PROGRAM TITLE: Boundary Layer Dynamics, Marine Aerosols ACTIVITY STREAM: Process Studies SCIENCE ELEMENT:Biogeochemical Dynamics DEPARTMENT OF DEFENSE OFFICE OF NAVAL RESEARCH (ONR) SCIENTIFIC MERIT: This is a basic research effort to understand and quantify the physical and chemical mechanisms determining the size distribution and chemical constituents of marine aerosols and the dynamics of their evolution. Knowledge of the physical and chemical properties of marine aerosol particles is important because of the role these particles play in a number of important atmospheric processes. Marine aerosols affect radiative transfer and climate directly by scattering and absorbing radiation and indirectly by influencing the droplet size distribution and albedo of marine boundary layer clouds. In addition, the emissions of reduced sulfur gases from the oceans contribute significantly to the global sulfur cycle. The processes controlling the production and consumption of these reduced sulfur gases in the sea are poorly understood. A guiding principle is to achieve a mechanistic rather than empirical or correlational understanding of marine aerosol dynamics. Immediate objectives include determining the effects of: microphysical parameters on evolution of measured aerosol distributions, non-precipitating cloud cycling, and gas-to-particle conversion dynamics. The role of marine aerosols in cloud condensation nuclei dynamics and electro-optical extinction coefficient will be specifically targeted. This work will capitalize on and improve predictive models developed by DOE and DOD. Parallel efforts in the laboratory, field experiments, and a modeling component will address electro-optics problems impacting DOD communications, surveillance, and guidance issues while at the same time work the two highest priority Global Change science element problems. This program will provide new data and insight to the role of clouds and bio/atmosphere/ocean flux questions highlighted by the USGCRP. This research initiative has been approved by DOD and endorsed by the National Academy of Science. Several workshops were held to frame this program, and the federal and academic research communities have participated from the beginning. STAKEHOLDERS: Strong interaction with DOD laboratories and the academic communities is programmed. For example, transition routes from federal labs and academia are established with Air Force and Navy operational modeling community. This work will then support regional nested models made available to the Global Climate Modelers. A strong cooperative effort with DOE modelers involving evolution of aerosols from a point source is underway now. In addition to this program's emphasis on modeling and hence prediction of natural and human factors involved in the generation of cloud condensation nuclei, whose impacts on climate are still not well understood; the program interacts with US-JGOFS in helping to characterize the oceanic chemistry, particularly of the mixed layer. Participation in the US-JGOFS EQ-PAC experiment was highly contributive, participation in the Southern Ocean experiment is planned. POLICY RELEVANCE: One objective of this program is to provide better prediction of laser systems effectiveness in varying oceanographic and meteorological conditions. However, the same understanding contributes directly to the evaluation of climate change and natural and man-made variability. In particular, the program seeks to provide understanding of to what degree natural and man-made sulfur compounds contribute to cloud creation by providing cloud condensation nuclei and the relative roles of anthropogenic versus natural sources. PROGRAM CONTACT:Dr. Edward J. Green, ONR Code 323C, 800 N. Quincy Street, Arlington, VA 22217-5660, (703) 696-4591