Spatial Spectra of Magnetic Fields and Current Helicity by Using Hinode/SOT-SP Mosaic Magnetograms

Helical nature of magnetic fields represented by indices like current helicity gives crucial hints on the generation mechanism (dynamo mechanism) of solar magnetic fields. We have already published such a study (Otsuji et al., PASJ 2015) using the data from Hinode/SOT-SP. The advantage of high spatial resolution provided by Hinode/SOT was clearly demonstrated, while generally its field of view marginally covered large active regions. We found some indications that contributions to current helicity may have different signs from structures with large and small scales. In order to study properties of helicity in scales of active regions more in detail, we have proposed and carried out SOT-SP multiple raster scans to build up "overlapping mosaic maps" with a larger effective field of view. In the period between 2014 and 2017 we obtained 11 such successful scans. We derived power spectra of magnetic field components and current helicity, and found that contributions to current helicity generally change sign as a function of wavenumber. How this property is linked to the so-called hemispheric sign rule of helicity is still not clear because of small sample size of mosaic observations.