15 research outputs found
Recommended from our members
Review and assessment of latent and sensible heat flux accuracy over the global oceans
For over a decade, several research groups have been developing air-sea heat flux information over the global ocean, including latent (LHF) and sensible (SHF) heat fluxes over the global ocean. This paper aims to provide new insight into the quality and error characteristics of turbulent heat flux estimates at various spatial and temporal scales (from daily upwards). The study is performed within the European Space Agency (ESA) Ocean Heat Flux (OHF) project. One of the main objectives of the OHF project is to meet the recommendations and requirements expressed by various international programs such as the World Research Climate Program (WCRP) and Climate and Ocean Variability, Predictability, and Change (CLIVAR), recognizing the need for better characterization of existing flux errors with respect to the input bulk variables (e.g. surface wind, air and sea surface temperatures, air and surface specific humidities), and to the atmospheric and oceanic conditions (e.g. wind conditions and sea state). The analysis is based on the use of daily averaged LHF and SHF and the asso- ciated bulk variables derived from major satellite-based and atmospheric reanalysis products. Inter-comparisons of heat flux products indicate that all of them exhibit similar space and time patterns. However, they also reveal significant differences in magnitude in some specific regions such as the western ocean boundaries during the Northern Hemisphere winter season, and the high southern latitudes. The differences tend to be closely related to large differences in surface wind speed and/or specific air humidity (for LHF) and to air and sea temperature differences (for SHF). Further quality investigations are performed through comprehensive comparisons with daily-averaged LHF and SHF estimated from moorings. The resulting statistics are used to assess the error of each OHF product. Consideration of error correlation between products and observations (e.g., by their assimilation) is also given. This reveals generally high noise variance in all products and a weak signal in common with in situ observations, with some products only slightly better than others. The OHF LHF and SHF products, and their associated error characteristics, are used to compute daily OHF multiproduct-ensemble (OHF/MPE) estimates of LHF and SHF over the ice-free global ocean on a 0.25° × 0.25° grid. The accuracy of this heat multiproduct, determined from comparisons with mooring data, is greater than for any individual product. It is used as a reference for the anomaly characterization of each individual OHF product
Optimum satellite remote sensing of the marine carbonate system using empirical algorithms in the global ocean, the Greater Caribbean, the Amazon Plume and the Bay of Bengal
Improving our ability to monitor ocean carbonate chemistry has become a priority as the ocean continues to absorb carbon dioxide from the atmosphere. This long-term uptake is reducing the ocean pH; a process commonly known as ocean acidification. The use of satellite Earth Observation has not yet been thoroughly explored as an option for routinely observing surface ocean carbonate chemistry, although its potential has been highlighted. We demonstrate the suitability of using empirical algorithms to calculate total alkalinity (AT) and total dissolved inorganic carbon (CT), assessing the relative performance of satellite, interpolated in situ, and climatology datasets in reproducing the wider spatial patterns of these two variables. Both AT and CT in situ data are reproducible, both regionally and globally, using salinity and temperature datasets, with satellite observed salinity from Aquarius and SMOS providing performance comparable to other datasets for the majority of case studies. Global root mean squared difference (RMSD) between in situ validation data and satellite estimates is 17 μmol kg−1 with bias < 5 μmol kg−1 for AT and 30 μmol kg−1 with bias < 10 μmol kg−1 for CT. This analysis demonstrates that satellite sensors provide a credible solution for monitoring surface synoptic scale AT and CT. It also enables the first demonstration of observation-based synoptic scale AT and CT temporal mixing in the Amazon plume for 2010–2016, complete with a robust estimation of their uncertainty
Key Uncertainties in the Recent Air‐Sea Flux of CO 2
The contemporary air-sea flux of CO2 is investigated by the use of an air-sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air-sea gas transfer velocity are used to evaluate the combined standard uncertainty resulting from several sources of error. Depending on expert opinion, a standard uncertainty in transfer velocity of either ~5% or ~10% can be argued and that will contribute a proportional error in air-sea flux. The limited sampling of upper ocean fCO2 is readily apparent in the Surface Ocean CO2 Atlas (SOCAT) databases. The effect of sparse sampling on the calculated fluxes was investigated by a bootstrap method; i.e. treating each ship cruise to an oceanic region as a random episode and creating 10 synthetic datasets by randomly selecting episodes with replacement. Convincing values of global net air-sea flux can only be achieved using upper ocean data collected over several decades, but referenced to a standard year. The global annual referenced values are robust to sparse sampling, but seasonal and regional values exhibit more sampling uncertainty. Additional uncertainties are related to thermal and haline effects and to aspects of air-sea gas exchange not captured by standard models. An estimate of global net CO2 exchange referenced to 2010 of -3.0 ± 0.6 Pg C yr-1 is proposed, where the uncertainty derives primarily from uncertainty in the transfer velocit
