An Observationally Constrained 3D Potential-Field Source-Surface Model for The Evolution of Longitude-Dependent Coronal Structures

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Thursday, December 28, 2017

Mausumi Dikpati explains the challenge of creating synoptic maps of the photosphere that reliably reflect conditions at all locations concurrently is a major limitation to progress in this area.

Model For The Evolution Of Longitude-Dependent Coronal Structures image
Model output from the analysis of Carrington rotation 1912. With all other coefficients held constant, the adjustment of the g21 coefficient is shown. There is a distinct difference in the structure of the west (right) limb when the coefficient is adjusted by ±0.1, such that coefficient fluctuations of this magnitude represent a noticeable evolution of global structure from one Carrington rotation to the next.

White-light coronal images, which contain morphological information about the 3D corona at the solar limb, have been largely overlooked as a resource for constraining or correcting synoptic maps. We explore a complementary approach to traditional magnetogram-based coronal field solutions that makes use of these images. Applying a modified 3D PFSS model, we investigate the use of white-light coronal images from Mauna Loa Solar Observatory for deriving 3D coronal morphology by empirically fitting model- solutions with observations only. Applying an iterative technique to coronal image data from the solar minima preceding Cycles 22, 23, and 24, and the ascending phase of Cycle 23, we obtain model solutions as linear combinations of low order and degree spherical harmonics. We find that the 3D morphology produced by our method agrees qualitatively with traditional magnetogram-based PFSS approaches for coronas that are dipole dominated. For more complex coronas, additional constraints are needed to account for polarity and correct interpretation of coronal structures.

Publication Name: ApJ