Skew Angle and Magnetic Helicity in Solar Active Regions

The skew angle and magnetic helicity are important quantities in understanding the magnetic structures in solar active regions. Using Yohkoh/SXT images and vector magnetograms from the Solar Flare Telescope at Mitaka for 106 active regions, we have made the first attempt to examine the relationship between the skew angle and magnetic helicity. The skew angle is defined as the angle between the coronal loop and the line perpendicular to the polarity inversion line. We found that an active region having a large skew angle tends to have a large helicity value. This result implies that while a coronal loop with strong twist is nearly parallel to the axis of the polarity inversion line, a coronal loop with weak twist is perpendicular to the polarity inversion line, like a potential field structure.