Journal
ASTRONOMY & ASTROPHYSICS
Volume 379, Issue 3, Pages 1098-1105Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361:20011415
Keywords
magnetohydrodynamics (MHD); waves; Sun : activity; Sun : corona
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The interaction of a weakly nonlinear Alfvenic pulse with an Alfven speed inhomogeneity in the direction perpendicular to the magnetic field is investigated. Identical to the phase mixing experienced by a harmonic Alfven wave, sharp transverse gradients are generated in the pulse by the inhomogeneity. In the initial stage of the evolution of an initially plane Alfvenic pulse, the transverse gradients efficiently generate transversely propagating fast magnetoacoustic waves. However, high resolution full MHD numerical simulations of the developed stage of the pulse evolution show that the generation saturates due to destructive wave interference. It is shown that the weakly non-linear description of the generated fast magnetoacoustic wave is well described by the driven wave equation proposed in Nakariakov et al. (1997), and a simple numerical code (2D MacCromack), which solves it with minimal CPU resources, produces identical results to those obtained from the full MHD code (Lare2d, Arber et al. 2001). A parametric study of the phenomenon is undertaken, showing that, contrary to one's expectations, steeper inhomogeneities of the Alfven speed do not produce higher saturation levels of the fast wave generation. There is a certain optimal gradient of the inhomogeneity that ensures the maximal efficiency of the fast wave generation.
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