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TAO TIP 7 Program status reports

PROGRAM STATUS REPORTS

4.1 PIRATA Status Report (J. Servain, IRD/ORSTOM, Brest)
The Pilot Research Moored Array in the Tropical Atlantic (PIRATA) is an extension of the TAO Array in the Atlantic. Twelve ATLAS moorings will be deployed during 1997-2000 as part of a multinational effort involving Brazil, France and United States (Fig. 6). Like TAO, PIRATA is designed to monitor surface meteorological variables and upper ocean thermal structure at key locations in the tropical Atlantic, with data transmitted to shore in real-time via satellite (Service Argos). These key locations are chosen to obtain information on the two main modes of seasonal-to-interannual and longer time scale variability which occur in the tropical Atlantic, i.e., the El Niño-like equatorial mode and the meridional "dipole" mode (Servain et al., 1998). PIRATA data are available to all interested users from the research or operational communities in the Web sites www.pmel.noaa.gov/pirata and www.ifremer.fr/ird/pirata/pirataus.html.

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Five deployments were made during the first phase of PIRATA experiment (late 1997 to early 1998) (see Fig. 6). One mooring failed after two months (0°N, 10°W). Therefore, an additional deployment was made at 0°N, 0°W, which also failed after 10 months. These losses, both along the equator in the Gulf of Guinea, were due to vandalism associated with tuna fisheries. Vandalism issues were discussed during the PIRATA-5 meeting (held in Abidjan just before the TIP-7 meeting) and the idea of a United Nations resolution to help mitigate against vandalism was proposed (see Appendix 1).

At the time of TIP-7 (November 1998), the PIRATA array was operational as follows:

  • Gavotte (10°S, 10°W) maintained by R/V ANTEA (IRD) in October 1998
  • Soul (0°N, 0°W) maintained byR/V ANTEA (IRD) in November 1998
  • Reggae (15°N, 38°W) deployed by R/V ANTARES (DHN) in February 1998
  • Lambada (8°N, 38°W) deployed by R/V ANTARES (DHN) in February 1998
  • Samba (0°N, 35°W) deployed by R/V ANTARES (DHN) in February 1998

The second and third (final) deployment phases are scheduled in early 1999 (by the R/V ANTEA and R/V ANTARES), and in July 1999 (by the R/V ANTEA) respectively. Intensive air-sea flux measurements are planned with an instrumented masts aboard the R/V LA THALASSA in summer 1999 during the French EQUALANT-99 experiment, from Salvador de Bahia, Brazil, to Abidjan, Cote d'Ivoire. These meteorological measurements, especially those which will be made in the vicinity of three PIRATA equatorial sites (one in the western basin, two others in the eastern basin), will be useful for calibrating turbulent air-sea fluxes estimated from the PIRATA observations via the bulk formula. During EQUALANT-99, a complex current measurement system (internally recorded data only) will be deployed close to 0°N, 10°W (Java), with an ADCP (0-250 m), a "Yoyo" system (150-1000 m daily current profiles), and conventional current measurements (1000-4000 m). An ADCP mooring (with 0-300 m measurements) is also scheduled for deployment by Brazil at the PIRATA Jazz site (0°N, 20°W) in mid-1999, as well as a meteorological buoy at 0°N, 44°W. Complementing these in-situ observations, tide-gauge data on islands located close to the equator (St Peter and St Paul Rocks, Atol das Rocas, Sao Tome) will provide information about sea level variability. Thus, a complete integrated ocean observing system (full PIRATA array, current measurements, sea level data, and meteorological observations) will be operational for at least one year (mid-1999 to mid-2000).

It is expected that at the end of the pilot phase of PIRATA (late 2000 to early 2001), other nations may join in the maintenance and possible expansion of the array (and other types of in-situ oceanic observations) to constitute a tropical Atlantic Ocean Observing System. A meeting is now scheduled in Miami for May 1999 to discuss that possibility.

