Prediction and Research Moored Array in the Tropical Atlantic


The experimental program PIRATA (initially « Pilot Research moored Array in the Tropical Atlantic » and named « Prediction and Research Moored Array in the Tropical Atlantic » from 2008) has been implemented in 1997 in the Tropical Atlantic Ocean (Servain et al. 1998). It has been launched in the framework of the international program CLIVAR (CLImatic VARiability and predictability) and implies scientific teams from three countries: France (IRD, in charge of coordination and oceanic cruises, Météo France, with contributions by IFREMER and CNRS/INSU), Brazil (DHN and INPE) and USA (NOAA/PMEL). Financial supports for the program are from the IRD, Météo France, and Observatoire Midi-Pyrénées/Université Paul Sabatier.

The more specific goals of the PIRATA program are:

  1. What are the forcing and coupling mechanisms between the atmospheric and oceanic components on the Tropical Atlantic? In particular, what are the Sea Surface Temperature (SST)'s control mechanisms and what are those of heat fluxes?
  2. What are the influences of these heat fluxes (and of quantities of movement: the wind) on the variability (position and intensity) of the trade winds Inter-Tropical Convergence Zone (ITCZ) and on the convective systems of the Gulf of Guinea (which is of interest to the West African monsoon), and on those of the western region of the basin (which is of interest to rainfall over South America and to hurricanes over West Indies)?
  3. What is the relationship between the variability of the SST and that of the heat content of the Tropical Atlantic, and what is its influence on the various variability modes in this region? In particular, what is the dynamic link between the north and south poles of the meridian variability mode of the Atlantic and between it and the equatorial mode?
  4. What are the teleconnections and their mechanisms between the variability in the Tropical Atlantic region and that in other regions (El Niño Southern Oscillation -ENSO-, North Atlantic Oscillation -NAO-, South Atlantic variability etc.)?

In this framework, the overarching goals of PIRATA are to:

  • improve the description of the intra-seasonal to interannual variability in the atmospheric and oceanic (from the surface down to 500m depth) boundary layers in the tropical Atlantic;
  • improve our understanding of the relative contributions of air-sea fluxes and ocean dynamics to variability in sea surface temperature (SST) and sub-surface heat content at intra-seasonal to interannual time scales;
  • provide a set of data useful for developing and improving the predictive models of the ocean-atmosphere coupled system;
  • document interactions between tropical Atlantic climate and variability outside the region, (e.g. ENSO or the North Atlantic Oscillation);
  • design, deploy, and maintain an array of moored oceanic buoys and collect and transmit a set of oceanic and atmospheric data, via satellite in real-time, to monitor and study the upper ocean and atmosphere of the tropical Atlantic.

After a "pilot phase" from 1997 to 2001, the institutions in the three supporting countries decided to extend the array maintenance for a 5-year "consolidation phase" to allow for a meaningful demonstration that the data would contribute significantly to both scientific research and operational applications. This "consolidation phase" has been extended until February 2008. A PIRATA Resources Board (PRB) has been established in 1999 to answer to the objectives of the commitments (financial, human, vessel time...) signed between involved institutions. A Memorandum of Understanding (MoU) has been officially signed in August 2001 by the institutions representatives. This MoU commited the responsability of partners during the whole consolidaton phase of PIRATA (2001-2006 then 2008). From 2006 to 2008, after a very positive scientific evaluation of the PIRATA program by CLIVAR and OOPC (established from the document : Bourlès et al., 2006), a new Memorandum of Understanding, has been written and signed by the four organisms (France: IRD and Météo-France ; Brazil: INPE ; and USA: NOAA) the 2nd February, 2009 during the PIRATA 14 meeting organized in Toulouse (see The meeting PIRATA-14 report), so ensuring the maintenance of the program until 2013. After 10 successful years of the program, a synthesis paper has been published in 2008 (Bourlès et al., 2008) and the PIRATA initial denomination has been modified in "Prediction and Research Moored Array in the Tropical Atlantic".

The french component of PIRATA was, from 2001 to 2009, recognized as a national ORE (Environment Research Observatory) by INSU/CNRS. In late 2009, PIRATA has been positively reviewed by CIOE and obtained in 2010 the new SOERE label (System of Observation and Experimentation, on the long term, for Environmental Reseach). IRD and MeteoFrance are associated through a convention, renewed every 4 years (the present convention is running until fall 2012).

From 1997 to 2005, PIRATA mainly consisted in the servicing of an observation network of 10 Autonomous Temperature Line Acquisition System (ATLAS) moored buoys (similar to the ones used in the tropical Pacific in the framework of the TOGA program ; (see http://www.pmel.noaa.gov/tao). These 10 meteorological and oceanic buoys are localized in order to resolve the two main modes of tropical Atlantic climate variability: the equatorial mode and the meridional mode. From 2005, the PIRATA network largely extended. As early as 2001-2002, a PIRATA Southwest Extension has been proposed by Brazil, and a Southeastern Extension has been proposed by South-Africa. In 2005, three ATLAS buoys have been deployed in the SouthWestern region of the Tropical Atlantic basin, off Brazil, under the responsibility of this country. The Southeastern Extension, presented by South Africa (CapTown university) and funded for a one-year period by the BCLME (Benguela Current Large Marine Environment) program, has been implemented in June 2006 and retrieved in June 2007 by IRD, during the EGEE3 and EGEE 5 cruises. NOAA/AOML (USA) also proposed an extension of the ATLAS buoys network in the Northern and Northeastern regions of the Tropical basin, with 4 buoys deployed in 2006 and 2007.

