Coronal Cooling as a Result of Mixing by the Nonlinear Kelvin-Helmholtz Instability

Recent observations show cool, oscillating prominence threads fading when observed in cool spectral lines and appearing in warm spectral lines. A proposed mechanism to explain the observed temperature evolution is that the threads were heated by turbulence driven by the Kelvin-Helmholtz instability that developed as a result of wave-driven shear flows on the surface of the thread. As the Kelvin?Helmholtz instability is an instability that works to mix the two fluids on either side of the velocity shear layer, in the solar corona it can be expected to work by mixing the cool prominence material with that of the hot corona to form a warm boundary layer. In this paper, we develop a simple phenomenological model of nonlinear Kelvin?Helmholtz mixing, using it to determine the characteristic density and temperature of the mixing layer. For the case under study, with constant pressure across the two fluids, these quantities are