Argo (program)

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Argo is a mobile observation system for the world's oceans that has been used to measure temperature, salinity, currents and, increasingly, chemical and biological components since 2000. The data, transmitted almost in real time, are used in research and climate monitoring.

Map of the Argo network in February 2018

Argo comprises a fleet of over 3960 automated floating buoys ( called profiling floats in English ) that are distributed across all oceans (as of June 2020). These measuring robots are relatively small and weigh between 20 and 30 kg. All floating buoys belonging to the Argo program are subject to a common data policy, and the data is publicly available in real time and without restriction. The majority of the floats drift to depths of 1000 m (the so-called parking depth) and first descend to 2000 m every ten days and then rise from this depth to the surface of the sea. During the ascent, the floats measure the temperature, conductivity and pressure in the water column. On the basis of this measurement data, the salinity and density of the seawater can also be calculated. Density is an important parameter in oceanography, as horizontal density differences drive the large-scale currents in the ocean.

The mean flow field in the parking depth can be determined from the distance covered and the direction of successive float positions. The positions are not measured in the parking depth, but only on the surface by the positioning systems of the GPS or ARGOS satellites. Data is also transmitted via satellite to the international data network, where all information is collected, quality checked in real time and then made available for use.

The Argo program is named after the ship Argo from Greek mythology, with which the king's son Jason went in search of the golden fleece . The name therefore emphasizes the close connection between the oceanic measuring system and the Iason satellite system , with which the sea surface topography is measured from space. In some literature sources, Argo is incorrectly used as an acronym .

International cooperation

The Argo program is a joint project of more than 30 nations from all over the world (see graphic above right). Only this cross-border cooperation enables global monitoring of the world's oceans, and Argo is therefore a core component of the global ocean monitoring system GOOS. Argo is coordinated by an international steering group, the Argo Steering Team, which consists of scientists and technical experts. The data streams are managed by the Argo Data Management Team. Overall coordination is carried out by the Argo Information Center (AIC), which is part of the Intergovernmental Oceanographic Commission (IOC) and the World Meteorological Organization (WMO).

Internationally, Argo is involved in other important climate observation programs such as GEO (The Group of Earth Observation), the CLIVAR project belonging to the World Climate Research Program , which deals with the variability and predictability of the ocean-atmosphere system, and GODAE, the project that deals with the assimilation of ocean data.

An animation for children about how Argo works was created in 2014 by IMOS ( Integrated Marine Measurement Strategy , Australia).

history

Image of an Argo floating buoy

The original plan for the Argo program was first presented at the 1999 OceanObs conference. The aim of this conference was to ensure coordination of ocean observations with the involvement of various international agencies. The original floor plan for the Argo program was drawn up by a small group of scientists led by Dean Roemmich. This plan envisaged a global observation system consisting of 3,000 propellants and set the target for its implementation in 2007. In fact, a float density of 3000 buoys was reached in 2007 and thus the global coverage of the world ocean. The steering group (Argo Steering Team) met for the first time in 1999 and developed the guidelines for global data transfer. Ten years later the steering group delivered a status report at the OceanObs conference 09 and discussed proposals for the further development of the system. The proposals included the expansion of the observation system to the high latitudes, to marginal seas such as the Gulf of Mexico and the Mediterranean, increased sampling of the equatorial areas and the strong marginal currents ( Gulf Stream , Kuroshio ). Furthermore, the sampling of the deep ocean (> 2000 m) and the deployment of additional sensors to measure biological and chemical parameters were discussed.

In November 2002, an Indian Argo Float delivered the one millionth profile. This is twice as many profiles as all oceanographic measurements from research vessels in the 20th century combined. This event was recognized in various press releases. Since 2014 there has been a strong expansion of biological measurements in the BioArgo program.

Float design / functionality

Schematic section through an Argo probe. Height around 2 m. The measuring and communication facilities are located in the upper third. The horizontal disk is used for stabilization. Red is the buoyancy control system. The blue cylinders in the lower half are the batteries.

The ability of an Argo float to rise and fall is achieved by changing the density. The density of an object is defined as its mass divided by its volume. Since the mass (weight) of a float remains unchanged, it can only change its density by changing its volume. This takes place through the hydraulic expansion of a plastic bladder filled with oil. To do this, mineral oil is pumped from the pressure-protected housing of the float into the plastic bladder at the end of the float and inflates it. When this bubble then expands, the float loses density and rises to the surface. Once it has reached the surface and the data has been transferred, the oil is pumped back into the pressure hull and the descent begins. The antenna for satellite communication is mounted at the top of the float so that it is clearly visible from the water when the ascent is finished. The lifetime of a float has increased from four to six years since the program began.

