THE SPRAY CONTRIBUTION TO NET EVAPORATION FROM THE SEA: A REVIEW OF RECENT PROGRESS EDGAR L ANDREAS, I JAMES B. EDSON, ~ EDWARD C. MONAHAN, 3, MATHIEU R ROUAULT, 4 and STUART D. SMITH 5 1U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755, U.S.A.; 2Department of Applied Ocean Physics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, U.S.A.; 3Marine Sciences Institute, University of Connecticut at Avery Point, Groton, Connecticut 06340, U.S.A.; 4Department of Oceanography, University of Cape Town, 7700 Rondebosch, Republic of South Africa; 5Department of Fisheries and Oceans, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada (Received in final form 18 May, 1994) Abstract. The part that sea spray plays in the air-sea transfer of heat and moisture has been a controversial question for the last two decades. With general circulation models (GCMs) suggesting that perturbations in the Earth's surface heat budget of only a few W m -2 can initiate major climatic variations, it is crucial that we identify and quantify all the terms in that heat budget. Thus, here we review recent work on how sea spray contributes to the sea surface heat and moisture budgets. In the presence of sway, the near-surface atmosphere is characterized by a droplet evaporation layer (DEL) with a height that scales with the significant-wave amplitude. The majority of spray transfer processes occur within this layer. As a result, the DEL is cooler and more moist than the atmospheric surface layer would be under identical conditions but without the spray. Also, because the spray in the DEL provides elevated sources and sinks for heat and moisture, the vertical heat fluxes are no longer constant with height. We use Eulerian and Lagrangian models and a simple analytical model to study the processes important in spray droplet dispersion and evaporation within this DEL. These models all point to the conclusion that, in high winds (above about 15 m/s), sea spray begins to contribute significantly to the air-sea fluxes of heat and moisture. For example, we estimate that, in a 20-m/s wind, with an air temperature of 20~ a sea surface temperature of 22~ and a relative humidity of 80%, the latent and sensible heat fluxes resulting from the spray alone will have magnitudes of order 150 and 15 W/m 2, respectively, in the DEL. Finally, we speculate on what fraction of these fluxes rise out of the DEL and, thus, become available to the entire marine boundary layer. 1. Introduction Pioneers such as Bortkovskii (1973, 1983, 1987), Borisenkov (1974), Wu (1974), and Ling (Ling and Kao, 1976; Ling et al., 1978, 1980), who tried to estimate the contribution of sea spray droplets to evaporation from the sea surface, faced many uncertainties. For example, they did not have reliable estimates of the flux of spray droplets up from the ocean surface and did not have a clear understanding of how evaporation from spray droplets modifies the temperature and humidity profiles in the lower marine boundary layer. Although we have learned much about these processes in the last decade, many uncertainties remain. The field is, therefore, still rife with controversy because experimental work is difficult, the processes are complex and interactive, and theories of sea spray generation and heat and moisture transfer by spray are still rudimentary. The recent exchanges in the literature between Monahan and Woolf Boundary-Layer Meteorology 72: 3-52, 1995. @ 1995 Kluwer Academic Publishers~ Printed in the Netherlands.