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Summary

Opening of the meeting

Summary of current conditions in the Tropical Pacific

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Acknowledgments

Atlantic Circulation and Climate Experiment (ACCE) Plans for Profiling ALACE Float and Global Lagrangian Drifter Arrays in the Tropical and Subtropical North Atlantic Ocean
M. Swenson, NOAA/AOML, U.S.A.
An ambitious array of profiling ALACE floats has been proposed as part of the ACCE (Figure 8). A low-resolution array is expected to be deployed on a (600 km)2 resolution beginning FY 1997 and continuing through FY 2000, with 48, 76, 20, and 20 instruments, respectively expected to be deployed each year. During the first two years, 23 and 42 of the units will also be equipped with salinity sensors.

Plans for deployment of 160 Global Lagrangian Drifters for ACCE over FY 1997 FY 1999 are motivated by the desire to obtain a basin wide data set of at least 3 buoy-years of data per 5° x 5° bin, which will lead to estimates of the mean velocity field (away from intense current regions) that have a sampling error of 2-3 cm/sec at one standard deviation. The region north of 20°N has been sampled since 1991 (Figure 9) and plans exist for other deployments in this region, so most ACCE deployments will be targeted for the tropical Atlantic. In addition, 80 Global Lagrangian Drifters are planned to be deployed in the region 0° 12°N as part of a study of the cross-gyre exchange mechanism.

• A study of the relative importance between ocean dynamics and surface heat fluxes in determining the evolution of cold tongue SSTs will deploy on the equator, near an existing ATLAS mooring, a downward looking 600 kHz ADCP to obtain, with high vertical resolution, upper ocean currents over a 6 month to 1 year period. Together with data from the TAO Array, this will allow detailed investigations of the nature of the near surface shear and its relationship to the local wind stress.
• The temporal and spatial variability of the air-sea fluxes and the upper ocean will be examined by collecting one-year long time series of fluxes of momentum, heat, fresh water, upper ocean temperatures, velocities, and salinities using IMET moorings deployed along 125°W. One mooring will be at 10°N, which places it in the ITCZ for much of the year, a region characterized by high precipitation rates and warm sea surface temperatures. The second mooring will be in the equatorial cold tongue (0° 2°N), a region of clear skies and very little precipitation except during strong ENSO episodes.
• A shipboard measurement program will be conducted during the boreal summer to determine the vertical structure of precipitating clouds of the eastern Pacific ITCZ in comparison to those of the western Pacific warm pool. A ship equipped with a 5 cm wavelength scanning Doppler precipitation radar and other meteorological instrumentation will occupy a site for 3 to 4 weeks in the ITCZ, nominally in the vicinity of 125°W and 8°N.

The PACS Implementation Plan is presently under development. The period immediately after the above programs (e.g., 1998 - 2000) will include a major observational program focussed on the ITCZ/Cold Tongue complex in the extreme eastern Pacific and will utilize the in situ observations provided by the TAO Array along 95°W, supplemented by shipboard observations and aircraft (manned and, possibly, unmanned) based out of the Galapagos Islands, southern Mexico and/or Costa Rica. Included within this study is the region of extreme deep convection centered over the Panama Basin, southern Central America, and northwest South America. Plans under consideration include augmenting the existing radiosonde network in the region and establishing two sounding stations on islands in the region. This program may be further augmented with periodic dropsonde missions flown by the NOAA Gulfstream IV aircraft out of Tampa, Florida.

Plans are also under consideration to extend the proposed Atlantic Circulation and Climate Experiment with PACS support for some observations from 5°N to 5°S. Longer range proposals include more comprehensive atmospheric observations in the extreme western tropical Atlantic.

For the Atlantic Ocean, it is intended that the French CLIVAR studies be mainly related to the heat and mass transport associated with two branches of the "Conveyor Belt," including the formation of cold deep waters in the Labrador and Irminger seas.

More specifically for the tropical Atlantic, an ORSTOM group of oceanographers initiated a proposal to investigate the following set of problems.

