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Modeling observed decay-less oscillations as resonantly enhanced Kelvin-Helmholtz vortices from transverse MHD waves and their seismological application

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Antolin_2016_Modelling_ApJL_AAM.pdf (3.851Mb)
Date
12/10/2016
Author
Antolin, P.
De Moortel, Ineke
Van Doorsselaere, T.
Yokoyama, T.
Keywords
Magnetohydrodynamic (MHD)
Sun: activity
Sun: corona
Sun: oscillations
QB Astronomy
QC Physics
T-NDAS
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Abstract
In the highly structured solar corona, resonant absorption is an unavoidable mechanism of energy transfer from global transverse MHD waves to local azimuthal Alfvén waves. Due to its localised nature, a direct detection of this mechanism is extremely difficult. Yet, it is the leading theory explaining the observed fast damping of the global transverse waves. However, at odds with this theoretical prediction, recent observations indicate that in the low amplitude regime such transverse MHD waves can also appear decay-less, a yet unsolved phenomenon. Recent numerical work has shown that Kelvin-Helmholtz instabilities (KHI) often accompany transverse MHD waves. In this work, we combine 3D MHD simulations and forward modelling to show that for currently achieved spatial resolution and observed small amplitudes, an apparent decay-less oscillation is obtained. This effect results from the combination of periodic brightenings produced by the KHI and the coherent motion of the KHI vortices amplified by resonant absorption. Such effect is especially clear in emission lines forming at temperatures that capture the boundary dynamics rather than the core, and reflects the low damping character of the local azimuthal Alfvén waves resonantly coupled to the kink mode. Due to phase mixing, the detected period can vary depending on the emission line, with those sensitive to the boundary having shorter periods than those sensitive to the loop core. This allows to estimate the density contrast at the boundary.
Citation
Antolin , P , De Moortel , I , Van Doorsselaere , T & Yokoyama , T 2016 , ' Modeling observed decay-less oscillations as resonantly enhanced Kelvin-Helmholtz vortices from transverse MHD waves and their seismological application ' , Astrophysical Journal Letters , vol. 830 , no. 2 , L22 . https://doi.org/10.3847/2041-8205/830/2/L22
Publication
Astrophysical Journal Letters
Status
Peer reviewed
DOI
https://doi.org/10.3847/2041-8205/830/2/L22
ISSN
2041-8205
Type
Journal item
Rights
© 2016, American Astronomical Society. This work is made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at http://dx.doi.org/10.3847/2041-8205/830/2/L22
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  • University of St Andrews Research
URL
http://adsabs.harvard.edu/abs/2016ApJ...830L..22A
URI
http://hdl.handle.net/10023/9577

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