14th Conference on Interaction of the Sea and Atmosphere


Improved estimates of net air-sea Fluxes over the atlantic ocean

Abderrahim Bentamy, IFREMER, Plouzane, France; and H. L. Ayina, A. M. Nunez, K. Katsaros, and R. Pinker

The key surface parameters involved in the exchange of energy between the atmosphere and oceans are: wind stress, shortwave (SW) and longwave (LW) radiative fluxes, surface turbulent latent and sensible heat fluxes. These are essential to improve modeling simulations of climate variations and oceanic dynamic process studies. In this study investigated are flux components over the Atlantic tropical ocean using estimates derived at six institutes. The surface wind including wind stress, latent and sensible heat fluxes are primarily estimated from satellite observations and provided by: the Institut Français pour l'Exploitation de la MER (IFREMER_1); the Hamburg Ocean Atmosphere Parameters and Fluxes (HOAPS_2) satellite group; and by the Goddard Satellite-based Surface Turbulent Fluxes group (GSSTF_2). The surface meteorological variables and turbulent heat fluxes retrieved from the European Centre for Medium-Range Weather Forcasts (ECMWF operational analyses), from ECMWF reanalysis (ERA40), and from the National Centers for Environmental Prediction (NCEP 1 and 2 reanalyses). The methodology for obtaining fluxes from satellite observations uses physical properties of radar and radiometer measurements, empirical and inverse models relating satellite observations and surface parameters, and objective analysis merging various satellite estimates. A high-resolution dataset is prepared for the Atlantic Ocean, with a spatial resolution between 0.5° and 1°, and temporal resolution between one day and one week. The satellite data come from the European Remote Sensing satellite scatterometer (ERS-2), NASA scatterometer Seawinds onboard QuikScat, and several defense Meteorological Satellite Program (DMSP) radiometers (Special Sensor Microwave/Imager [SSM/I] F10 – F15), Meteosat, and GOES. The six flux sources are compared with high quality moored buoy observations (PIRATA network). The buoy wind stresses, latent heat and sensible heat fluxes are determined from in-situ measurements based on the latest version of Coupled-Atmosphere Response Experiment (COARE) flux model. The comparison analysis indicates that in general the remotely sensed fluxes are underestimated with respect to the buoy observations, while numerical model data overestimate the fluxes. For instance the difference bias of IFREMER and ECMWF latent heat flux is about 7 W/m² and -33 W/m² respectively. The corresponding rms values are about 29 W/m² and 40 W/m². Depending upon the region, season, and flux source, the statistical parameters characterizing the differences between buoy, satellite and numerical flux estimates, vary significantly. They are related to the bulk parameterization used to estimate the fluxes, and the bias in surface variables. To enhance the comparison between satellite estimates (IFREMER) and buoy observations, a method to estimate air temperature has been developed and tested. The latter is then used with the retrieved satellite winds, specific air humidity, specific surface humidity, and sea surface temperature to recalculate the fluxes. Significant improvement in the agreement between buoy and IFREMER flux estimates is achieved. To assess the quality of satellite fluxes, several simulations were performed with an oceanic global circulation model (ORCA) using remotely sensed and numerical model flux estimated as forcing functions. The annual mean ORCA response to both surface fluxes is investigated in terms of mean and variability of sea surface temperature. .

Session 6, Space–Based Air–Sea Turbulent Fluxes
Tuesday, 31 January 2006, 1:45 PM-3:00 PM, A309

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