The current status of meteorological sensors used aboard ships and buoys to measure the air-sea fluxes of momentum, heat, and freshwater is reviewed. Methods of flux measurement by the bulk aerodynamic, inertial dissipation and eddy-correlation methods are considered; and areas are identified where improvements are needed in measurement of the basic variables. In some cases, what is required is the transition from emergent to operational technology, in others new technologies are needed. Uncertainties in measured winds caused by flow distortion over the ship are discussed; and the possible role of computational fluid mechanics models to obtain corrections is considered. Basic studies are also needed on the influence of waves and rain on the fluxes. The issues involved in the specification of sea surface temperature are described, and the relative merits of the available sensors are discussed. The improved capability of buoy-mounted systems will depend on the emergence of low-power instruments, and/or new means of increasing the available power capacity. Other issues covered include the continuing uncertainty about the performance of rain gauges and short-wave radiometers. Also, the requirements for new instruments to extend the range of observations to extreme wind conditions are outlined, and the latest developments in the measurement of aerosol fluxes by eddy-correlation are presented.

The current status of meteorological sensors used aboard ships and buoys to measure the air-sea fluxes of momentum. heat. and freshwater is reviewed. Methods of flux measurement by the bulk aerodynamic. inertial dissipation and eddy-correlation methods are considered: and areas are identified where improvements are needed in measurement of the basic variables. In some cases. what is required is the transition from emergent to operational technology, in others new technologies are needed. Uncertainties in measured winds caused by flow distortion over the ship are discussed; and the possible role of computational fluid mechanics models to obtain corrections is considered. Basic studies arc also needed on the influence of waves and rain on the fluxes. The issues involved in the specification of sea surface temperature are described. and the relative merits of the available sensors are discussed. The improved capability of buoy-mounted systems will depend on the emergence of low-power Instruments, and/or new means of increasing the available power capacity. Other issues covered include the continuing uncertainty about the performance of rain gauges and short-wave radiometers. Also, the requirements for new instruments to extend the range of observations to extreme wind conditions are outlined, and the latest developments in the measurement of aerosol fluxes by eddy-correlation are presented.

High-resolution surface fluxes over the global ocean are needed to evaluate coupled atmosphere–ocean models and weather forecasting models, provide surface forcing for ocean models, understand the regional and temporal variations of the exchange of heat between the atmosphere and ocean, and provide a large-scale context for field experiments. Under the auspices of the World Climate Research Programme (WCRP) Global Energy and Water Cycle Experiment (GEWEX) Radiation Panel, the SEAFLUX Project has been initiated to investigate producing a high-resolution satellite-based dataset of surface turbulent fluxes over the global oceans to complement the existing products for surface radiation fluxes and precipitation. The SEAFLUX Project includes the following elements: a library of in situ data, with collocated satellite data to be used in the evaluation and improvement of global flux products; organized intercomparison projects, to evaluate and improve bulk flux models and determination from the satellite of the input parameters; and coordinated evaluation of the flux products in the context of applications, such as forcing ocean models and evaluation of coupled atmosphere–ocean models. The objective of this paper is to present an overview of the status of global ocean surface flux products, the methodology being used by SEAFLUX, and the prospects for improvement of satellite-derived flux products.

In 1996, version 2.5 of the Coupled Ocean-Atmosphere Response Experiment (COARE) bulk algorithm was published, and it has become one of the most frequently used algorithms in the air-sea interaction community. This paper describes steps taken to improve the algorithm in several ways. The number of iterations to solve for stability has been shortened from 20 to 3, and adjustments have been made to the basic profile stability functions. The scalar transfer coefficients have been redefined in terms of the mixing ratio, which is the fundamentally conserved quantity, rather than the measured water vapor mass concentration. Both the velocity and scalar roughness lengths have been changed. For the velocity roughness, the original fixed value of the Charnock parameter has been replaced by one that increases with wind speeds of between 10 and 18 m s(-1). The scalar roughness length parameterization has been simplified to fit both an early set of NOAA/Environmental Technology Laboratory (ETL) experiments and the Humidity Exchange Over the Sea (HEXOS) program. These changes slightly increase the fluxes for wind speeds exceeding 10 m s(-)1. For interested users, two simple parameterizations of the surface gravity wave influence on fluxes have been added (but not evaluated).This new version of the algorithm (COARE 3.0) was based on published results and 2777 1-h covariance flux measurements in the ETL inventory. To test it, 4439 new values from field experiments between 1997 and 1999 were added, which now dominate the database, especially in the wind speed regime beyond 10 m s(-1), where the number of observations increased from 67 to about 800. After applying various quality controls, the database was used to evaluate the algorithm in several ways. For an overall mean, the algorithm agrees with the data to within a few percent for stress and latent heat flux. The agreement is also excellent when the bulk and directly measured fluxes are averaged in bins of 10-m neutral wind speed. For a more stringent test, the average 10-m neutral transfer coefficients were computed for stress and moisture in wind speed bins, using different averaging schemes with fairly similar results. The average (mean and median) model results agreed with the measurements to within about 5% for moisture from 0 to 20 m s(-1). For stress, the covariance measurements were about 10% higher than the model at wind speeds over 15 m s(-1), while inertial-dissipation measurements agreed closely at all wind speeds. The values for stress are between 8% (for inertial dissipation) and 18% (for covariance) higher at 20 m s(-1) than two other classic results. Twenty years ago, bulk flux schemes were considered to be uncertain by about 30%; the authors find COARE 3.0 to be accurate within 5% for wind speeds of 0-10 m s(-1) and 10% for wind speeds of between 10 and 20 m s(-1).

