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Current helicity and twist of solar magnetic fields are important quantitiesto 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 activeregions observed with the Spectro-Polarimeter (SP) of Hinode Solar OpticalTelescope (SOT). We used SOT-SP data of 558 vector magnetograms of a total of80 active regions obtained from 2006 to 2012. We have applied spatial smoothingand division of data points into weak and strong field ranges to compare thecontributions from different scales and field strengths. We found that thecurrent helicity follows the so-called hemispheric sign rule when the weakmagnetic fields (absolute field strength $< 300$ gauss) are considered and nosmoothing is applied. On the other hand, the pattern of current helicityfluctuates and violates the hemispheric sign rule when stronger magnetic fieldsare considered and the smoothing of 2.0 arcsec (mimicking ground-basedobservations) is applied. Furthermore, we found a tendency that the weak andinclined fields better conform to and the strong and vertical fields tend toviolate the hemispheric sign rule. These different properties of helicitythrough the strong and weak magnetic field components give important clues tounderstanding the solar dynamo as well as the mechanism of formation andevolution of solar active regions.

publications of the astronomical society of japan

Statistical Analysis of Current Helicity and Twist in Solar Active  Regions over the Phases of the Solar Cycle Using the Spectro-Polarimeter Data  of Hinode