Argo (oceanography)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Argo Logo.png

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.

Map of the Argo float network as of February 2013

Contents

International collaboration [edit]

The Argo program is a collaboration between 50 research and operational agencies from 31 countries (shown on the graphic above). Argo is a component of the Integrated Ocean Observing System.

Float operation [edit]

The Argo program was designed to complement satellite measurements of sea surface height.

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 3,000 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.

Example profiles of temperature and salinity obtained from an Argo float in the central North Pacific (38.4°N, 155.3°W) on April 8, 2005.

Profiling [edit]

Argo floats drift at a fixed pressure (usually around 1,000 metres depth) for about 9 days. After this period, within the relatively short time of around two hours, the floats move to a profiling pressure (usually 2,000 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, which repeats each 10 days.

Data communication [edit]

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.

Sensors [edit]

As different types of floats are used, sensor equipment varies. As an example, Bio-Argo floats have, in addition to temperature and salinity, optical sensors to quantify chlorophyll and backscattering.[4]

Float design [edit]

A so-called Argo-float.[5] The height of the float is about 2 m.

The 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 hydraulic piston is used to push mineral oil out of the float and expand a rubber bladder at the bottom end of the float. As the bladder expands, the float becomes less dense than seawater and rises to the surface. Upon finishing its tasks at the surface, the float withdraws the piston and descends again.[6]

Early designs for stationary profiling bouys utilized compressed air to change the buoyancy characteristics of the floats.[7]

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. After the internal batteries expire, the floats are allowed to sink to the ocean floor or wash ashore, though having a float wash ashore is very rare.

Data access [edit]

Argo 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 servers which can be found here.

Data format [edit]

Even though data are supplied by 31 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 Data View (ODV) suite of programs.[8] Ocean Data View (ODV) is proprietary but 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.

Data results [edit]

It is not yet possible to use Argo data to detect global change signals, as the dataset is not yet long enough to observe global change signals.[9]

Argo data result errors [edit]

During 2006, the Argo Network was thought to have shown a declining trend in ocean temperatures.[10] In February 2007, the author of the paper, Josh Willis, discovered that there were problems with the data used for the analysis.[11] After eliminating incorrect data, the trend to that time remained cooling, but below the level of statistical significance.[3]

Data results from year 2008 and after [edit]

Takmeng Wong and Bruce A. Wielicki published a paper on the Argo data corrections in the NASA journal "The Earth Observer, 20(1), 16-19".[12] Josh Willis, in an article published on the NASA Earth Observatory web site states that after correcting the errors in the Argo thermometer measurements, the results show that the world's oceans have been absorbing additional energy and have been warming.[3][11]Rebecca Lindsey (November 5, 2008). "Correcting Ocean Cooling". NASA. Archived from the original on 30 June 2011. Retrieved 18 July 2011. 

See also [edit]

References [edit]

  1. ^ Argo Begins Systematic Global Probing of the Upper Oceans Toni Feder, Phys. Today 53, 50 (2000), doi:10.1063/1.1292477
  2. ^ Richard Stenger (September 19, 2000). "Flotilla of sensors to monitor world's oceans". CNN. Archived from the original on 6 November 2007. Retrieved 2007-10-28. 
  3. ^ a b c 2007, Nature: Artefacts in ocean data hide rising temperatures
  4. ^ Bio-Argo Chlorophyll, backscattering, CDOM and irradiance measurements on profiling floats
  5. ^ "Argo-float design". Retrieved 2012-09-17. 
  6. ^ "How Argo Floats Work". UCSD. Retrieved 2009-12-15. 
  7. ^ Kery, SM (1989). "Diving in support of buoy engineering: The RTEAM project". In: Lang, MA; Jaap, WC (ed). Diving for Science…1989. Proceedings of the American Academy of Underwater Sciences annual scientific diving symposium 28 September - 1 October 1989 Wood Hole Oceanographic Institution, Woods Hole, Massachusetts, USA. Retrieved 2013-04-16. 
  8. ^ Display Argo data using Ocean Data View
  9. ^ argo.ucsd.edu: How well is Argo able to observe global ocean changes?
  10. ^ Oceans cool off in hottest years. Quirin Schiermeier. Nature 442, 854-855 (24 August 2006) | doi:[http://dx.doi.org/10.1038%2F442854a 10.1038/442854a; Published online 23 August 2006] Quote "...Temperature drop puzzles climate researchers...But assuming the trend is real, what caused the cooling and where did the heat go?..."
  11. ^ a b Nasa.gov: November 5, 2008 Correcting ocean cooling Quote: "...According to the float data on his computer screen, almost the entire Atlantic Ocean had gone cold. Unless you believe The Day After Tomorrow, Willis jokes, impossibly cold...page 3 "First, I identified some new Argo floats that were giving bad data...He was supposed to fly to Colorado that weekend to give a talk on "ocean cooling" to prominent climate researchers. Instead, he'd be talking about how it was all a mistake...What we found was that ocean heating was larger than scientists previously thought, and so the contribution of thermal expansion to sea level rise was actually 50 percent larger than previous estimates."..."but also because the problems with the newest Argo data—the problems that Josh Willis found as well as other problems we have identified—haven't been totally solved. For the most recent years [2003-2007], the sea level budget once again does not close. Our team is still working on that problem."..."
  12. ^ Unscrambling the cause of recent ocean cooling with net radiation observations from the CERES instrument on the Terra satellite. NASA. February, 2008. Retrieved 18 July 2011. 

External links [edit]

Wikimedia Commons has media related to: Argo (oceanography)
 
Landforms
Antarctic bottom water hg.png
Plate tectonics
Ocean zones
Sea level
Acoustics
Other
Retrieved from "http://en.wikipedia.org/w/index.php?title=Argo_(oceanography)&oldid=550747543"