The methods and initial results of an extensive pilot study, the Joint Air–Sea Monsoon Interaction Experiment (JASMINE) held in the Indian Ocean during the summer of 1999, are described. The experimental design was based on the precept that the monsoon sways back and forth from active to inactive (or break) phases and that these intraseasonal oscillations are coupled ocean–atmosphere phenomena that are important components of the monsoon system. JASMINE is the first comprehensive study of the coupled ocean–atmosphere system in the eastern Indian Ocean and the southern Bay of Bengal. Two research vessels, the NOAA ship Ronald H. Brown and the Australian research vessel Franklin, totaled 52 days of surveillance in April–June and September, with 388 conductivity–temperature–depth (CTD) casts and 272 radiosonde ascents. In addition, both ships carried identical flux systems to measure the ocean–atmosphere interaction. The Brown had five radar systems and profilers, including a cloud radar and a Doppler C-band...

Comparisons of mean ambient temperature, specific humidity, static pressure, and horizontal wind from the five Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) boundary layer aircraft were obtained from 38 two- and three-aircraft, close-formation, level runs. These, together with consideration of surface measurements from buoys and ships, led to proposed empirical corrections for the aircrafts temperature, humidity, and pressure measurements, minimizing the systematic errors between the aircraft data sets. The aircraft-measured winds were also compared. The TOGA COARE bulk flux algorithm was used to extrapolate the low-level aircraft data to the individual ship and buoy sensor heights for 267 overflight comparisons. In addition, all low-level aircraft data and corresponding ship and buoy data from boundary layer missions were extracted and adjusted to a 10-m reference height. The recommended aircraft corrections bring the aircraft-ship-buoy data sets into better agreement, resulting in a consistent data set for air-sea interaction analyses. Frequency distributions of the 10-m aircraft, ship, and buoy data from the boundary layer missions also agree.

This paper examines the interpolation betweenBusinger–Dyer (Kansas-type) formulae,ϕu = (1 -1 6ζ )-1/4 andϕt = (1 - 16ζ )-1/2, and free convection forms. Based on matching constraints, the constants, au and at, in the convective flux-gradient relations, ϕu = (1 - auζ )-1/3 and ϕt = (1 - atζ )-1/3, are determined. It isshown that au and at cannot be completely independent if convective forms are blended with theKansas formulae. In other words, these relationships already carryinformation about au and at. This follows because the Kansas relations cover a wide stability range (up to ζ = - 2), which includes a lower part of the convective sublayer (about 0.1 < - ζ < 2). Thus, there is a subrange where both Kansas and convective formulae are valid. Matching Kansas formulae and free convection relations within thesubrange 0.1 < -ζ < 2 and independently smoothing ofthe blending function are used to determine au and at. The values au = 10 for velocity and at = 34for scalars (temperature and humidity) give a good fit. This new approacheliminates the need for additional independent model constants and yields a`smooth' blending between Kansas and free-convection profileforms in the COARE bulk algorithm.

R/V Franklin followed a drifter for 8 days in the equatorial Indian Ocean to test the accuracy of mixed‐layer heat and freshwater budget closure. Four‐hourly triangles were repeated, towing a SeaSoar with a photometer and conductivity‐temperature‐depth (CTD) profiler. Currents relative to the buoy at one depth were obtained from (a) a current meter at 25 m below the buoy; (b) a Global Positioning System estimate; (c) a drag estimate. Acoustic Doppler current profiler (ADCP) shears provided currents at other depths, (b) and (c) agreed closely but differed from (a), possibly due to severe conditions at the current meter. Vertical advection was estimated from ADCP divergence around each triangle. Measurements on the buoy and the ship, calibrated earlier in the Coupled Ocean‐Atmosphere Response Experiment (COARE), provided bulk surface fluxes. Accuracy of net surface heat fluxes was estimated at ±10 W/m 2 . Rainfall differed considerably between the buoy and ship, but other quantities including shortwave radiation were very similar, even on cloudy days. A formalism for the budgets above a given isopycnal is developed, to clearly distinguish horizontal and vertical advection. When (b) and (c) above were used with the best estimate of surface fluxes, the 8‐day heat budget misclose for water above the 21.5 isopycnal was (−4.6±5) W/m 2 ; the diurnal heating cycle was well resolved. The freshwater budget misclose was (0.9±3.5) mm/d. A small amount of vertical diffusion, in the ratio determined by the slope of the T‐S curve, will reduce both misclosures. Cruise design considerations for minimizing errors in the advection and storage components of heat and freshwater budgets are discussed.

