On the existence of simple waves for two-dimensional non-ideal magneto-hydrodynamics

In this article, a method called characteristic decomposition is used to show the presence of simple waves for the two-dimensional compressible flow in a non-ideal magneto-hydrodynamics system. Here, a steady and pseudo-steady state magneto-hydrodynamics system is considered, and we provide a characteristic decomposition of the flow equations in both systems. This decomposition ensures the presence of a simple wave adjacent to a region of constant state for the system under consideration. Further, this result is extended as an application of the characteristic decomposition in a pseudo-steady state, and we prove the existence of a simple wave in a full magneto-hydrodynamics system by taking the vorticity and the entropy to be constant along the pseudo-flow characteristics. These results extend the fundamental theorem proposed by Courant and Friedrichs for a reducible system (R. Courant and K. O. Friedrichs, Supersonic Flow and Shock Waves, New York, Interscience Publishers, Inc., 1948, p. 464). A motivational work was carried out for an ideal gas by Li et al. ("Simple waves and a characteristic decomposition of the two dimensional compressible Euler equations," Commun. Math. Phys. Math. Phys., vol. 267, no. 1, pp. 1-12, 2006) and for a non-ideal gas by Zafar and Sharma ("Characteristic decomposition of compressible Euler equations for a non-ideal gas in two-dimensions," J. Math. Phys., vol. 55, no. 9, pp. 093103-093112, 2014], [M. Zafar, "A note on characteristic decomposition for two-dimensional euler system in van der waals fluids," Int. J. Non-Linear Mech., vol. 86, pp. 33-36, 2016].