In this paper, we investigate impulsive variations of the magnetic helicity change rate associated with eruptive solar flares (three X class flares and one M class flare) accompanying halo coronal mass ejections. By analyzing four sets of 1 minute cadence full-disk magnetograms taken by the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, we have determined the rates of magnetic helicity transport due to horizontal photospheric motions. We have found that magnetic helicity of the order of 1041 Mx2 was impulsively injected into the corona around the flaring peak time of all the flares. We also found that there is a positive correlation between the impulsively injected magnetic helicity and the X-ray peak flux of the associated flare. The impulsive helicity variations are attributed to horizontal velocity kernels localized near the polarity inversion lines. Finally, we report that there is a close spatial proximity between the horizontal velocity kernels and Hα bright points.
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