident variations in the totalmagnetic field strength and its inclination angle at these locations. Using thesimultaneous Dopplergrams obtained from HMI, we observe perturbations in thephotospheric Doppler signals following the sudden changes in the magneticfields in the aforementioned locations. The power spectrum analysis of thesevelocity signals show enhanced acoustic power in these affected locationsduring the flare as compared to the pre-flare condition. Accompanying theseobservations, we have also used the near-simultaneous chromosphericobservations obtained in the spectral line H-alpha 6562.8 Angstrom by theGlobal Oscillation Network Group (GONG) to study the evolution of flare ribbonsand intensity oscillations in the active region. The H-alpha intensityoscillations also show enhanced oscillatory power during the flare in theaforementioned locations. These results indicate that the transient Lorentzforce associated with the sudden changes in the magnetic fields could drive thelocalized photospheric and chromospheric oscillations, like the flare-inducedoscillations in the solar atmosphere.

Analysis of sudden variations in photospheric magnetic fields during a large flare and their influences in the solar atmosphere