Array of Floats Collects One Millionth Data Profile
In the late nineties a group of scientists planned to maintain a network of 3,000 units, in ice-free areas, providing both real-time data and higher quality delayed mode data and analyses to underpin a new generation ocean and climate models. In 2007 the 3,000 float target was reached and the array has remained above 3,000 floats. The project is known as Argo. Argo floats are gathering profiles of temperature and salinity together with information on subsurface water movement at the rate of 1 profile approximately every 4 minutes, (360 profiles per day or 11,000 per month) and on 4 November 2012 the array passed the symbolic milestone of collecting its 1 millionth profile. In the late 19th century, ships have collected just over half a million temperature and salinity profiles to a depth of 1km and only 200,000 to 2 km. At the present rate of data collection, Argo will take only 8 years to collect its next million profiles. It will provide a quantitative description of the changing state of the upper ocean and the patterns of ocean climate variability from months to decades, including heat and freshwater storage and transport. The data will enhance the value of the Jason altimeter through measurement of subsurface temperature, salinity, and velocity, with sufficient coverage and resolution to permit interpretation of altimetric sea surface height variability. Argo data will be used for initializing ocean and coupled ocean-atmosphere forecast models, for data assimilation and for model testing. A primary focus of Argo is to document seasonal to decadal climate variability and to aid our understanding of its predictability. A wide range of applications for high-quality global ocean analyses is anticipated. The data come from battery-powered autonomous floats that spend most of their life drifting at depth where they are stabilized by being neutrally buoyant at the "parking depth" pressure by having a density equal to the ambient pressure and a compressibility that is less than that of sea water. At present there are three models of profiling float used extensively in Argo. All work in a similar fashion but differ somewhat in their design characteristics. At typically 10-day intervals, the floats pump fluid into an external bladder and rise to the surface over about 6 hours while measuring temperature and salinity. Satellites determine the position of the floats when they surface, and receive the data transmitted by the floats. The bladder then deflates and the float returns to its original density and sinks to drift until the cycle is repeated. Floats are designed to make about 150 such cycles.