There are three basic MHD waves: an incompressible Alfvén wave and a fast and slow magnetoacoustic waves, which are both essentially compressible. Properties of MHD waves strongly depend upon the angle between the wave vector and the magnetic field, consequently, MHD waves are highly affected by plasma structuring and filamentation. Structuring of the solar coronal plasma modifies those waves and may lead to their coupling, bringing such interesting features of MHD wave dynamics as phase mixing, resonant absorption, and guided wave propagation, dramatically influencing manifestation of the waves in observations. This makes the theory of MHD wave modes of plasma structures to be the key ingredient of the coronal wave study. Also, the theory provides the necessary classification of wave and oscillatory phenomena in coronal plasmas.
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