The calibration and accuracy of the Eppley precision infrared radiometer (PIR) is examined both theoretically and experimentally. A rederivation of the fundamental energy balance of the PIR indicates that the calibration equation in common use in the geophysical community today contains an erroneous factor of the emissivity of the thermopile. If a realistic value (0.98) for the emissivity is' used, then this leads to errors in the total flux of 5-10 W m(-2). The basic precision of the instrument is found to be about 1.5% of the total IR irradiance when the thermopile voltage and both dome and case temperatures are measured. If the manufacturer's optional battery-compensated output is used exclusively, then the uncertainties increase to about 1.5% of the total (20 W m(-2)). It is suggested that a modern radiative transfer model combined with radiosonde profiles can be used as a secondary standard to improve the absolute accuracy of PIR data from field programs. Downwelling IR fluxes calculated using the Rapid Radiative Transfer Model (RRTM), from 55 radiosondes ascents in cloud-free conditions during the Tropical Oceans Global Atmosphere Coupled Ocean-Atmosphere Response Experiment field program, gave mean agreement within 2 W m(-2) of those measured with a shipborne PIR. PIR data from two sets of instrument intercomparisons were used to demonstrate ways of detecting inconsistencies in thermopile-sensitivity coefficients and dome-heating correction coefficients. These comparisons indicated that pairs of PIRs are easily corrected to yield mean differences of 1 W m(-2) and rms differences of 2 W m(-2). Data from a previous field program over the ocean indicate that pairs of PIRs can be used to deduce the true surface skin temperature to an accuracy of a few tenths of a kelvin.

Satellite sea surface skin temperature (SSST) mips are readily available from precisely calibrated radiometer systems such as the ERS along-track scanning radiometer and, in the near future, from the moderate-resolution imaging spectroradiometer. However, the use of su,surface bulk sea surface temperature (BSST) measurements as the primary source of in situ data required for the development of new sea surface temperature algorithms and the accurate validation of these global datasets is questionable. This is because BSST measurements are not a measure of the sea surface skin temperature, which is actually observed by a satellite infrared radiometer. Consequently, the use of BSST data for validation :Ind derivation of satellite derived "pseudo-BSST" and SSST datasets will limit their accuracy to at least the rms deviation of the BSST-SSST difference, typically about +/-0.5 K. Unfortunately, the prohibitive cost and difficulty of deploying infrared radiometers at sea has prevented the regular collection of a comprehensive global satellite SSST validation dataset. In response to this situation, an assessment of the TASCO THI-500L infrared radiometer system as a potential candidate for the widespread validation of satellite SSST observations is presented. This is a low-cost, broadband radiometer that has been commonly deployed in the field to measure SSST by several research groups. A comparison between SSST derived from TASCO THI-500L measurements anl contemporaneous scanning infrared sea surface temperature radiometer measurements, which are accurate to better than 0.1 K, demonstrates low bias (0.1 K) and rms (0.08 K) differences between the two instruments. However, to achieve this accuracy, the TASCO THI-500L radiometer must be deployed with care to ensure that the radiometer fore-optics are kept free of salt water contamination and shaded from direct sunlight. When this is done, this type of low-cost radiometer system could form the core of a global SSST validation program.

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. The basic structure is an outgrowth of the Liu‐Katsaros‐Businger [Liu et al., 1979] method, with modifications to include a different specification of the roughness/stress relationship, a gustiness velocity to account for the additional flux induced by boundary layer scale variability, and profile functions obeying the convective limit. Additionally, we have considered the contributions of the sensible heat carried by precipitation and the requirement that the net dry mass flux be zero (the so‐called Webb correction [Webb et al., 1980]). The algorithm has been tuned to fit measurements made on the R/V Moana Wave in the three different cruise legs made during the Coupled Ocean‐Atmosphere Response Experiment. These measurements yielded 1622 fifty‐min averages of fluxes and bulk variables in the wind speed range from 0.5 to 10 m s−1. The analysis gives statistically reliable values for the Charnock [1955] constant (α = 0.011) and the gustiness parameter (β = 1.25). An overall mean value for the latent heat flux, neutral bulk‐transfer coefficient was 1.11 × 10−3, declining slightly with increasing wind speed. Mean values for the sensible and latent heat fluxes were 9.1 and 103.5 W m−2; mean values for the Webb and rain heat fluxes were 2.5 and 4.5 W m−2. Accounting for all factors, the net surface heat transfer to the ocean was 17.9 ± 10 W m−2.

To obtain bulk surface flux estimates approaching the ±10 W m−2 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−1. 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 DT 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 m s−1, the peak afternoon warming is about 3.8 K with a warm‐layer depth of 0.7 m, decreasing to about 0.2 K and 19 m at a wind speed of 7 m s−1. For an average over 70 days sampled during COARE, the cool skin increases the average atmospheric heat input to the ocean by about 11 W m−2; the warm layer decreases it by about 4 W m−2 (but the effect can be 50 W m−2 at midday).