Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.9112c&link_type=abstract
American Astronomical Society Meeting 210, #91.12; Bulletin of the American Astronomical Society, Vol. 39, p.206
Astronomy and Astrophysics
Astronomy
Scientific paper
Damped oscillations of solar coronal loops observed with high spatial and temporal resolution have recently been used to infer resistive and viscous dissipation rates in the corona. Assuming that the damping is dominated by coronal resistivity and viscosity inside coronal loops, the coronal Reynolds number, Rv, and Lundquist number, S, have been estimated to approximately eight orders of magnitude smaller than the classical values. We propose an alternative ideal magnetohydrodynamic (MHD) model of damped oscillation in which the energy of oscillation is coupled to that of the coronal plasmas via drag. The loop structure is assumed to be a flux rope embedded in a corona of finite pressure, have stationary photospheric footpoints, and carry toroidal and poloidal currents. It is shown that the theory can accurately explain the observed damped oscillations. The value of the drag coefficient cd required to obtain the observed damping rate is found to be cd ≈ 2-8, depending on parameters such as the loop density, ambient magnetic field, and loop geometry. This range of values is similar to that obtained in a previous MHD simulation study and is consistent with the values used to reproduce observed trajectories of coronal mass ejections. In the present ideal MHD calculation, we have Rv, S = ∞. This result shows that observed damped oscillations can be explained using the classical value of resistivity and a reasonable drag coefficient. The Lorentz force, pressure gradient force, and drag force are calculated.
Work supported by ONR and NASA
Chen James
Schuck Peter W.
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