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Magnetic helicity condensation and the solar cycle

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Mackay_2018_ApJ_869_62.pdf (8.410Mb)
Date
12/2018
Author
Mackay, Duncan Hendry
DeVore, C. Richard
Antiochos, Spiro
Yeates, Anthony Robinson
Funder
Science & Technology Facilities Council
Science & Technology Facilities Council
The Leverhulme Trust
Grant ID
ST/K000950/1
ST/N000609/1
RPG-305
Keywords
Sun: activity
Sun: corona
Sun: magnetic fields
QB Astronomy
QC Physics
NDAS
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Abstract
Solar filaments exhibit a global chirality pattern where dextral/sinistral filaments, corresponding to negative/positive magnetic helicity, are dominant in the northern/southern hemisphere. This pattern is opposite to the sign of magnetic helicity injected by differential rotation along east-west oriented polarity inversion lines, posing a major conundrum for solar physics. A resolution of this problem is offered by the magnetic helicity condensation model of Antiochos (2013). To investigate the global consequences of helicity condensation for the hemispheric chirality pattern, we apply a temporally and spatially averaged statistical approximation of helicity condensation. Realistic magnetic field configurations in both the rising and declining phases of the solar cycle are simulated. For the helicity condensation process, we assume convective cells consisting of positive/negative vorticities in the northern/southern hemisphere, which inject negative/positive helicity. The magnitude of the vorticity is varied as a free parameter, corresponding to different rates of helicity injection. To reproduce the observed percentages of dominant and minority filament chiralities, we find that a vorticity of magnitude 2.5 x 10-6 s-1 is required. This rate, however, is insufficient to produce the observed unimodal profile of chirality with latitude. To achieve this, a vorticity of at least 5 x 10-6 s-1 is needed. Our results place a lower limit on the small-scale helicity injection required to dominate differential rotation and reproduce the observed hemispheric pattern. Future studies should aim to establish whether the helicity injection rate due to convective flows and/or flux emergence across all latitudes of the Sun is consistent with our results.
Citation
Mackay , D H , DeVore , C R , Antiochos , S & Yeates , A R 2018 , ' Magnetic helicity condensation and the solar cycle ' , Astrophysical Journal , vol. 869 , no. 1 , 62 . https://doi.org/10.3847/1538-4357/aaec7c
Publication
Astrophysical Journal
Status
Peer reviewed
DOI
https://doi.org/10.3847/1538-4357/aaec7c
ISSN
0004-637X
Type
Journal article
Rights
© 2018, American Astronomical Society. This work has been made available online in accordance with the publisher's policies. This is the final published version of the work, which was originally published at https://doi.org/10.3847/1538-4357/aaec7c
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  • University of St Andrews Research
URI
http://hdl.handle.net/10023/16694

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