Surface and Subsurface Variability Studies

• What are, in the tropical Atlantic, the portion of the interannual anomalies which respond to a local mode (a purely Atlantic atmosphere-ocean feedback), and the portion of interannual anomalies which respond to a remotely forced mode (i.e., from Pacific)?
• Is there, in subsurface waters, a signature of the now established (at least for low-frequency variability) surface tropical Atlantic dipole?
• Is there a relationship (feedback?) between the low-frequency variability (decadal) of the intertropical dipole and the low-frequency variability of the thermohaline circulation in higher latitudes?
• What is the range of the northward western boundary coastal flux (North Brazil Current) and its variability?
• How can equatorial/tropical wave systems perturb/maintain climatic variability?

• What is the role of topography in the deep circulation?
• What are the spatio-temporal features of meridional circulation cells on both sides of the equator?
• Are there gradual changes in the deep water of the eastern basin? Is there a deep upwelling in the eastern basin?

• Historical data analyses (surface and subsurface observations, multi-annual simulation results, etc.)
• Five lines of XBT measurements with a thermosalinograph recording: Le Havre-Cayenne, Le Havre-Rio de Janeiro, Le Havre-Capetown, Le Havre-West Indies, Dakar-Belem.
• Hydrographic cruises with current and tracers measurements:
  1. Repetition of short sections near Cayenne; bimonthly during 18 months (SABORD program)
  2. Equatorial section plus short meridional sections every 10 degrees longitude; one section every 3-4 years.
• Moorings:
  1. Classical moorings plus ADCP near Cayenne.
  2. A "TAO-type" array along the equator (including a few deeply instrumented buoys) with possible northern and southern expansion
     • Satellite data: altimetry, wind, SST, water vapor content, etc.
     • Modelisation (entire hierarchy of models)

Collaborations. Due to the high level of personnel, material and ship requirements (particularly for the implementation and maintenance of a future Atlantic TAO array), large-scale scientific cooperation with other national and international institutes is absolutely necessary:
National (France)

• CNRS, IFREMER, CNES, Universities
• Other Atlantic-CLIVAR components (high and mid-latitudes)
• Pacific and Indian CLIVAR components
• Modelisation development groups
• Satellite data working groups

• International TAO
• US ACCE
• US PACS
• Brazilian institutes (INPE, FUNCEME, IOUSP, UFP)
• International CLIVAR
• WOCE

• Pacific Ocean observations for operational ENSO forecasts
• Coastal U.S. observations for red tides and other toxic algal blooms
• Global sea level efforts for prediction of U.S. coastal effects
• Coastal U.S. observations required for critical marine forecasts and warnings

The principal activity for U.S. GOOS for the coming year will be to host the GOOS Priority Agreements Meeting scheduled for May 1996. At the I-GOOS II meeting in June 1995 in Paris an international Priorities Working Group was commissioned to prepare an initial implementation plan for GOOS containing the recommended set of initial activities. The plan is to be distributed to governments and ocean agencies by early November, 1995 for national debates and decisions. These national decisions on GOOS contributions will then be identified and documented at the Priority Agreements Meeting in May. The implementation plan addresses all GOOS modules and is organized as follows:

1. Objectives - The need the module addresses and the priority products to be produced.
2. The status of establishment of the scientific basis for these objectives.
3. The parameters contributing to meeting the objectives.
4. The tools available - observing systems that are candidates.
5. The priority activities to be undertaken, in the categories of:
   • Ongoing, to be continued
   • Ongoing, to be expanded
   • New

TAO Data Monitoring. The NOS Observing Networks Branch, in cooperation with the NMC Coupled Model Project, has begun a project to monitor the quantity of TAO observations that are assimilated into the operational models and analyses at NMC. This project complements the ongoing monitoring of the quantity of TAO data being inserted onto GTS for international distribution. This is a new project and the monitoring has only recently begun and is currently limited to wind observations only. A full report and analysis will be provided at the next meeting of the TAO Implementation Panel.

Dr. Spence also provided a brief review of the CLIVAR program of WCRP, noting the publication of the CLIVAR Science Plan, and the establishment of modeling, process, and observation groups. He reported that an Upper Ocean Panel would consider observational needs for CLIVAR, and would, therefore, relate to the TAO Implementation Panel activities.

Finally, he briefly reviewed the international GOOS activity, and reminded the Panel that TAO remains a source of high priority observations for the climate module of GOOS (the ocean component of GCOS), and that the planned "priorities" meeting would urge continuation of TAO with international support.

He concluded by extending the continued support of GCOS and CLIVAR for the work of the Panel.

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