Flares are known to restructure the magnetic field in the corona and to accelerate the gas between the field lines , but their effect on the photosphere is less well studied .
New data of the Solar Optical Telescope ( SOT ) onboard Hinode provide unprecedented opportunity to uncover the photospheric effect of a solar flare , which associates with an active region NOAA AR 10930 on 2006 December 13 .
We find a clear lateral displacement of sunspot penumbral regions scanned by two flare ribbons .
In the impulsive phase of the flare , the flare ribbons scan the sunspot at a speed of around 18 km s ^ { -1 } , derived from Ca II and G-band images .
We find instantaneous horizontal shear of penumbral fibrils , with initial velocities of about 1.6 km s ^ { -1 } , produced when a flare ribbon passes over them .
This velocity decreases rapidly at first , then gradually decays , so that about one hour later , the fibrils return to a new equilibrium .
During the one hour interval , the total displacement of these fibrils is around 2.0 Mm , with an average shear velocity of 0.55 km s ^ { -1 } .
This lateral motion of the penumbral fibrils indicates that the magnetic footpoints of these field lines being rearranged in the corona also move .