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R. C. LANE and R. A. WELLS

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W. C. HAINES and R. A. WELLS

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R. A. Weller and S. P. Anderson

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A major goal of the Coupled Ocean-Atmosphere Response Experiment (COARE) was to achieve significantly more accurate and complete descriptions of the surface meteorology and air-sea fluxes in the western equatorial warm pool region. Time series of near-surface meteorology from a buoy moored near the center of the COARE Intensive Flux Array (IFA) are described here. The accuracies of the measurements and the derived fluxes are quantified; agreement between average net heat fluxes at the buoy and two nearby research ships is better than 10 W m−2 during three intercomparisons. Variability in the surface meteorology and fluxes associated with westerly wind bursts, periods of low winds, and short-lived, deep convective events characteristic of the region was large compared to the 4-month means. The ECMWF (European Centre for Medium-Range Weather Forecasts) analysis and prediction fields differed most from the buoy data during periods of short-lived, deep convective events, when several day averages of the net heat flux differed by more than 70 W m−2 and had the opposite sign. A one-dimensional ocean model run to examine the sensitivity of the upper-ocean response to differences between the observed and the ECMWF fluxes illustrates the importance of the short-lived events as well as of the wind bursts in maintaining the temperature of the warm pool.

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M. A. MacWhorter and R. A. Weller

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Errors in shortwave solar radiation measurements resulting from mean tils and rocking motions, as well as from the response time of the sensors, are determined experimentally. The magnitude of the mean tilt error can be large and lead to errors in daily-averaged incoming shortwave radiation in excess of 10 W m−2. Mean errors due to rocking motions and time response errors are less severe. The spatial distribution of the diffuse component of the radiation and the motion of the platform must both be known to attempt to correct for this error. An algorithm to perform this correction was derived, yet is only sufficiently accurate when the time response of the pyranometer is significantly smaller than the period of the rocking motion. Gimballing the sensors may be a more practical method of error reduction.

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K. A. Moyer and R. A. Weller

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Reliable estimates of the exchange of heat, moisture, and momentum across the air–sea interface are essential in assessing the local “representativeness” of the surface forcing fields depicted by global model and climatological datasets. The reliability and extended length of the in situ data collected by a large-scale array of buoys deployed during the Subduction Experiment make this dataset particularly well suited to providing such an assessment. The Subduction Experiment was designed to explore the process by which the mixed layer waters of the eastern subtropical North Atlantic are incorporated into the top of the main thermocline. To this end, an array of five buoys was maintained between 18°–33°N and 22°–34°W from June 1991 to June 1993. In situ dynamic, thermodynamic, and radiometric measurements are utilized along with a state-of-the-art bulk flux algorithm to estimate the time-dependent surface forcing at each of the buoys. The resulting air–sea fluxes are compared to similar quantities offered by the Isemer and Hasse (Bunker) and the Wright–Oberhuber Comprehensive Ocean–Atmosphere Data Set climatological datasets, and global model forecasts from the European Centre for Medium-Range Weather Forecasts and the National Centers for Environmental Prediction.

Some substantial differences are exhibited between the surface forcing components garnered from the Subduction Experiment buoys and those of the climatological and model products. The mean net heat flux from the Subduction Experiment buoys exhibits a qualitatively similar spatial gradient to that of the climatological and model products across the array, but generally reflects a greater oceanic heat gain in summer and a smaller oceanic heat loss in winter. On shorter timescales, the models’ inability to replicate the heat and radiometric fluxes of the buoys is reflected in large mean standard deviations of the differences between the buoy and model fluxes at 6-h intervals. Some of the observed differences are attributed to differences in bulk formulas and/or differences in the mean variables from which the bulk air–sea fluxes are derived, while others are simply an artifact of the spatial and temporal filtering inherent within the climatological and model products.

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T. P. Barnett, R. A. Knox, and R. A. Weller

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During January and February 1974 the NORPAX POLE experiment was carried out in the central Pacific to begin collection of data needed to design a large-scale ocean/atmosphere monitoring program. This paper describe features of the ocean temperature field observed during POLE within a region of about 400 km in diameter centered near 35°N, 155°W. The temperature field, which was approximately stationary during the month-long experiment, was dominated by a strong north-south gradient as expected. The east-west gradient was negligible. Superimposed on this mean field was energetic noise with typical rms isotherm displacements of 25 m near the bottom of the mixed layer. The characteristic horizontal scale of this noise was 50 km near the surface although the field appeared to be anisotropic. The energy, scale length and degree of anisotropy all decrease with depth. The implications of these observations to a sampling strategy are discussed as are other conclusions drawn from a statistical analysis of the temperature data.

