Improved near real time surface wind resolution over the Mediterranean Sea

International audienceSeveral scientific programs, including the Mediterranean Forecasting System Toward Environmental Predictions (MFSTEP project), request high space and time resolutions of surface wind speed and direction. The purpose of this paper is to focus on surface wind improvements over the global Mediterranean Sea, based on the blending near real time remotely sensed wind observations and ECMWF wind analysis. Ocean surface wind observations are retrieved from QuikSCAT scatterometer and from SSM/I radiometers available at near real time at Météo-France. Using synchronous satellite data, the number of remotely sensed data available for each analysis epoch (00:00 h; 06:00 h; 12:00 h; 18:00 h) is not uniformly distributed as a function of space and time. On average two satellite wind observations are available for each analysis time period. The analysis is performed by optimum interpolation (OI) based on the kriging approach. The needed covariance matrixes are estimated from the satellite wind speed, zonal and meridional component observations. The quality of the 6-hourly resulting blended wind fields on 0.25° grid are investigated trough comparisons with the remotely sensed observations as well as with moored buoy wind averaged wind estimates. The blended wind data and remotely wind observations, occurring within 3 h and 0.25° from the analysis estimates, compare well over the global basin as well as over the sub-basins. The correlation coefficients exceed 0.95 while the rms difference values are less than 0.30 m/s. Using measurements from moored buoys, the high-resolution wind fields are found to have similar accuracy as satellite wind retrievals. Blended wind estimates exhibit better comparisons with buoy moored in open sea than near shore

Improved near real time surface wind resolution over the Mediterranean Sea

International audienceSeveral scientific programs, including the Mediterranean Forecasting System Toward Environmental Predictions (MFSTEP project), request high space and time resolutions of surface wind speed and direction. The purpose of this paper is to focus on surface wind improvements over the global Mediterranean Sea, based on the blending near real time remotely sensed wind observations and ECMWF wind analysis. Ocean surface wind observations are retrieved from QuikSCAT scatterometer and from SSM/I radiometers available at near real time at Météo-France. Using synchronous satellite data, the number of remotely sensed data available for each analysis epoch (00:00 h; 06:00 h; 12:00 h; 18:00 h) is not uniformly distributed as a function of space and time. On average two satellite wind observations are available for each analysis time period. The analysis is performed by optimum interpolation (OI) based on the kriging approach. The needed covariance matrixes are estimated from the satellite wind speed, zonal and meridional component observations. The quality of the 6-hourly resulting blended wind fields on 0.25° grid are investigated trough comparisons with the remotely sensed observations as well as with moored buoy wind averaged wind estimates. The blended wind data and remotely wind observations, occurring within 3 h and 0.25° from the analysis estimates, compare well over the global basin as well as over the sub-basins. The correlation coefficients exceed 0.95 while the rms difference values are less than 0.30 m/s. Using measurements from moored buoys, the high-resolution wind fields are found to have similar accuracy as satellite wind retrievals. Blended wind estimates exhibit better comparisons with buoy moored in open sea than near shore

Evaluation of high-resolution surface wind products at global and regional scales

High resolution surface wind fields covering the global ocean, estimated from remotely sensed wind data and ECMWF wind analyses, have been available since 2005 with a spatial resolution of 0.25 degrees in longitude and latitude, and a temporal resolution of 6h. Their quality is investigated through various comparisons with surface wind vectors from 190 buoys moored in various oceanic basins, from research vessels and from QuikSCAT scatterometer data taken during 2005-2006. The NCEP/NCAR and NCDC blended wind products are also considered. The comparisons performed during January-December 2005 show that speeds and directions compare well to in-situ observations, including from moored buoys and ships, as well as to the remotely sensed data. The root-mean-squared differences of the wind speed and direction for the new blended wind data are lower than 2m/s and 30 degrees, respectively. These values are similar to those estimated in the comparisons of hourly buoy measurements and QuickSCAT near real time retrievals. At global scale, it is found that the new products compare well with the wind speed and wind vector components observed by QuikSCAT. No significant dependencies on the QuikSCAT wind speed or on the oceanic region considered are evident.Evaluation of high-resolution surface wind products at global and regional scale

Precise measurements of the total concentration of atmospheric CO2 and (CO2)-C-13/(CO2)-C-12 isotopic ratio using a lead-salt laser diode spectrometer

International audienc

A Shared Noncapsular Antigen Is Responsible for False-Positive Reactions by Staphylococcus epidermidis in Commercial Agglutination Tests for Staphylococcus aureus

Many of the commercial slide agglutination tests for Staphylococcus aureus incorporate antibodies against cell surface antigens associated with methicillin resistance, including capsular polysaccharides and an uncharacterized antigen, serotype 18. These tests are more sensitive than the first-generation agglutination procedures that detected only bound coagulase and protein A, but they suffer from false-positive reactions with some coagulase-negative staphylococci. The aim of this study was to elucidate the mechanism for false-positive agglutination by S. epidermidis in these tests. A group of methicillin-resistant S. aureus (MRSA) isolates, including a serotype 18 strain, that were not detectable in the first-generation tests were found to be of capsular polysaccharide type 8. All of these isolates were deficient in bound coagulase and/or protein A, and they possessed a heat-stable, proteinaceous antigen that was absent from a prototype capsule type 8 strain. Enzyme-linked immunosorbent assay and agarose gel immunodiffusion experiments demonstrated that this proteinaceous antigen was also present on both methicillin-sensitive and methicillin-resistant S. epidermidis clinical isolates. S. epidermidis strains that gave false-positive agglutination test results had a considerably higher level of this antigen than strains that gave the correct negative result. These findings reveal the importance of the careful selection of MRSA strains for raising anti-capsular type 8 antibodies for use in agglutination tests. Strains devoid of the antigen shared with S. epidermidis should be used to eliminate potential cross-reactions with this coagulase-negative coccus