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A High-resolution Study of Magnetic Field Evolution at Coronal Hole Boundary

Published onAug 18, 2020
A High-resolution Study of Magnetic Field Evolution at Coronal Hole Boundary

In this study, we analyze high spatial resolution (0.24 arcsec) magnetograms and high spatial resolution (0.10 arcsec) Hα off-band (±0.8 Å) images taken by the 1.6 m Goode Solar Telescope (GST) to investigate the magnetic properties in association with small-scale ejections in a coronal hole boundary region from a statistical perspective. With one hour of continuous high-resolution observations in excellent seeing, we focus on the magnetic structure and evolution at the coronal hole boundary and track the magnetic features with the Southwest Automatic Magnetic Identification Suite (SWAMIS). The magnetic field at the studied coronal hole boundary is dominated by negative polarity with magnetic flux cancellations observed at edges of the negative unipolar cluster. In the total of 1250 SWAMIS-detected magnetic cancellation events, ~39% are located inside the coronal hole boundary with a total flux cancellation of 5.4×1020 Mx in an area of 130 Mm2, and ~49% are located outside the corona hole with a total canceled flux of 2.1×1020 Mx in an area of 120 Mm2. We find that the magnetic energy released inside the coronal hole is 6 times more than that outside the coronal hole. Magnetic energy released through small-scale flux cancellations is ~9.5% of the total energy release (2.1×1029 erg), to which granulations and fragmentation of unipolar clusters contribute 90%. We also observed a few significant small-scale ejections associated with magnetic cancellations at the coronal hole boundary that have corresponding EUV brightenings.

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