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L. Ofman (Raytheon ITSS/NASA GSFC), V.M. Nakariakov (University of St Andrews), E. DeLuca (Harvard-Smithsonian Center for Astrophysics), B. Roberts (University of St Andrews), J.M. Davila (NASA GSFC)
The Transition Region and Coronal Expolorer (TRACE) observes the solar corona with unprecedented spatial and temporal resolution. We analyzed active region loop observation in the 171ÅFe IX emission line, and report the direct observations of damped transverse oscillations of a long (130±6 Mm) thin (diameter 2±0.36 Mm) bright active region loop. The oscillations were detected following a flare in the adjacent active region. We determined the oscillation frequency and the decay time by the least-square fit of an exponentially decaying sinusoidal function. Using the dispersion relation for the transverse oscillations, and the observed loop geometry we estimated the Alfvén crossing time in the loop. The Alfvén time can be used to determine the magnetic field strength in the loop if the density is known. All parts of the loop were observed to oscillate transversly in-phase, implying that the ocillation is a global mode of the loop. Using dissipative MHD model for resonant absorption of global mode oscillations for the coronal loop we determined the Reynolds number that produces the observed damping rate of the observed global mode. The value of the Reynolds number is in the 105-106 range, which is eight to nine orders of magnitude smaller than the classical coronal value. We discuss the important implication of the small Reynolds number on coronal heating theories.
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