Spontaneous wave emission by flows is a viable route to dissipation. For quasi-balanced flows, characterized by a small Rossby number, the amplitudes of emitted waves are expected to be small. However, once being emitted into a three-dimensional eddying flow field, waves can undergo refraction and may be "captured." During wave capture, the wavenumber grows exponentially, ultimately leading to breakup and dissipation. For flows with not too small Rossby number, e.g. for flows in the vicinity of strong fronts, dissipation occurs in a more complex manner. It can occur via spontaneous wave emission and the subsequent wave capture, with the amplitudes of waves emitted in frontal systems being expected to be larger than amplitudes of waves emitted by quasi-balanced flows. It can also occur through turbulence and filamentation emerging from frontogenesis.
So far, quantitative importance of this energy pathway - crucial for determining correct eddy viscosities in general circulation models - is not known. Toward an answer to this question, we discuss IGWs diagnostics, review spontaneous emission of both quasi-balanced and less-balanced frontal flows, and discuss recent numerical results based on a high-resolution ocean general circulation model. tion and as a departure point for original research in the field.