Argo (oceanography)
Argo is an observation system for the Earth's oceans that provides real-time data for use in climate, weather, oceanographic and fisheries research.[1] [2] [3] Argo consists of a large collection of small, drifting oceanic robotic probes deployed worldwide. The probes float as deep as 2 km. Once every 10 days, the probes surface, measuring conductivity and temperature profiles to the surface. From these salinity and density can be calculated. The data are transmitted to scientists on shore via satellite. The data collected are freely available to everyone, without restrictions. The initial project goal was to deploy 3,000 probes, completed in November 2007.
International collaboration
The Argo program is a collaboration between 50 research and operational agencies from 26 countries, with the United States contributing over half the total funding (as of December 2004). Argo is a component of the Integrated Ocean Observing System.
Float operation
The Argo program was designed to operate on the same 10-day duty cycle to match the existing satellite measurements of the ocean's sea surface. These satellites, called Topex/Poseidon and Jason 1, measure changes in the surface topography of the ocean. With such measurements, information about temperature, mass redistribution, or surface currents can be inferred. The Argo floats measure subsurface changes in temperature and salinity, hence the float measurements are complementary to the altimetry.
Argo is named after the Greek mythical ship Argo which Jason and the Argonauts use on their quest for the Golden Fleece. The name was chosen to emphasize the complementary relationship of the project with the Jason-1 satellite altimeter.
Although drifting floats had been deployed during the World Ocean Circulation Experiment in the 1990s, Argo floats began to be deployed in earnest in the early 2000s. The target number of 3000 deployed floats was reached during 2006–2007. The number of floats is continually changing as floats are lost or expire, while others are deployed. Nominally, some 750 floats are deployed each year to sustain the system. The floats have a nominal 300-km spacing, although the exact separations depend on the randomness of the float drift.
The Argo temperature and salinity measurements are yielding valuable information about the large-scale water properties and currents of the ocean, including the variability of these properties over time scales from seasonal to decadal.
Profiling
Argo floats drift at a fixed pressure (usually around 1000 metres depth) for 10 days. After this period, within the relatively short time of around two hours, the floats move to a profiling pressure (usually 2000 metres deep) then rise, collecting instantaneous profiles of pressure, temperature, and salinity data on their way to the surface. Once at the surface, the floats remain there for under a day, transmitting the data collected via a satellite link back to a ground station and allowing the satellite to determine their surface drift. The floats then sink again and repeat their mission.
Data communication
Most of the floats use the Argos System of satellites to recover data, though a few are using the newer Iridium satellite constellation. The Iridium system offers significant advantages associated with the much faster data transfer. Since an Iridium float spends only 3 minutes at the sea surface, the opportunity to observe surface currents by tracking the movements of the floats is lost but the trajectories of the floats become more representative of the flow at their parking depth.[citation needed]
Float design
A critical capability of an Argo float is its ability to rise and descend in the ocean on a programmed schedule. The floats do this by changing their effective density. The density of any object is given by its mass divided by its volume. The Argo float keeps its mass constant, but by altering its volume, it changes its density. To do this, a piston is used to push mineral oil out of a float and expand a rubber bladder separating the oil from the ocean water. As the bladder expands, the float becomes less dense than seawater and rises to the surface. Once its tasks at the surface are completed, the float then withdraws the piston and descends again.
An increasing number of the floats also carry other sensors, such as for measuring dissolved oxygen.
The antenna for satellite communications is mounted at the top of the float. Once the float reaches the surface, the float is essentially a spar buoy, allowing the antenna to poke above the sea surface for communication. The ocean is saline, hence an electric conductor, so that radio communications from under the sea surface are difficult.
The nominal life span of an Argo float is five years.
Data access
Argo is unique among research programs in that the real-time data are freely offered to anyone. The data collected by the network are made available with no constraint on use of the data, and most data are available for download within 24 hours of a float measurement. Data can be downloaded over the world wide web from one of two global data servers (OPeNDAP servers[4][5]).
Data format
Even though data are supplied by 24 national programs, all data are available in near real-time in a single format. Argo data are in the native import format of the Ocean DataView suite of programs.[6] Ocean DataView (ODV) is freely available software created by Reiner Schlitzer that offers flexible ways of displaying oceanographic data. Data in other formats are also available, e.g., netCDF. A careful study of the manuals before starting to use the data is essential [7]
Data results
Josh Willis of NASA's Jet Propulsion Laboratory has reported that the Argo system has shown no ocean warming since it started in 2003. "There has been a very slight cooling, but not anything really significant," Willis has stated. [8]
See also
References
- ^ Argo Begins Systematic Global Probing of the Upper Oceans Toni Feder, Phys. Today 53, 50 (2000), DOI:10.1063/1.1292477
- ^ Richard Stenger (September 19, 2000). "Flotilla of sensors to monitor world's oceans". CNN. Retrieved 2007-10-28.
{{cite news}}: Check date values in:|date=(help) - ^ Nature: Artefacts in ocean data hide rising temperatures
- ^ Plot and download realtime Argo data.
- ^ OPeNDAP (dapper) server
- ^ Display Argo data using this free software - Ocean Data View
- ^ Argo data system manuals.
- ^ NPR report
External links
- Argo Portal
- International Argo Information Centre
- Argo at the Scripps Institution of Oceanography, San Diego
- Realtime Interactive Map
- Realtime Google Earth File
- Coriolis Global Argo Data Server - EU Mirror
- FNMOC Global Argo Data server - US Mirror
- NOAA/Pacific Marine Environmental Laboratory profiling float project deploys floats as part of the Argo program, provides data on-line, and is active in delayed-mode salinity calibration and quality control for US Argo floats.
- How Argo views changing conditions in the Gulf of Alaska
- Government of Canada, Department of Fisheries and Oceans, Argo Project
- A New World View Argo explorations article by Scripps Institution of Oceanography
- The Argo Blog
- JCOMMOPS