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Philip R. Thompson, Mark A. Merrifield, Judith R. Wells, and Chantel M. Chang

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The rate of coastal sea level change in the northeast Pacific (NEP) has decreased in recent decades. The relative contributions to the decreased rate from remote equatorial wind stress, local longshore wind stress, and local windstress curl are examined. Regressions of sea level onto wind stress time series and comparisons between NEP and Fremantle sea levels suggest that the decreased rate in the NEP is primarily due to oceanic adjustment to strengthened trade winds along the equatorial and coastal waveguides. When taking care to account for correlations between the various wind stress time series, the roles of longshore wind stress and local windstress curl are found to be of minor importance in comparison to equatorial forcing. The predictability of decadal sea level change rates along the NEP coastline is therefore largely determined by tropical variability. In addition, the importance of accounting for regional, wind-driven sea level variations when attempting to calculate accelerations in the long-term rate of sea level rise is demonstrated.

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Robert A. Weller, Daniel L. Rudnick, Nancy J. Pennington, Richard P. Trask, and James R. Valdes

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Measurements of upper ocean variability were made in the subtropical convergence zone southwest of Bermuda from an array of five surface moorings set with spacings of 16 to 53 km. The intent was to observe oceanic fronts and to quantify the spatial gradients associated with them. Vector Measuring Current Meters (VMCMS) and Vector Averaging Current Meters (VACMS) were attached to the mooring lines beneath the surface buoys to measure velocities and temperatures. Modifications were made to the VMCMs in an attempt to improve data return. The performance and accuracy of these moored instruments are examined. Predeployment and postdeployment calibrations were carried out; and other sources of error, such as mooring motion, are considered. A number of oceanic fronts passed through the moored array during the experiment, and the horizontal gradients observed in the velocity and temperature fields were significantly larger than the uncertainties in measuring those gradients.

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T. D. Dickey, D. V. Manov, R. A. Weller, and D. A. Siegel

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A theory for pyrgeometer operation is utilized for determining downwelling longwave radiation. Errors in downwelling longwave radiation measurements are due to differences in pyrgeometer body and dome temperatures compared to that of the atmosphere. Additionally, incident shortwave radiation fluxes may be important. Using the present theory along with laboratory and field observations, it appears that downwelling longwave heat fluxes can be measured with errors less than 6 W m−2. Longwave heat flux observations from surface buoys deployed in four different oceanic regions suggest that 1) incoming longwave measurements from buoys are repeatable, 2) uncertainties in radiometer calibration are significant and systematic, and 3) pyrgeometers are affected by direct and indirect solar heating. A hybrid measurement method for the determination of net longwave heat flux at the air-sea interface is described. The authors recommend improvement in calibration procedures as well as development of a radiometer to be used as a transfer standard to compare with in situ measurements. Uncertainties in sea surface skin temperature and emissivity are contributors to the error in the net longwave heat flux. However, a targeted error limit goal of ±10 W m−2 for the monthly mean net longwave heat flux appears to be achievable.

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R.A. Weller, M.A. Donelan, M.G. Briscoe, and N.E. Huang

This paper gives a general overview of two ocean wave experiments. The experimental goals of the Surface Wave Processes Program (SWAPP) and of the Surface Wave Dynamics Experiment (SWADE) are quite different but complementary. In general terms, SWAPP is focused on local processes: principally wave breaking, upper mixed layer dynamics, and microwave and acoustic signatures of wave breaking. SWADE, on the other hand, is concerned primarily with the evolution of the directional wave spectrum in both time and space, improved understanding of wind forcing and wave dissipation, the effect of waves on the air-sea coupling mechanisms, and the radar response of the surface. Both programs acknowledge that wave dissipation is the weakest link in our understanding of wave evolution on the ocean. SWAPP takes a closer look at wave dissipation processes directly, while SWADE, with the use of fully non-linear (third generation) wave models and carefully measured wind forcing, provides an opportunity to study the effect of dissipation on spectral evolution. Both programs involve many research platforms festooned with instruments and large teams of scientists and engineers gathering and analyzing huge datasets. The success of SWAPP and SWADE will be measured in the degree to which the results can be integrated into a far more complete picture than we have had heretofore of interfacial physics, wave evolution, and mixed layer dynamics.

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