  Using the 135-second cadence of the photospheric vector data provided by the
Helioseismic and Magnetic Imager telescope on board the Solar Dynamic
Observatory, we examined the time-evolution of magnetic helicity fluxes across
the photosphere during 16 flares with the energy class lower than M5.0. During
the flare in 4 out of 16 events, we found impulsive changes in the helicity
fluxes. This indicates that even the flare with less energy could be associated
with anomalistic transportation of the magnetic helicity across the
photosphere. Accompanying the impulsive helicity fluxes, the poynting fluxes
across the photosphere evolved from positive to negative. As such, the
transportations of magnetic energy across the photosphere were toward solar
interior during these flares. In each of the 4 events, the impulsive change in
the helicity flux was always mainly contributed by abrupt change in horizontal
velocity field on a sunspot located near the flaring polarity inversion line.
The velocity field on each sunspot shows either an obvious vortex patten or an
shearing patten relative to the another magnetic polarity, which tended to
relax the magnetic twist or shear in the corona. During these flares, abrupt
change in the Lorentz force acting on these sunspots were found. The rotational
motions and shearing motions of these sunspots always had the same directions
with the resultant Lorentz forces. These results support the view that the
impulsive helicity transportation during the flare could be driven by the
change in the Lorentz force applied on the photosphere.
