A New Insight into the Linear Theory of Magnetoacoustic Waves in the Homogeneous Flux Tubes with an Abrupt Boundary

Abstract

An important and interesting issue is brought to notice in the standard linear theory of the magnetoacoustic waves in the homogeneous magnetic flux tubes with an abrupt magnetic boundary, which are representative of the coronal, chromospheric, and photospheric loops of the solar atmosphere. It is shown that the dispersion relation given for the magnetoacoustic waves of such flux tubes by the linear standard theory is generally inapplicable because it does not take into account the electrodynamic boundary condition and the applicability is only restricted to the case β = 0, where β is the usual plasma parameter given by the ratio of the thermodynamic gas pressure to the magnetic pressure. This issue is then addressed, which gives us new insight into the standard linear theory of such modes, and a new dispersion relation is obtained, which is generally applicable i.e., for all β and would reduce to the earlier expression as a special case for β = 0. Finally a comparison is drawn between the dispersion curves described by the newly derived dispersion relation and its previous counterpart.