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D. Bourras, H. Branger, G. Reverdin, L. Marié, R. Cambra, L. Baggio, C. Caudoux, G. Caudal, S. Morisset, N. Geyskens, A. Weill, and D. Hauser

Abstract

The present paper describes a new type of floating platform that was specifically designed for estimating air–sea fluxes, investigating turbulence characteristics in the atmospheric surface boundary layer, and studying wind–wave interactions. With its design, it can be deployed in the open ocean or in shallow-water areas. The system is designed to be used from a research vessel. It can operate for ~10 h as a drifting wave rider and 3 h under power. Turbulence and meteorological instrument packages are placed at a low altitude (1–1.5 m). It was deployed for validation purposes during the Front de Marée, Variabilité (FROMVAR), 2011 experiment off the west coast of Brittany, France. Wind friction velocity and surface turbulent buoyancy flux were estimated using eddy covariance, spectral, bulk, and profile methods. The comparisons of the four methods show a reasonable agreement except for the spectral buoyancy flux. This suggests that the platform design is correct. Also, the wind measured at a fixed height above the sea shows spectral coherence with wave heights, such that wind and swell are in phase, with the largest wind values on top of swell crests. This result in qualitative agreement with current model predictions supports the capability of the Ocean Coupled to Atmosphere, Research at the Interface with a Novel Autonomous platform (OCARINA) to investigate wind–swell interactions.

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A. Weill, L. Eymard, G. Caniaux, D. Hauser, S. Planton, H. Dupuis, A. Brut, C. Guerin, P. Nacass, A. Butet, S. Cloché, R. Pedreros, P. Durand, D. Bourras, H. Giordani, G. Lachaud, and G. Bouhours

Abstract

An accurate determination of turbulent exchanges between the ocean and the atmosphere is a prerequisite to identify and assess the mechanisms of interaction that control part of the variability in the two media over a wide range of spatial and temporal scales. An extended dataset for estimating air–sea fluxes (representing nearly 5700 h of turbulence measurements) has been collected since 1992 during six dedicated experiments performed in the Atlantic Ocean and the Mediterranean Sea. This paper presents the methodology used through the successive experiments to progress in this field. The major developments concern (i) flux instrumentation, with the deployment of a microwave refractometer to get the latent heat flux in most meteorological conditions; (ii) the analysis of airflow distortion effects around the ship structure and sensors through both computational fluid dynamics and physical simulations in a water tank, then the derivation of correction for these effects; (iii) the application of both inertial dissipation and eddy-correlation methods from the various experiments, allowing the authors to assess and discuss flux-determination methods on ships, and particularly bulk parameterization; (iv) the validation and analysis of mesoscale surface flux fields from models and satellites by using ship data, showing some deficiencies in operational model fields from ECMWF, the need of high-quality fluxes to interpret ocean–atmosphere exchanges, and the potential advantage of satellite retrieval methods. Further analysis of these datasets is being performed in a unique database (the ALBATROS project, open to the international scientific community). It will include refinement of airflow distortion correction and reprocessing of earlier datasets, the investigation of fluxes under specific conditions (low wind), and the effect of sea state among others. It will also contribute to further validation and improvements of satellite retrievals in various climatic/meteorological conditions.

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J. A. Curry, A. Bentamy, M. A. Bourassa, D. Bourras, E. F. Bradley, M. Brunke, S. Castro, S. H. Chou, C. A. Clayson, W. J. Emery, L. Eymard, C. W. Fairall, M. Kubota, B. Lin, W. Perrie, R. A. Reeder, I. A. Renfrew, W. B. Rossow, J. Schulz, S. R. Smith, P. J. Webster, G. A. Wick, and X. Zeng

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.

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J. Vialard, J. P. Duvel, M. J. McPhaden, P. Bouruet-Aubertot, B. Ward, E. Key, D. Bourras, R. Weller, P. Minnett, A. Weill, C. Cassou, L. Eymard, T. Fristedt, C. Basdevant, Y. Dandonneau, O. Duteil, T. Izumo, C. de Boyer Montégut, S. Masson, F. Marsac, C. Menkes, and S. Kennan

The Vasco-Cirene program explores how strong air-sea interactions promoted by the shallow thermocline and high sea surface temperature in the Seychelles-Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceanographic cruise collected oceanic, atmospheric, and air-sea flux observations in this region in January–February 2007. The contemporaneous Vasco field experiment complemented these measurements with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a mooring and 12 Argo profilers.

Unusual conditions prevailed in the Indian Ocean during January and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles-Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cooling over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.

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J. Vialard, J. P. Duvel, M. J. Mcphaden, P. Bouruet-Aubertot, B. Ward, E. Key, D. Bourras, R. Weller, P. Minnett, A. Weill, C. Cassou, L. Eymard, T. Fristedt, C. Basdevant, Y. Dandonneau, O. Duteil, T. Izumo, C. de Boyer Montégut, S. Masson, F. Marsac, C. Menkes, and S. Kennan

Abstract

The Vasco—Cirene field experiment, in January—February 2007, targeted the Seychelles—Chagos thermocline ridge (SCTR) region, with the main purpose of investigating Madden—Julian Oscillation (MJO)-related SST events. The Validation of the Aeroclipper System under Convective Occurrences (Vasco) experiment (Duvel et al. 2009) and Cirene cruise were designed to provide complementary views of air—sea interaction in the SCTR region. While meteorological balloons were deployed from the Seychelles as a part of Vasco, the Research Vessel (R/V) Suroît was cruising the SCTR region as a part of Cirene.

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