Skew Angle and Magnetic Helicity in Solar Active Regions
M. Hagino, Y-J. Moon and T. Sakurai
The skew angle and magnetic helicity are important to understand
magnetic structures in solar active regions. In this study, we have
made the first attempt to examine the relationship between the skew
angle and magnetic helicity. For this we select 129 events whose
longitidues are less than 30 degrees. The skew angle is defined as the
angle between the polarity inversion line (PIL) and the coronal loop
direction, which is defined as the soft X-ray coronal loop axis in
Yohkoh/SXT images. The coronal helicity is determined from the
coronal shear angle that is defined as the angle between the coronal
loop axis and the direction from a positive to a negative sunspot.
Photospheric helicities were computed from vector magnetograms of the
Solar Flare Telescope at Mitaka. We confirmed that the coronal and
photospheric helicity shows a positive correlation, supporting
Pevtsove et al.(1997). We found that an active region which has a
small skew angle tends to have a large helicity value. This result
implies that while a strong twist coronal loop is nearly parallel to a
PIL axis, a weak twist coronal loop is perpendicular to a PIL, like a
potential field structure.
Correspondence
Masaaki Hagino(hagino@kasi.re.kr), Institute: Korea Astronomy and Space Science Institute
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