Deployments

Deployed floats :

Since the early 2000's, around 1700 European ARGO floats have been deployed in a number of different geographic areas.

If you want to see where those floats have been deployed, download this file and open it with Google Earth (if you don't have Google Earth Tool installed in your computer, go to the Google Earth website to download it before). As you can see from the screenshot on the right, this tool (updated on 2015/06/21) will allow you to : 

 

  • see active (724), inactive(1872) or/and planned (200) Euro-Argo floats,

 

  • select individual float and by clicking on it, get a 'baloon pop-up' with information about the float, thumbnail plots of the float data, and links to larger plots and hints on how to interpret the data.

 

Deployments have been focused on meeting specific European requirements while also contributing to the global array. In particular, Italy has coordinated the deployments of more than 60 Argo floats in most areas of the Mediterranean and Black seas, mainly using ships of opportunity.

Figure 1 : Argo vs Euro-Argo Yearly Deployments since 2001 (source : Argo Information Center)

Figure 2 : Evolution of Argo vs Euro-Argo Total Deployments since 2001 (source : Argo Information Center)

Compared to the actual ARGO array of more than 3000 floats, Euro-Argo has provided a significant contribution to the growing Argo array, contributing by more than 1/3 fo the global array. Plans for years 2012-2019 aim to reach progressively 250 floats deployed per year, which would strengthen the importance of a long-term European contribution to the ARGO network.

 

Strategy for float deployment in marginal and Nordic seas :

While the Argo strategy for the open ocean has been defined and agreed at international level, the sampling strategy in areas of European interest (Nordic Seas, Mediterranean and Black Seas) have been defined and validated.

  • Nordic Seas pose specific challenges due to the complex topography, and the weak mean stratification. An analysis of Argo floats deployed since 2001, providing more than 4300 vertical profiles of temperature and salinity, have been conducted. The results from the analyses of the float data can be summarized as follows: meso-and sub-mesoscale variability cannot be resolved by any financially and logistically reasonable float programme. This variability has to be treated as noise. The mean seasonal variability of both the circulation and the stratification is resolved by the present float data set. The data set also indicates inter-annual changes of the seasonal cycle of the hydrographic parameters. Analysis of ship-borne hydrographic surveys indicate that at least six floats have to be present in each basin in order to reduce the uncertainties below the signal level. Long-term (over a decade) changes of heat- and freshwater contents are also detected in the float time series.

 
In conclusion it is advised to operate at least 3-4 floats in each of the Nordic Seas basins at any time. The inherent danger of loss of floats, due to encounters with sea ice in particular during winter and spring, would make a population of 4-5 floats per basin desirable.

 

  • Mediterranean and Black Seas : a strategy has been proposed, based on a study of historical Argo data in the Mediterranean , and of simulated Argo float trajectories in a circulation model of the Mediterranean for years 2004 to 2007. Robust statistics of temperature and salinity can only be obtained with a large number of float dispersed quasi-uniformly in all the areas, but monitoring the Mediterranean and Black Seas with hundreds of floats is not practically possible due to logistical and economical reasons. In contrast, the observed trends in the deep layers of the Mediterranean characterized by less spatial variability, suggest the opportunity to increase the observations at great depths with the Argo network.

 

Despite the problem of under-sampling, the following recommendations for the continuation of the
Argo program in the Mediterranean Sea can be advised :

  1. Maximum profiling depth of 2000 m at every cycle or every two cycles, with a short 700 m profiles in between;
  2. Deployment in deep waters (depth > 2000 m);
  3. Cycles of 5 days is a good compromise to capture more variability of the sub-surface velocity field and to obtain a robust estimate of the mean velocity at parking depth.
  4. Parking depth between 300 and 400 m to track the Levantine Intermediate Water throughout the Mediterranean;
  5. Use Argos-3 or Iridium telemetry to reduce surfacing time (from about 6 h to less than one hour) and probability of hazards (stranding, theft by seafarers, etc.);
  6. Maintain a minimum population of 30/50 floats in the Mediterranean. If Argos-3 or Iridium telemetry is used, the “mortality” of the floats should be reduced and reseeding of 5/10 floats per year might be sufficient.
  7. Deploy the floats inside and outside the significant circulation structures (with sub-basin scale of about 100 km) such as the instability eddies of the Algerian and Lybio-Egyptian Currents, in order to obtain unbiased statistics.

 

The breakdown of float types :

The breakdown of float types being used in the whole of the international ARGO programme and the Euro-Argo component in February 2010 is as follows :