Uchida’s Theory of Magnetohydrodynamic Wave Refraction in an Inhomogeneous Medium: Testing the Theory with In Situ Measurements

Abstract Uchida’s paper describes a theory of MHD wave propagation in an inhomogeneous medium. In theory, waves encountering spatial structures (such as active regions, coronal holes, and coronal streamers) should be refracted/reflected. In the solar corona, MHD waves are predicted to refract away from (or into ) a structure, if the Alfvén speed V A increases ( decreases ) as the wave enters the structure. However, testing Uchida’s theory in the corona requires that local densities n i and field strengths B (required to calculate V A ) must be estimated indirectly. This limits significantly the reliability of testing Uchida’s theory in the corona. I suggest that, to better test the theory, a different medium should be explored, specifically, one where V A can be precisely evaluated in situ. The solar wind is such a medium. A recent data set allows testing Uchida’s theory over a broad range of times (~2 solar cycles) and radial locations (~2.5–5.4 au).