Within the marine boundary-layer, wind-wave formation, aerosol production and processing, dynamics, and thermodynamics represent a set of coupled processes controlling mass, heat and momentum exchange between the atmosphere and ocean with cumulative effects across all scales of the system. The structure of the ocean wind-wave field has a wind-speed and stability dependent impact on the surface drag coefficient and associated vertical wind profile. The entrainment of air by breaking waves modulate gas transfer of several climate-relevant species and generates marine aerosols that contain highly reactive organic and inorganic constituents. These processes have major implications for local, regional, and global chemistry; the microphysical properties of clouds; and radiative transfer. This - directly (through latent heating/cooling) and indirectly (via interactions with atmospheric radiation and clouds) - impacts the composition and structure of the marine boundary layer. At high wind speeds (>20 m s-1, the formation of larger marine aerosols by bursting bubbles and the tearing of wave crests is hypothesized to influence the latent and sensible heat and water vapor content of the boundary layer, as well as atmospheric stability and turbulence in the boundary layer. The ability to accurately reliably simulate these processes and to account for their interrelated impacts on climate and climate extremes requires that the ocean wind-wave field be modeled explicitly. To date, this has not been done within fully coupled Earth System Models (ESM). In cooperation with several ongoing research efforts at National Center for Atmospheric Research, the University of Colorado at Boulder (Baylor Fox-Kemper), and Oak Ridge National Laboratory ( David Erickson), and Pacific Northwest National Lab (Steven Ghan, Xiaohong Liu, Paul Rasch) we will leverage new, unique observations of wind-wave generation and breaking, gas and heat exchange, and aerosol production at the ocean surface to develop and implement a more realistic yet numerically efficient treatment of air-se interaction, boundary-layer processes, and associated climatic interactions in the CESM. Accurate representation of the nonlinear processes associated with the air-sea interface is a critical prerequisite for reliable climate prediction, the accurate resolution of extreme climate events, and bridging the gap between observed and simulated regional climate. Results of the proposed research effort will substantially enhance the CESM and thereby contribute directly to the Biological and Environmental Research (BER) Climate and Environmental Sciences Division (CESD) Long Term Measure.
The two-year investigation proposed herein will address the following objective. (1) A wave-side module will be developed to calculate relevant wave parameters for the atmosphere module. (2) Drawing on input from the wave-side module, a three-component atmosphere-side module will be developed to calculate size- and composition-resolved marine aerosol production, transport and processing and associated influences on boundary-layer structure and evolution. (2a) Develop a parameterization for the production of size- and composition-resolved marine aerosols as a function of the state of the wind-wave field via bubble bursting and tearing of wave crests. (2b) Incorporate a total air-sea (sensible and latent heat from interfacial and spume droplet fluxes) enthalpy transfer algorithm into CAM. (2c) Incorporate the parameterization for the calculation of wind-wave form-drag, surface roughness, and momentum exchange coefficient for boundary layer formation and evolution. (3) Coupled model testing and tuning, and production-run simulations will be executed through a combination of (3a) CAM in single-column (1-D vertical) mode with offline ocean and wave forcing, (3b) climate-scale ensemble simulations of the fully coupled CESM, and (3c) modal-aerosol CAM coupled with the CAABA/MECCA pH-resolving aqueous chemistry mechanism to assess the impact of the wind-wave driven marine aerosol fields on CH4, O3, OH, DMS and inorganic N and S chemistry in the marine boundary layer and global troposphere and the associated impact on radiative transfer, clouds, precipitation and climate. The set of coupled modules will significantly improve CESM performance.