W6: Spectral Energy Fluxes by Wave-Wave Interactions

The two main wave modes − gravity waves and Rossby waves − govern the circulation in atmosphere and ocean. Although their linear properties are well understood, the role of wave-wave interactions is unknown to a large extent, but it is certainly of major importance for energy transfers in the atmosphere and ocean. In both the atmosphere and ocean, the energy exchange is governed by the same mechanism of the triad interactions, which this subproject aims at understanding better.
An improved understanding will be achieved by focusing on the nonlinear interactions involving

1.  internal gravity waves and Rossby waves in the mid-latitude ocean, and
2. the most energetic waves in the tropical atmosphere.

By focusing on the two unique dynamical regions on the globe – the tropics and mid-latitudes – and by sharing ideas, methods and cross-validation, the results of this subproject will underline not only the energy transfers within and between different wave types but also the transfer to small-scale turbulence by wave breaking in the ocean, from the tropics to extratropics, and from the troposphere to the middle atmosphere.
Better understanding and quantification will contribute to improvements in:

1. parameterizations of wave-wave interactions (subprojects W1, W4, W2, S2)
2. interpretation of regime decomposition and momentum fluxes (L2)
3. quantification of the energy cycle in the ocean and atmosphere (W2, L2), and 4) model evaluation using novel metrics (S1)

Furthermore, wave interactions in the tropics and their intimate coupling to convection will contribute new understanding towards balance theory for the tropics.