Volume 619, November 2018
|Number of page(s)||10|
|Published online||22 November 2018|
Resonant damping of kink oscillations of thin cooling and expanding coronal magnetic loops
1 Solar Physics and Space Plasma Research Centre (SP 2RC), University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7R, UK
2 ITMO University, Kronverkskii ave 49, 197101 Saint-Petersburg, Russia
3 Space Research Institute (IKI), Russian Academy of Sciences, Moscow 117810, Russia
4 Dept of Astronomy, Eötvös L. University, Pázmány P. sétány 1/A, Budapest 1117, Hungary
Accepted: 12 September 2018
We have considered resonant damping of kink oscillations of cooling and expanding coronal magnetic loops. We derived an evolutionary equation describing the dependence of the oscillation amplitude on time. When there is no resonant damping, this equation reduces to the condition of conservation of a previously derived adiabatic invariant. We used the evolutionary equation describing the amplitude to study the competition between damping due to resonant absorption and amplification due to cooling. Our main aim is to investigate the effect of loop expansion on this process. We show that the loop expansion acts in favour of amplification. We found that, when there is no resonant damping, the larger the loop expansion the faster the amplitude growths. When the oscillation amplitude decays due to resonant damping, the loop expansion reduces the damping rate. For some values of parameters the loop expansion can fully counterbalance the amplitude decay and turn the amplitude evolution into amplification.
Key words: hydrodynamics / magnetohydrodynamics (MHD) / plasmas / waves / methods: analytical / Sun: corona
© ESO 2018
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