Formation of Coronal Holes on the Ashes of Active Regions
Abstract
We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions. We follow the evolution of four bipolar active regions, and measure their total magnetic flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rate. As a consequence, we see a gradual increase in flux imbalance inside dissipating bipolar magnetic field, and later, a formation of a coronal hole at the site of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of decaying active regions, and two coronal holes had developed at the leading polarity field. Using potential field extrapolation we show that the magnetic field lines of these coronal holes were closed on polar coronal hole at the North, which at the time of the events was in imbalance with the polar coronal hole at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from the old solar cycle to a new cycle.
- Publication:
-
American Astronomical Society Meeting Abstracts #216
- Pub Date:
- May 2010
- Bibcode:
- 2010AAS...21640104K