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Solar oblateness & asphericities temporal variations: Outstanding some unsolved issues

Published online by Cambridge University Press:  24 September 2020

Jean P. Rozelot Open the ORCID record for Jean P. Rozelot [Opens in a new window] ,
Alexander G. Kosovichev  and
Ali Kilcik
Jean P. Rozelot
Affiliation:
1Université Côte d'Azur, 77 Chemin des Basses Moulières, 06130 Grasse, France email: [email protected]
Alexander G. Kosovichev
Affiliation:
2Center for Computational Heliophysics and Department of Physics, New Jersey Institute of Technology, Newark, NJ07102, USA email: [email protected]
Ali Kilcik
Affiliation:
3Akdeniz University Faculty of Science, Department of Space Science and Technologies, 07058, Antalya, Turkey email: [email protected]
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Abstract

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Solar oblateness has been the subject of several studies dating back to the nineteenth century. Despite difficulties, both theoretical and observational, tangible results have been achieved. However, variability of the solar oblateness with time is still poorly known. How the solar shape evolves with the solar cycle has been a challenging problem. Analysis of the helioseismic data, which are the most accurate measure of the solar structure up to now, leads to the determination of asphericity coefficients which have been found to change with time. We show here that by inverting even coefficients of f-mode oscillation frequency splitting to obtain the oblateness magnitude and its temporal dependence can be inferred. It is found that the oblateness variations lag the solar activity cycles by about 3 years. A major change occurred between solar cycles 23 and 24 is that the oblateness was greater in cycle 24 despite the lower solar activity level. Such results may help to better understand the near-subsurface layers as they strongly impacts the internal dynamics of the Sun and may induce instabilities driving the transport of angular momentum.

Keywords

Sun: heliosismologySun: activitySun: rotationSun: fundamental parameters
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 15 , Symposium S354: Solar and Stellar Magnetic Fields: Origins and Manifestations , June 2019 , pp. 232 - 237
Copyright
© International Astronomical Union 2020

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