Reference:
Servain, J., A.J. Busalacchi, M.J. McPhaden, A.D. Moura, G. Reverdin, M. Vianna, and S.E. Zebiak (1998): A pilot research moored array in the tropical Atlantic (PIRATA). Bull. Am. Met. Soc., 79, 2019-2031.

4.2 Tropical Rainfall Measuring Mission (TRMM) Program Status Report (T. Rickenbach, NASA/Goddard Space Flight Center)

The Tropical Rainfall Measuring Mission (TRMM) is a joint program between the National Air and Space Administration (NASA, USA) and the National Space Development Agency (NASDA, Japan) to provide unprecedented, high resolution precipitation measurements over the global Tropics. The fundamental goal of TRMM is to produce four-dimensional estimates of the vertical profile of latent heating in the tropical atmosphere. This will greatly enhance our ability to model the interaction between convective scale processes (which produce rainfall) and global circulation patterns. The TRMM satellite was launched successfully from Tanegashima Space Center, Japan on 27 November 1997.

TRMM has three main components: satellite measurements, ground validation, and field campaigns. Monthly 5o rainfall maps are the end product of the satellite measurements, provided by the Precipitation Radar (PR), the TRMM Microwave Imager (TMI), and the Visible and Infrared Radiometer System (VIRS). The PR and TMI also measure the vertical structure of precipitating systems. Coincident data from the VIRS, which measures the cloud top temperature and albedo, may be compared to the more physically direct measurements of the PR and TMI to improve ongoing climatological estimates of global rainfall from geostationary satellites. TRMM data has been approved for public release on September 1, 1998. Agreement to within 25% in global rainfall estimates was found among the different instruments on TRMM.

The ground validation (GV) component provides an independent estimate of precipitation at ten tropical GV sites, derived from surface-based radars, rain gages, and disdrometers. Radar reflectivity fields are partitioned into convective and stratiform components (as is done with the PR data), which are regions of distinct vertical heating profiles. High resolution vertical structure information is also given by the GV radars. The four primary GV sites are located at Darwin (Australia), Kwajalein (Republic of the Marshall Islands), Houston (Texas, USA), and Melbourne (Florida, USA).

The TRMM field campaigns provide extensive measurements by ground based and airborne radar, rain gages, soundings, and profilers at key locations in the tropics during the mission. The main purpose of the TRMM field campaigns is to obtain vertical profiles of latent heating (through divergence measurements from radiosondes and profilers) at several tropical land and oceanic sites. In addition, Doppler-derived vertical motion fields will assess the performance of GV and satellite convective - stratiform partitioning algorithms. Preliminary campaigns have been carried out as part of the South China Sea Monsoon Experiment (SCSMEX) and the Texas-Florida Underflights (TEFLUN) program earlier this year. The main TRMM field campaigns (one land and one ocean) will occur in early and mid 1999. The LBA-TRMM campaign will be held in Rondonia, Brazil, in the Amazon region. The Kwajalein Experiment (KWAJEX) will take place at Kwajalein Atoll in the central Pacific Ocean.

4.3 Recent Developments Relevant to TAO at Meetings of the CLIVAR Upper Ocean Panel and U.S. CLIVAR Scientific Steering Committee (W.S. Kessler, NOAA/PMEL)

The CLIVAR Upper Ocean Panel (UOP) met in Toulouse in April 1998. The major new development is the prospect of a global array of profiling floats (PALACE) that are likely to be deployed over the next few years (the array is known as ARGO, the Array for Geostrophic Oceanography). The plan is for roughly 3,000 floats making biweekly profiles of T(z) and S(z) globally. It is likely that the tropical-subtropical Pacific will be one of the early areas of concentration. This program has a large constituency, especially driven by the satellite community which is seeking to better interpret altimeter data in the light of subsurface information. Also involved are groups that assimilate XBT profiles for forecast initialization. A third community is looking at decadal modulation of the ENSO cycle and would like to study the processes of the subtropical cells and shallow overturning circulation in the Pacific.

