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GCOS Ocean Surface ECV News: Aquarius Mission Lauched to Measure Ocean Salinity (article) Definition: Salinity - A measure of the quantity of dissolved salts in seawater. It is formally defined as the total amount of dissolved solids in seawater in parts per thousand (0/00) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized. These qualifications result from the chemical difficulty in drying the salts in seawater. In practice, salinity is not determined directly but is computed from chlorinity, electrical conductivity, refractive index, or some other property with a relationship to salinity that is well established. The relationship between chlorinity Cl and salinity S as set forth in Knudsen's tables is S=0.03 + 1.805 CL. In 1940, however, a better expression for the relationship between total dissolved salts Σ and chlorinity was found to be Σ=0.07 + 1.811 CL. In more recent times, with the advent of devices that measure continuous records of conductivity electronically (e.g., CTD or conductivity–temperature–depth profiler), a new “practical salinity scale” has been determined. It is defined in terms of its electrical conductivity relative to a prescribed standard and it is given the units psu, for “practical salinity units.” For most purposes one can assume that the new unit, psu, and the older unit, 0/00, are synonymous. (From the Glossary of Meteorology) Introduction: Global knowledge of sea-surface salinity (SSS) is not adequate. Improvement in SSS analysis accuracy is limited by available technology. New satellite sensors hold promise of improved global coverage, although special in situ observing efforts will be needed to evaluate sustained sensor performance. Networks contributing to global sea-surface salinity observations are:
To address these issues the following Actions are proposed that, through the International Oceanographic Data and Information Exchange (IODE)/JCOMM pilot project Global Ocean Surface Underway Data Pilot Project (GOSUD), and in collaboration with the International Ocean Carbon Coordination Project (IOCCP) and the WCRP CLIVAR, develop a sustained programme for sea-surface salinity measurements on selected SOOP repeat lines, fixed-location buoys and, as appropriate, drifting and other autonomous platforms. The OOPC through the WCRP endorses research efforts to investigate the feasibility of measuring salinity using microwave radiances from space, in particular the current efforts through the Soil Moisture and Ocean Salinity (SMOS) and the Aquarius/SAC-D satellite missions.(Source: WMO/IOC Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (2010 Update) GCOS-138/GOOS-184/GTOS-76/WMO-TD/No. 1523) Ocean Salinity and Climate: Ocean salinity measurements are important because surface salinity and temperature control the density and stability of the surface water. Thus, ocean mixing (of heat and gases) and water-mass formation processes are intimately related to variations of surface salinity. Ocean modelling and analysis of water mass mixing should be enabled by new knowledge of surface-density fields derived from surface salinity measurements. The importance of the ocean in the global hydrological cycle also cannot be overstated. Some ocean models show that sufficient surface freshening results in slowing down the meridional overturning circulation, thereby affecting the oceanic transport of heat. (from the CEOS web site) Satellite Observations: Sea surface salinity is emerging as a new research product from satellite measurements of ocean brightness temperature at L-band (microwave) frequencies. The monitoring of surface salinity from space, combined with the provision of regular surface and sub-surface salinity profiles from in situ observing systems, such as surface ships, buoys, and the Argo array, will provide a key constraint on the balance of freshwater input over the ocean. This will allow for better determination of the marine aspects of the planetary hydrological cycle and the possibility of important ocean circulation changes. New research missions must demonstrate capabilities and pave the way to future continuous, climate-quality data records. To date, there has been no contribution from space-based observations to this variable. ESA and NASA/CONAE (Comisión Nacional de Actividades Espaciales of Argentina) plan to fly demonstrator missions (SMOS and Aquarius/SAC-D) for salinity measurements. CEOS identified two actions in response to the GCOS IP in relation to this measurement: ESA will fly SMOS in late 2009 to demonstrate measurement of the sea surface salinity (and soil moisture) ECV; NASA/CONAE will fly Aquarius/SAC-D in 2010 to demonstrate measurement of the sea surface salinity ECV. CEOS agencies will cooperate in developing future plans for an Ocean Salinity Constellation.(satellite missions) (from the CEOS web site) Additional Information:
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