Thus, the PIRATA network consists now in 17 ATLAS buoys, 2 currentmeter moorings, meteorological stations and tide gauges (see map below).

PIRATA is now recognized at an international level as the backbone network for meteo-oceanic measurements needed for studies related to seasonal to decadal climatic processes at the Tropical Atlantic basin scale, planed in the framework of international programs as AMMA (Analyse Multidisciplinaires de la Mousson Africaine, 2005-2010), TACE (Tropical Atlantic Climate Experiment, 2007-2011), CLIVAR, OOPC, GOOS, CCOS etc.

The PIRATA backbone of ATLAS buoys (red squares), Northeast Extension (blue stars), Southwest Extension (green circles), Southeast Extension pilot project (yellow triangle), and island-based observation sites (green crosses). Buoys with barometers and the ability to estimate net heat flux are indicated with black circles. Also currentmeter moorings are maintained at 23W-Equator (PIRATA-international) and 10W-Equator (PIRATA-France, initially installed in relation with the EGEE/AMMA and TACE/CLIVAR programs).

The PIRATA program provides to the scientific community a free access to many data, summarized as follows:

  1. Real time data:
    • Meteo-oceanic measurements using ATLAS buoys: The ATLAS buoys are designed to measure surface meteorological variables (wind direction and speed, air temperature and humidity, rainfall and solar radiation) and hydrological sensors between the surface and 500m, namely 2 pressure sensors (at 300m and 500m), 11 temperature sensors (at the surface, 20m, 40m, 60m, 80m, 100m, 120m, 140m, 180m, 300m and 500m) and 4 conductivity sensors (at the surface, 20m, 40m and 120m). The mean daily observations are transmitted by satellite via Argos and are available in near real-time via Internet.
    • Meteorological measurements from meteorological stations: data from the two automatic meteorological stations located at Fernando de Noronha Island and St. Peter & St. Paul Rocks, are transmitted by Brazil's SCD satellites at 3-hourly interval, and data available in near real time via internet.
    • Sea level measurements: At São Tomé (6°30'E-0°N), a tide gauge station transmits daily via Argos hourly measurements of sea level, sea surface salinity and temperature along with atmospheric pressure.
    • (see the following website).

  2. Delayed data:
    • Current-meter measurements from moorings: Since late 2001, a mooring located at 23°W-0°N ATLAS is equipped with an ADCP (Acoustic Doppler Current Profiler) which continuously measures the two horizontal components of the current, from the surface to approximately 130m. The in situ measurements are available at a rate of one measurement every 4m from a depth of 16m.
    • Oceanographic measurements obtained from ships: During each oceanographic campaign dedicated to PIRATA, meteo-oceanic measurements are carried out, which are principally : Current measurements (from 0 to 700m max.) using VM-ADCP acoustic Doppler current profilers; Surface temperature and salinity measurements using a thermosalinograph; Meteorological and navigational measurements using data acquisition units; Hydrological measurements with CTD profiles (continuous pressure, temperature and salinity measurements between the surface and 500m or 1000m); Temperature measurements between the surface and approximately 800m with XBT probes.
    • (see the ftp server).

The PIRATA network maintenance induces the realization (from the French side) of at least one dedicated oceanographic cruise per year, and at now 20 cruises have been carried out from 1997 (from 2005 to 2007, PIRATA cruises were associated to the cruises of the EGEE program, oceanographic part of the international AMMA program). In France, the maintenance of the 5 PIRATA network ATLAS buoys located east of 23°W has to deal with two kinds of problems: 1) the problems due to vandalim in the Gulf of Guinea (linked to fishery activities; see http://www.brest.ird.fr/actualites/EGEE-3_bouees.htm), and 2) the problems due to the national fleet vessel time availability. This last problem is now resolved since 2006, thanks to the IRD R/V ANTEA repairs.

PIRATA already allowed numerous studies carried out within several French laboratories, about air-sea fluxes, oceanic processes, and also data assimilation techniques, notably in the framework of the MERCATOR project.

References :

Servain J., A. Busalacchi, A. Moura, M. McPhaden, G. Reverdin, M. Vianna, & S. Zebiak: A Pilot Research Moored Array in the Tropical Atlantic "PIRATA" ; The Bulletin of American Meteorological Society. 79, 2019-2031, 1998.

Bourlès, B., A. J. Busalacchi, E. Campos, F. Hernandez, R. Lumpkin, M.J. McPhaden, A.D. Moura, P. Nobre, S. Planton, J. Servain & J. Trotte, PIRATA (Pilot Research Moored Array in the Tropical Atlantic): Accomplishments of PIRATA: 1997-2005, Status and perspectives, Document prepared for a PIRATA review by CLIVAR -AIP - and OOPC, 89pp, avril 2006.

Bourlès, B., R. Lumpkin, M.J. McPhaden, F. Hernandez, P. Nobre, E. Campos, L.Yu, S. Planton, A.J. Busalacchi, A.D. Moura, J. Servain, and J. Trotte, The PIRATA program: history and accomplishments of the 10 first years tropical Atlantic observing system's backbone, Bulletin of the American Meteorological Society, 89(8), 1111-1125, doi/10.1175/2008BAMS2462.1, 2008.