The TAO array is well-positioned with respect to ARGO for two reasons. First, the excellent time resolution of TAO is invaluable for estimation of unsampled variability in the tropics; second, ARGO cannot properly sample the vital boundary current and equatorial regimes because of float motion. The ARGO concept works best where the floats stay put and act as virtual moorings; that is, where the flows at 1500m are weak. PALACE floats in the equatorial Pacific tend to move thousands of km, and therefore cannot be relied upon to provide a near-grid-like sampling pattern.

The UOP also had extensive discussion of salinity observations, and there is widespread agreement that subsurface salinity is a necessary parameter for interpretation and assimilation. Extensive effort is going into developing longterm salinity sensors, and we can expect cross-fertilization with similiar TAO work. The UOP also encourages and endorses the TAO subsurface salinity program.

The U.S. CLIVAR Scientific Steering Committee (SSC) met in Washington in September 1998. SSC actions are of direct relevance only to U.S. funding decisions, but will probably be influential in determining the future evolution of the TAO array and PIRATA.

The SSC recommends as U.S. CLIVAR focii (among other things):

  • The U.S. should continue to strongly support research and monitoring for ENSO prediction, and expand this effort to the decadal modulation of the ENSO cycle. For TAO, this means that the U.S. is committed to continuing support of TAO, and that U.S. work in the Pacific will extend through both subtropical gyres.
  • The SSC also recommended that the U.S. should take a major interest in Atlantic climate variability, especially tropical Atlantic interannual variability. Therefore, PIRATA will probably continue to be supported as a key element of this effort beyond the pilot program. There will also likely be support for additional U.S. observational (ocean+atmosphere) efforts in the Atlantic.
  • Data assimilation is seen as crucial to gaining the full benefit from observations. To some extent, the usefulness of observing systems will be judged on the basis of their impact on assimilation.

The SSC will note the need to study sampling strategies of the various elements of the observing system, including TAO. Refinement and evolutionary improvement of the elements of the observing system will be promoted.

4.4 Progress with the Global Ocean Observing System (GOOS)
(Janice Trotte, IOC/UNESCO)

A presentation on the basic principles and recent developments of GOOS was made, on behalf of the GOOS Project Office, one of the Tropical Atmosphere Ocean Array (TAO) co-sponsors.

GOOS is a global project co-sponsored by IOC, WMO, UNEP and ICSU. It is supported by governments and implemented according to a set of principles to which all participants adhere. There is no single model to follow and its implementation is to be fully based on the regional approach. Individual countries are free to participate, provided they accept those principles and their proposed activities fit in the GOOS Agenda.

The Capacity Building component is highly important to promote GOOS in developing States, some of them located in the African continent, and which present some level of diversity in terms of the available logistic, operational and human resources to carry out the required GOOS tasks.

Several examples of benefits in participating in GOOS were also presented, such as the laying of the foundations for the creation of an early warning storm surge system, ships meteorological routing, management of ports and harbors, forecasting of sea ice, climate forecasts, preparing for epidemics, etc. The examples provided suggest that the benefits of GOOS outweigh its costs and show how governments and society as a whole could benefit from the utilization of operational oceanographic data.

Demonstrations of how much natural forcings can impact on the economics and social welfare of coastal nations were presented, with emphasis of the use of ENSO forecasting on planning crop production. Examples of the use of operational data for forecasting malaria epidemics in Columbia and maize yield in Zimbabwe were also shown.

GOOS will capitalize on the already existing observing activities in the world's oceans, converting them into products of beneficial use by society and governments, to the extent possible. Initiatives such as the TAO array and the Pilot Research Moored Array in the Tropical Atlantic (PIRATA) are essential components of GOOS.

No one country or agency could perform the whole suite of activities required to permanently observe the state of the oceans, GOOS involve concerted actions between all observing systems, satellite agencies, existing strategies, and others, for the benefit of all potential users of GOOS products.

The GOOS Web site (http://ioc.unesco.org/goos/goos.htm) is a useful source of information on GOOS and links to related sites.

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