A simplified approach to internal gravity wave damping by viscous dissipation

Abstract

Internal gravity wave perturbation velocity subject to constant dynamic viscosity and constant kinematic viscosity are approximately derived based on an energy conservation principle. When the dynamic viscosity is assumed to be a constant, the velocity at any height relative to the velocity at the saturation height, Z sat, is found to be solely dependent on the number of scale heights measured from Z sat. Gravity wave energy dissipation due to constant dynamic viscosity primarily occurs from one scale height below to one scale height above the saturation height. When the kinematic viscosity is assumed to be a constant, the perturbation amplitude either increases or decreases monotonically with height depending on whether the energy dissipation rate due, to viscosity, can offset the effect of the decreasing atmospheric density with increasing height. The derivations are made simple by assuming that the non-dissipative dispersion relation is applicable to the dissipative situation. The condition for the assumption to be approximately valid is also given.