The Transient IDEMIX Model as a Nonorographic Gravity Wave Parameterization in an Atmospheric Circulation Model

The Internal wave Dissipation, Energy and Mixing (IDEMIX) model presents a novel way of parameterizing internal gravity waves in the atmosphere. Using a continuous full wave spectrum in the energy balance equation and integrating over all vertical wavenumbers and frequencies results in prognostic equations for the energy density of gravity waves in multiple azimuthal compartments. It includes their non-dissipative interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag (GWD). A saturation mechanism maintains the wavefield within convective stability limits, and an energetically consistent closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. IDEMIX can simulate zonal GWD around the mesopause, similar to a traditional gravity wave parameterization and to a state-of-the-art wave ray tracing model in an atmospheric circulation model. In addition, IDEMIX shows a reversal of the GWD around the mesopause region due to interaction with the mean flow there. When compared to empirical model data, IDEMIX captures well the summer hemisphere flow reversal, the cold summer mesospheric pole and the alternate positive and negative structures in the meridional mean flow.