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Abstract. This paper describes the various physical processes relating near-surface atmospheric and oceanographic bulk variables; their relationship to the surface fluxes of momentum, sensible heat, and latent heat; and their expression in a bulk flux algorithm.The algorithm follows the standard Monin-Obukhov similarity approach for near-surface meteorological measurements but includes separate models for the ocean's cool skin and the diurnal warm layer, which are used to derive true skin temperature from the bulk temperature measured at some depth near the surface.

To obtain bulk surface flux estimates approaching the _+10 W m -: accuracy desired for the Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (COARE) program, bulk water temperature data from ships and buoys must be corrected for cool-skin and diurnal warm-layer effects. In this paper we describe two simple scaling models to estimate these corrections. The cool-skin model is based on the standard Saunders [ 1967] treatment, including the effects of solar radiation absorption, modified to include both shear-driven and convectively driven turbulence through their relative contributions to the near-surface turbulent kinetic energy dissipation rate. Shear and convective effects are comparable at a wind speed of about 2.5 m s -•. For the R/V Moana Wave COARE data collected in the tropical western Pacific, the model gives an average cool skin of 0.30 K at night and an average local noon value of 0.18 K. The warm-layer model is based on a single-layer scaling version of a model by Price et al. [1986]. In this model, once solar heating of the ocean exceeds the combined cooling by turbulent scalar heat transfer and net longwave radiation, then the main body of the mixed layer is cut off from its source of turbulence. Thereafter, surface inputs of heat and momentum are confined to a depth Dr that is determined by the subsequent integrals of the heat and momentum. The model assumes linear profiles of temperature-induced and surface-stress-induced current in this "warm layer." The model is shown to describe the peak afternoon warming and diurnal cycle of the warming quite accurately, on average, with a choice of a critical Richardson number of 0.65. For a clear day with a 10-m wind speed of 1 rn s -•, the peak afternoon warming is about 3.8 K with a warmlayer depth of 0.7 m, decreasing to about 0.2 K and 19 rn at a wind speed of 7 m s -•. For an average over 70 days sampled during COARE, the cool skin increases the average atmospheric heat input to the ocear/by about 11 W m-:; the warm layer decreases it by about 4 W m -: (but the effect can be 50 W m -: at midday). 1. Introduction Sea surface temperature (SST) is a key variable driving air-sea interaction. SST and air-sea fluxes were a dominant component of the study of the tropical western Pacific warm pool in the Tropical Ocean-Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) held in 1992-1993 [Webster and Lukas, 1992]. Uncertainties in air-sea temperature difference represent a major uncertainty in assessing the heat balance of the warm pool [Lukas, Paper number 95JC03190. 0148-0227/96/95JC-03190505.00 1989]. Fairall et al. [1996a] have shown that to estimate this heat balance to an accuracy of 10 W m '2 requires specification of the SST to an accuracy of _+0.2 K. Bulk flux routines are based on the empirical relationship between the turbulent fluxes and the air-sea contrasts of wind, humidity, and temperature; the SST is the lower thermal boundary condition. Logically• the proper temperature is taken at the air-sea...

This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s 21 ) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient a in the COARE algorithm is modified to a 5 mU 10N 1 b, where m 5 0.017 m 21 s and b 5 20.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s 21. Wave age-and wave slope-dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed-dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed-, wave age-, and wave slopedependent formulations give similar results-the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s 21.

[1] Air-water gas transfer influences CO 2 and other climatically important trace gas fluxes on regional and global scales, yet the magnitude of the transfer is not well known. Widely used models of gas exchange rates are based on empirical relationships linked to wind speed, even though physical processes other than wind are known to play important roles. Here the first field investigations are described supporting a new mechanistic model based on surface water turbulence that predicts gas exchange for a range of aquatic and marine processes. Findings indicate that the gas transfer rate varies linearly with the turbulent dissipation rate to the 1 = 4 power in a range of systems with different types of forcing -in the coastal ocean, in a macro-tidal river estuary, in a large tidal freshwater river, and in a model (i.e., artificial) ocean. These results have important implications for understanding carbon cycling.