  The solar atmosphere is known to contain many different types of wavelike
oscillation. Waves and other fluctuations (e.g., turbulent eddies) are believed
to be responsible for at least some of the energy transport and dissipation
that heats the corona and accelerates the solar wind. Thus, it is important to
understand the behavior of magnetohydrodynamic (MHD) waves as they propagate
and evolve in different regions of the Sun's atmosphere. In this paper, we
investigate how MHD waves can affect the overall plasma state when they reflect
and refract at sharp, planar interfaces in density. First, we correct an error
in a foundational paper (Stein 1971) that affects the calculation of wave
energy-flux conservation. Second, we apply this model to reflection-driven MHD
turbulence in the solar wind, where the presence of density fluctuations can
enhance the generation of inward-propagating Alfven waves. This model
reproduces the time-averaged Elsasser imbalance fraction (i.e., ratio of inward
to outward Alfvenic power) from several published numerical simulations.
Lastly, we model how the complex magnetic field threading the transition region
between the chromosphere and corona helps convert a fraction of
upward-propagating Alfven waves into fast-mode and slow-mode MHD waves. These
magnetosonic waves dissipate in a narrow region around the transition region
and produce a sharp peak in the heating rate. This newly found source of
heating sometimes exceeds the expected heating rate from Alfvenic turbulence by
an order of magnitude. It may explain why some earlier models seemed to require
an additional ad-hoc heat source at this location.

Solar and Stellar Astrophysics;Plasma Physics;Space Physics