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SUMMARY:Transverse Oscillations of Coronal Loops: Statistics\, Behaviour -
  Valery Nakariakov (Warwick)
DTSTART:20161107T160000Z
DTEND:20161107T170000Z
UID:TALK67414@talks.cam.ac.uk
CONTACT:Robert Teed
DESCRIPTION:Transverse (kink) oscillations of coronal loops are intensivel
 y studied as one of the main tools for coronal seismology. Recent observat
 ional findings led to the major progress in our understanding of this phen
 omenon. The oscillations appear in two different regimes\, the 169 decayin
 g oscillations and 72 undamped oscillations allow us to demonstrate that i
 n both regimes the oscillation periods are proportional the loop length.  
 This finding\, together with the independence of the oscillation amplitude
  on the period exclude the hypothesis that the oscillations are linked wit
 h the leakage of p-modes or other narrowband photospheric waves\, and supp
 ort the interpretation in terms of standing fast magnetoacoustic oscillati
 ons. In the decaying regime the loop displacement reaches several minor ra
 dii of the loop\, and the oscillation decays in typically a few oscillatio
 n cycles. In the majority of cases\, decaying kink oscillations are found 
 to be excited by low coronal eruptions. The quality factor is found to be 
 proportional to the oscillation amplitude\, indicating the nonlinear natur
 e of the damping. In the decayless regime the amplitude is usually lower t
 han the loop’s minor radius\, and remains constant or low-varying for a 
 number of oscillation cycles. The same loop may oscillate in both these re
 gimes\, e.g. before and after some impulsive excitation. The oscillation p
 eriod remains the same in both regimes. Low-amplitude undamped kink oscill
 ations are observed continuously\, without any visible source. We propose 
 that undamped kink oscillations of coronal loops may be caused by the inte
 raction of the loops with quasi-steady flows\, and hence are self-oscillat
 ions\, which is analogous to producing a tune by moving a bow across a vio
 lin string.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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