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APPEARANCES AND STATISTICS OF CORONAL CAVITIES DURING THE ASCENDING PHASE OF SOLAR CYCLE 24  

Nishu Karna   Submitted: 2015-09-14 11:09

We present a survey of 429 coronal prominence cavities found between 2010 May and 2015 February using the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly limb synoptic maps. We examined correlations between each cavity's height, width, and length. Our findings showed that around 38% of the cavities were prolate, 27% oblate, and 35% circular in shape. The lengths of the cavities ranged from 0.06 to 2.9 {R}. When a cavity is longer than 1.5 {R}, it has a narrower height range (0.1?0.3 {R}), whereas when the cavity was shorter than 1.5 {R}, it had a wider height range (0.07?0.5 {R}). We find that the overall three-dimensional topology of the long, stable cavities can be characterized as a long tube with an elliptical cross section. We also noted that the circular and oblate cavities are longer in length than the prolate cavities. We also studied the physical mechanisms behind the cavity drift toward the pole and found it to be tied to the meridional flow. Finally, by observing the evolution of the cavity regions using SDO/Helioseismic Magnetic Imager (HMI) surface magnetic field observations, we found that the cavities formed a belt near the polar coronal hole boundary; we call this the cavity belt. Our results showed that the cavity belt migrated toward higher latitude over time and the cavity belt disappeared after the polar magnetic field reversal. This result shows that cavity evolution provides new insight into the solar cycle.

Authors: N. Karna, W. D. Pesnell, and J. Zhang
Projects: SDO-AIA,SDO-HMI

Publication Status: Published (Sep 8, 2015)
Last Modified: 2015-09-14 16:09
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STUDY OF THE 3D GEOMETRIC STRUCTURE AND TEMPERATURE OF A CORONAL CAVITY USING THE LIMB SYNOPTIC MAP METHOD  

Nishu Karna   Submitted: 2015-09-14 11:08

We present the three-dimensional geometric structure and thermal properties of a coronal cavity deduced from limb synoptic maps. The observations are extreme ultraviolet images from the Atmospheric Imager Assembly (AIA) and magnetic images from the Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory. We describe a limb synoptic-map method used to effectively identify and measure cavities from annuli of radiance above the solar limb. We find that cavities are best seen in the 211, 193, and 171 Å passbands. The prominence associated with each cavity is best seen in the 304 Å synoptic maps. We also estimate the thermal properties of the cavity and surrounding plasma by combining the AIA radiances with a differential emission measure analysis. This paper focuses on one long cavity from a catalog of coronal cavities that we are developing. Cavities in this catalog are designated by a coded name using the Carrington Rotation number and position. Cavity C211347177N was observed during Carrington Rotation 2113 at the northwestern limb of the solar disk with an average latitude of 47? N and a central longitude of 177?. We showed the following. (1) The cavity is a long tube with an elliptical cross-section with ratios of the length to width and the length to height of 11:1 and 7:1, respectively. (2) The cavity is about 1360 Mm long, or 170? in longitude. (3) It is tilted in latitude. (4) And it is slightly hotter than its surroundings.

Authors: N. Karna, J. Zhang, W. Dean Pesnell, and S. A. Hess Webber
Projects: SDO-AIA,SDO-HMI

Publication Status: Published (Sep 8, 2015)
Last Modified: 2015-09-14 16:09
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APPEARANCES AND STATISTICS OF CORONAL CAVITIES DURING THE ASCENDING PHASE OF SOLAR CYCLE 24
STUDY OF THE 3D GEOMETRIC STRUCTURE AND TEMPERATURE OF A CORONAL CAVITY USING THE LIMB SYNOPTIC MAP METHOD

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