A Comprehensive study of Cavities on the Sun: Structure, Formation, and Evolution
Abstract
Coronal cavities are large-scale structures in the Sun's corona that are closely related with the long-term evolution of the magnetic field in the photosphere as well as associated with the energetic solar activity such as prominence eruptions and coronal mass ejections. They are observed as circular or elliptical-shaped relatively low-density dark regions above the solar limb in EUV, X-ray, and white-light coronal images. We used SDO/AIA limb synoptic maps, constructed from annuli above the solar limb, to systematically identify cavities. We observed 429 coronal prominence cavities between May 20, 2010 and Feb 1, 2015. We examined correlations between height, width, and length of the cavities. Based on the fitting of the shape of the cross section, we classified cavities in three types: prolate (38%), oblate (27%) and circular (35%). We found that the cavities of all shapes are common in shorter length while circular and oblate cavities are more common in the longer length. In general, we found that the overall 3-D topology of long stable cavities can be characterized as a long tube with an elliptical cross-section. Next, we investigated the pattern of cavity location and found that cavity systematically drifts towards the pole. We found that cavities form a belt by making a plot using SDO/HMI surface magnetogram similar to classical buttery diagram of sunspots, we call that the cavity belt. Our analysis showed that the cavity belts migrated towards higher latitude with time and the cavity belts disappeared after the polar magnetic field reversal. This result shows that cavity evolution provides new insight into the solar cycle. Moreover, we studied the underlying magnetic field of a circumpolar crown cavity (Mar 21, 2013- Oct 25, 2013) that was observed for several Carrington Rotations. Our results showed that the underlying polarity inversion line of cavities is formed between the trailing part of decayed active regions and the unipolar magnetic field in the pole. The long life of cavities was due to continuous and sustained adding of trailing flux from multiple active regions as their remnants diffused toward the pole.
- Publication:
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AAS/Solar Physics Division Abstracts #47
- Pub Date:
- May 2016
- Bibcode:
- 2016SPD....4710302K