4b.4 a Large Eddy Simulation Model of High Wind Marine Boundary Layers above a Spectrum of Resolved Moving Waves

An improved understanding of the interaction of winds, waves, and currents in the upper ocean at scales of individual waves and wave groups is needed to further develop the next generation of climate, weather, and wave forecast models. For example, coupled wind-waveocean models (Chen et al., 2007; Black et al., 2007) are viewed as critical tools for accurate prediction of tropical cyclone intensity and track forecasts, but these modeling systems employ a suite of parameterizations that are largely statistical descriptions of the wind-wave interactions that generate the critical momentum and scalar fluxes. These forecast models do not account for the important phase relationships between winds, waves and currents, e.g., the spatial and temporal intermittency of wave breaking that occurs in moderate to high winds (see figure 1). Also, there is a growing appreciation that wave-current interactions are important for the upper ocean boundary layer (Sullivan and McWilliams, 2010), and thus for climate predictions, and that remotely generated swell and non-equilibrium wave states can play an important and critical role in the surface-layer dynamics of the atmospheric planetary boundary layer (PBL) (Hanley et al., 2010; Sullivan and McWilliams, 2010). The present work describes our recent developments in coupling a turbulence-resolving large-eddy simulation (LES) of the atmospheric PBL to a three-dimensional time-dependent resolved surface wavefield. This builds on our past efforts which coupled a turbulent boundarylayer flow with a single monochromatic wave (Sullivan et al., 2000; Sullivan and McWilliams, 2002; Sullivan et al., 2008). The computational method described here allows for nearly arbitrary 3D wavefields, i.e., the sea surface elevation h = h(x,y, t), as a surface boundary condition. The spatial scales of the resolved turbulence and waves are O(m) up to the scale of the PBL height. At present, the waves are externally imposed based on empirical wave spectra. Ultimately the wavefields will