A new parameterization of gravity waves for atmospheric circulation models based on the radiative transfer equation

Gravity waves play an important role in the momentum and heat budgets of the middle atmosphere. Global circulation models used for long-term simulations need to parameterize the transport of wave momentum and energy from the lower to the middle atmosphere and the associated wave-mean flow interaction. This gravity wave-mean flow interaction is usually due to dynamical instability triggered by wave refraction and amplitude growth, giving rise to wave dissipation. In addition, gravity waves can interact with the mean flow through the passage of finite wave packets without dissipation. Conventional gravity wave parameterizations cannot describe this effect; nor can they account for wave sources being continuous in space and time, for the finite duration of vertical propagation, or wave acceleration induced by a temporally varying mean flow.
All these effects are accommodated when the wave field is described by the wave-energy density in wave number and physical space, and its evolution is computed by the radiative transfer equation for the wave field. A corresponding parameterization called IDEMIX has successfully been applied in ocean models. Here we present a corresponding parameterization for atmosphere models in single-column approximation. The new scheme is validated in off-line simulations. Results show that the evolution of wave packets forced in the troposphere and propagating upward into stratospheric and mesospheric jets is simulated consistently with theoretical expectations. This includes wave reflection and critical layers. Furthermore, an explicit diffusion scheme was added to account for wave dissipation due to dynamical instability.