  The solar active region NOAA 11719 produced a large two-ribbon flare on 11
April 2013. We have investigated the sudden variations in the photospheric
magnetic fields in this active region during the flare employing the
magnetograms obtained in the spectral line Fe I 6173 Angstrom by the
Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory
(SDO). The analysis of the line-of-sight magnetograms from HMI show sudden and
persistent magnetic field changes at different locations of the active region
before the onset of the flare and during the flare. The vector magnetic field
observations available from HMI also show coincident variations in the total
magnetic field strength and its inclination angle at these locations. Using the
simultaneous Dopplergrams obtained from HMI, we observe perturbations in the
photospheric Doppler signals following the sudden changes in the magnetic
fields in the aforementioned locations. The power spectrum analysis of these
velocity signals show enhanced acoustic power in these affected locations
during the flare as compared to the pre-flare condition. Accompanying these
observations, we have also used the near-simultaneous chromospheric
observations obtained in the spectral line H-alpha 6562.8 Angstrom by the
Global Oscillation Network Group (GONG) to study the evolution of flare ribbons
and intensity oscillations in the active region. The H-alpha intensity
oscillations also show enhanced oscillatory power during the flare in the
aforementioned locations. These results indicate that the transient Lorentz
force associated with the sudden changes in the magnetic fields could drive the
localized photospheric and chromospheric oscillations, like the flare-induced
oscillations in the solar atmosphere.