Floats are only made by a limited number of companies and organizations. The most commonly used APEX floats are manufactured by Teledyne Webb. The SOLO and SOLO-II floats were developed by the Scripps Institution of Oceanography . Other types include the NINJA floats developed by the Japanese company Tsurumi Seiki Co , the PROVOR floats, which were developed in France at the Ifremer, and the German NEMO floats. Most floats use sensors supplied by Sea-Bird Electronics . Sea-Bird recently added its own float called NAVIS. A typical Argo Float is approx. 1 m long and 14 cm in diameter.

All Argo floats carry sensors that measure temperature and salinity, but a growing number of floats also carry additional sensors, such as for measuring dissolved oxygen in the ocean and other sensors that are of interest for biological or chemical issues, such as chlorophyll, Nutrients and pH . These are summarized in the expansion of the Argo program as BioArgo and are still in the implementation phase. With these additional measurements, the biological and chemical components of the sea can then also be monitored.

Array design

Number of profiles created with Argo drifters south of 30 ° S (upper curve) compared to profiles collected with other measuring probes (lower curve). Particularly noteworthy is the elimination of the seasonal bias in the Argo profiles compared to the other measuring probes.

The original plan envisaged an average distance between the floats of 3 degrees longitude and 3 degrees latitude. With these specifications, a higher resolution (in km) is achieved at higher latitudes, which is necessary because the vortex radius also decreases towards the poles. Although the set number of 3,000 floats was reached in 2007, there are still spatial inequalities and too few floats are laid out in the Southern Ocean.

Work is underway to extend the original plans to the entire world ocean, but this is particularly difficult for the southern ocean, as it is difficult to access and there are few ships available for laying out the floats.

As already mentioned in the history section , work is being carried out to strengthen the measurements in the area of ​​the equator, the marginal currents and the marginal seas. In order for this to be implemented, a number of around 4000 floats are required. This target has been achieved in recent years.

An outstanding feature of the Argo program is the fact that the floats measure all year round, thus reducing the seasonal bias in the observations that existed with ship-based measurements. The opposite diagram shows the number of Argo profiles per month that were collected south of 30 ° S (upper curve) from the start of Argo measurements until November 2012. In comparison, the measurements from other measurement methods are shown. This strong seasonal bias is clearly evident in the lower curve, with around four times as many measurements being carried out in the southern summer as in the southern winter.

Data access

A special feature of the Argo program is the global and unrestricted data access in almost real time. As soon as a float has sent data, it is immediately transferred into a format so that it can be fed into the GTS system (Global Telecommunications System) . The GTS is operated by the World Meteorological Organization (WMO) and is used to share data for weather forecasting between national agencies. This means that the Argo data is available to all nations that are members of the WMO within a few hours of their transmission. The data is also available via ftp and www access from the two global Argo data centers (GDACs) www.coriolis.eu.org in France and www.usgodae.org/argo/argo.html in the USA.

Over 90% of the globally transmitted profiles can be called up within 24 hours, the remaining 10% with a slightly larger time lag.

The scientists who transferred the data from the GTS or the GDACs should have sufficient programming knowledge to be able to process the data further. The data format provided by the GDACs can e.g. B. can be visualized with programs such as Ocean DataView . Every day files are compiled in the data centers, in which all profiles of the respective day are summarized by ocean. An example of this would be the file 20121106_prof.nc, which would have contained all profiles for November 6, 2012. These files are routinely created for the Atlantic, Pacific and Indian Oceans.

A recent salinity section along the date line in the Pacific. The data shown are based on Argo measurements and are presented using the Global Marine Atlas.

For users without programming knowledge who want to analyze Argo data, ready-made products such as the Argo Global Marine Atlas are available, which offer user programs with which z. B. the salinity section (as shown on the right) can be prepared graphically. In addition, these user programs offer many other options, such as the display of horizontal maps and time series. The Argo Global Marine Atlas is maintained by the Scripps Institution of Oceanography in La Jolla, California.

Argo data can also be displayed in Google Earth using layer files developed by the AIC.

Regardless of the selected data set and the respective display program, all users are advised to inform themselves about the structure of the Argo data files, the functionality of the floats and the meaning of the quality flags. The Argo User's manual is available for this purpose. It is strongly recommended that you study this manual carefully before performing any analysis on the Argo data. In addition, there is a webpage which is maintained by the steering group and which provides useful tips for the Argo beginner.