First results on wave spectral properties from the CFOSAT satellite
International audienceCFOSAT is an innovative satellite mission to be launched on October 29th, 2018. It is presently in the final stage of preparation thanks to a fruitfull Chinese-French cooperation started in 2006. CFOSAT will provide for the first time colocated observations on wind vector, wave spectral parameters (wave spectra and associated parameters) from a combination of two radar instruments (SWIM and SCAT) working in altimeter and wave spectrometer modes (SWIM) and wind scatterometer mode (SCAT). The observation products will offer the opportunity to develop new studies from global observations, as joint analysis of space evolution of wind and waves, detailed analysis of the spectral properties of the wave field (in particular its directionality) and relationship between long waves (measured by SWIM) and short wave properties (indirect information from the normalized radar cross-section). The data will also be used in combination with wave and atmospheric numerical models (through assimilation) in order to improve wave and atmospheric forecast. The information on peak wavenumber, wave direction, directional spread for several wave spectrum partitions, will also be of great interest to study wave/current interactions.During these last years, the algorithms for wind and wave inversion have been prepared in France and China by expert laboratories and space agencies. They are under implementation in mission centers and will be ready to provide products a couple of weeks after the satellite launch. During the conference we will show the very first data sets obtained from SWIM as well as the first validation analysis of wave products. This will include comparisons to wave parameters from model outputs, in situ data and other satellite data (altimeter, SAR) at cross-over points. The focus will be put on the main parameters of the wave spectra (significant wave height, peak direction, peak wavelength)
First results on wave spectral parameters from the CFOSAT satellite
International audienceCFOSAT is a new satellite mission launched on October 29th, 2018. It is developed since 2006 thanks to a fruitful Chinese-French cooperation involving the French Space Agency CNES, the Chinese agencies CNSA and NSOAS, and scientific support from various research laboratories in France and China.CFOSAT will provide for the first time colocated and global observations on the surface ocean wind vector, and ocean wave spectral parameters (wave spectra and associated parameters) from a combination of two Ku-Band radar instruments (SWIM and SCAT) working in altimeter and wave spectrometer modes (SWIM) and wind scatterometer mode (SCAT). The CFOSAT products will offer the opportunity to develop new studies from global observations, such as joint analysis of space evolution of wind and waves, detailed analysis of the spectral properties of the wave field (in particular its directionality) and relationship between long waves (measured by SWIM) and short wave properties (indirect information from the normalized radar cross-section). The data will also be used in data assimilation schemes of wave and atmospheric numerical models (through assimilation) in order to improve wave and atmospheric forecast. The information on peak wavenumber, wave direction, directional spread for several wave spectrum partitions, will also be of great interest to study wave/current interactions and to feed the coastal studies with sea state boundary conditions.During this conference, less than six months after the launch, the first results on the products generated in near real-time by the CNES mission center will be presented. First the data processing principles of the SWIM data and the main products will be recalled. Then, a first assessment of the normalized radar cross-section at near-nadir incidence and of wave products (significant wave height, dominant direction and dominant wave length, for the whole spectra and separated by wave partitions) will be presented. This first assessment of the SWIM products relies on the work of a CAL/VAL team which carries out comparisons between CFOSAT data, satellite altimeter products, wave forecast model products (ECWAM, MFWAM, WW3), in situ data, and other satellite data (such a Sentinel-1 wave mode data)
First results on wave spectra parameters from the CFOSAT satellite
International audienc
The CORA dataset: validation and diagnostics of in-situ ocean temperature and salinity measurements
The French program Coriolis, as part of the French operational oceanographic system, produces the COriolis dataset for Re-Analysis (CORA) on a yearly basis. This dataset contains in-situ temperature and salinity profiles from different data types. The latest release CORA3 covers the period 1990 to 2010. Several tests have been developed to ensure a homogeneous quality control of the dataset and to meet the requirements of the physical ocean reanalysis activities (assimilation and validation). Improved tests include some simple tests based on comparison with climatology and a model background check based on a global ocean reanalysis. Visual quality control is performed on all suspicious temperature and salinity profiles identified by the tests, and quality flags are modified in the dataset if necessary. In addition, improved diagnostic tools have been developed – including global ocean indicators – which give information on the quality of the CORA3 dataset and its potential applications. CORA3 is available on request through the MyOcean Service Desk (<a href="http://www.myocean.eu/"target="_blank">http://www.myocean.eu/</a>)
First results on wave spectra parameters from the CFOSAT satellite
International audienc