Title: Wave breaking and dissipation in the presence of long waves: what can we guess from spectral shapes?

Wave breaking is the largest sink of wind-wave energy and plays a very important role in setting the energy level of wind-generated waves and in many other geophysical effects, 
including air-sea interaction. Following Phillips (1984), many efforts have been made to define the spectral distribution of wave dissipation from the distribution of breaking fronts and 
a dissipation rate per length of breaking front. One key difficulty is the parameterization of the effects of one particular spectal component on the dissipation rate of another. 
Recently, Romero (2019) proposed a parameterization of breaking fronts from the wave spectrum that treats all wave directions independently, except for an effect of long waves 
facilitating the breaking of shorter waves. In particular, long waves have zero effect on the dissipation rate of waves propagating 90° away from the main direction, 
and a large effect on waves propagating down-wind. This is the first parameterization that is able to reproduce some of the directional properties of the short waves as measured by 
a few stereo-video experiments and extensive underwater acoustic data. The fact that this model works and many others don't, does it tell us something about how waves break and how 
the breaking of long or short waves affects the dissipation of short waves?  In particular, Romero (2019) quantified the effect of long waves with a "cumulative mean square slope" borrowed 
from Donelan and a main direction that is energy-weighted. We will in particular discuss the impact of these two choices, and how the model can be improved by taking a different combination 
of long wave properties, for example with an orbital velocity amplitude instead of a mean square slope, and a main direction that is also associated with orbital velocities. 
These model tests suggest that in would be very interesting to analyse the breaking and dissipation rate of waves in the presence of one or two other longer wave trains.