  Current helicity and twist of solar magnetic fields are important quantities
to characterize the dynamo mechanism working in the convection zone of the Sun.
We have carried out a statistical study on the current helicity of solar active
regions observed with the Spectro-Polarimeter (SP) of Hinode Solar Optical
Telescope (SOT). We used SOT-SP data of 558 vector magnetograms of a total of
80 active regions obtained from 2006 to 2012. We have applied spatial smoothing
and division of data points into weak and strong field ranges to compare the
contributions from different scales and field strengths. We found that the
current helicity follows the so-called hemispheric sign rule when the weak
magnetic fields (absolute field strength $< 300$ gauss) are considered and no
smoothing is applied. On the other hand, the pattern of current helicity
fluctuates and violates the hemispheric sign rule when stronger magnetic fields
are considered and the smoothing of 2.0 arcsec (mimicking ground-based
observations) is applied. Furthermore, we found a tendency that the weak and
inclined fields better conform to and the strong and vertical fields tend to
violate the hemispheric sign rule. These different properties of helicity
through the strong and weak magnetic field components give important clues to
understanding the solar dynamo as well as the mechanism of formation and
evolution of solar active regions.
