Short Quasi-Periodic MHD Waves in Coronal Structures |
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Authors: | V M Nakariakov D J Pascoe T D Arber |
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Institution: | (1) Physics Department, University of Warwick, Coventry, CV4 7AL, UK |
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Abstract: | The possibility of remote diagnostics of coronal structures with impulsively-generated short-period fast magnetoacoustic wave
trains is demonstrated. An initially broad-band, aperiodic fast magnetoacoustic perturbation guided by a 1D plasma inhomogeneity
develops into a quasi-periodic wave train with a well-pronounced frequency and amplitude modulation. The quasi-periodicity
results from the geometrical dispersion of the modes, determined by the transverse profile of the loop, and hence contains
information about the profile. Wavelet images of the wave train demonstrate that their typical spectral signature is of a
“crazy tadpole’’ shape: a narrow spectrum tail precedes a broad-band head. The instantaneous period of the oscillations in
the wave train decreases gradually with time, with a mean value of several seconds for typical coronal values. The period
and the spectral amplitude evolution are determined by the steepness of the transverse density profile and the density contrast
ratio in the loop, which offers a tool for estimation of the sub-resolution structuring of the corona. |
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Keywords: | coronal seismology coronal waves MHD solar corona |
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