Large eddy simulation of high wind marine boundary layers above a spectrum of resolved moving waves

The marine atmospheric boundary layer is impacted by the presence of a surface gravity wave field at scales ranging from centimeters (surface roughness) to hundreds of meters (remotely generated swell). Surface waves modulate the air-water interface fluxes of momentum and scalars and thus influence the overall forcing of the atmospheric boundary layer. Recently, we have coupled our LES code of the marine boundary layer with a 3-D time-evolving surface wavefield. The LES algorithm utilizes a co-located variable layout that permits large waveslope at the sea surface, a moving wave-following mesh, and an iterative solution of the pressure Poisson equation. Special care is taken to ensure that the grid conservation law for moving meshes is satisfied. The moving mesh mechanics are embedded in a highly parallelized LES code. We utilize this code to examine boundary layer dynamics over a windspeed range from [5-20] m/s with the prescribed wave surface given by a truncated Pierson-Moskowitz wave height field with a directional spectrum that emphasizes long-crested waves. The results further highlight the interesting features of non-equilibrium wind-wave conditions and in particular the competition between near irrotational motions induced by surface wave pumping and turbulence. The wave induced pressure field is found to change markedly over the wind speed range considered.