Results

Number of scientific publications per year based largely or entirely on Argo data and published in refereed journals.

Argo is the primary source of information about the climatic condition of the ocean and is used worldwide, as can be seen from the large number of publications (see figure on the right). These studies cover a wide variety of topics, such as ocean-atmosphere interaction, ocean currents, annual fluctuations, El Niño , mesoscale eddies, water mass properties, and water mass formation. For the first time, the amount of Argo data is sufficient to determine the global heat content of the ocean. Argo data also flow into computer models for the climate system and thus serve to improve seasonal forecasts.

As an example of scientific questions, reference is made to a manuscript by Durak and Wijffels, which analyzes the global changes in surface salinity. A significant result of this work is the realization that areas with high salinity become even more salty and areas with low salinity show a further decrease in salinity. The distribution of salinity is determined by the differences between precipitation and evaporation. The results presented here therefore imply that the hydrological cycle in the components precipitation and evaporation must have strengthened as a result of climate change.

Argo data were essential for the analyzes in Chapter 3 of the IPCC's 5th Assessment Report, which was published in September 2013. In the appendix to this chapter of the status report it is pointed out that the quality and volume of oceanic measurements have fundamentally improved through the implementation of the Argo program. Only through these improvements is it possible to analyze the heat budget in the upper part of the ocean or changes in surface salinity with sufficient accuracy.

From 2014, a new generation of Argo buoys, designed for diving depths of 4000 to 6000 meters, was initially used on a test basis. The task of these so-called "Deep Argo" floats is to record the temperature and flow patterns of the deep sea areas and, in particular, to transmit precise data on the changing heat content of the oceans in these water layers.

Web links

Commons : Argo (oceanography)  - collection of images, videos and audio files

Individual evidence

  1. Toni Feder: Argo Begins Systematic Global Probing of the Upper Oceans . ( Memento of the original from July 11, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Phys. Today , 53, 2000, p. 50, doi: 10.1063 / 1.1292477 @1@ 2Template: Webachiv / IABot / www.aip.org
  2. ^ Richard Stenger: Flotilla of sensors to monitor world's oceans . In: CNN , September 19, 2000. Archived from the original on November 6, 2007. Retrieved October 28, 2007. 
  3. If Argo was an acronym it would be spelled "ARGO" which the Argo Steering Team officially discourages. An acronym (Array for Realtime Geostrophic Oceanography) is occasionally cited but this arose post hoc after the name was chosen solely because of its relationship to Jason.
  4. GOOS global ocean monitoring system
  5. Argo Steering Team
  6. Argo Information Center (AIC)  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / arg.jcommops.org  
  7. animation on YouTube
  8. Floor plan of the Argo program (PDF)
  9. ^ Argo - A Decade of Progress . ( Memento of the original from October 17, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) community white paper submitted to OceanObs'09  @1@ 2Template: Webachiv / IABot / abstracts.congrex.com
  10. ^ British Oceanographic Data Center Celebrates One Million Profiles.
  11. UNESCO Celebrates One Million Argo Profiles.
  12. ^ Scientists Launch Bio-robots in the Indian Ocean - A Guardian report.
  13. UCSD description on "how Argo floats work"
  14. BioArgo ( Memento of the original from October 17, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.oao.obs-vlfr.fr
  15. original plan (PDF)
  16. ^ Argo - A Decade of Progress . ( Memento of the original from October 17, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) community white paper submitted to OceanObs '09  @1@ 2Template: Webachiv / IABot / abstracts.congrex.com
  17. ODV home. Retrieved April 24, 2014 .
  18. ^ Argo Global Marine Atlas by Megan Scanderbeg
  19. Users interested in grid fields can find a selection of fields on the page .
  20. instructions for using these files are here to find.
  21. Argo User's manual (PDF)
  22. Tips  ( page can no longer be accessed , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. at www.argo.ucsd.edu@1@ 2Template: Dead Link / www.argo.ucsd.edu  
  23. GODAE / Ocean View
  24. ^ PJ Durack, SE Wijffels, RJ Matear: Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000. In: Science, 336, 2012, pp. 455-458, online.
  25. Caitlyn Kennedy: Deep Argo: Diving for Answers in the Ocean's Abyss. In: climate.gov (NOAA). 2015, accessed July 1, 2020 .