Basin Scale Contributions to the observing system - Working Group1

Chair: Gary Meyers
Rapporteurs: Peter Hacker,Ed Harrison

• Issues Addressed

• Working Group Report

• Basin scale Issues

• Argo
• Mooring Arrays
• Ship-of-Opportunity XBT Strategy

Issues Addressed

Working Group 1 was concerned with present and future availability of basin-scale observations and the need to develop an implementation strategy that builds on the plans developed at the SOCIO Workshop in Perth (November 2000). The Working Group was asked particularly to:

• Identify the next steps that will have impact on research progress and deliver climate services.
• Decide the mooring array required for the Indian Ocean and the strategy to implement the array in stages.
• Determine the spatial and temporal priorities for Argo deployment, based on the scientific issues of the region and develop specific Argo deployment plans (i.e., find ships that go where they are needed).
• Define the principles and guidelines for integrating the ocean, climate and coastal observing systems.

Working Group Report

Reporters : Peter Hacker, Neville Smith

Working Group 1 on Basin-scale Contributions to the Observing System proposed three pilot projects:

• to develop the deployment of Argo floats, from the present level of about 67 to 170 in 2003, and 450 in 2005
• to develop Indian Ocean mooring arrays, especially in the equatorial zone, but also in the four zones of high sea-surface temperature anomalies (northern Bay of Bengal, of the southern coasts of Sumatra and Java, western Arabian Sea, and the southern Indian Ocean)
• the implementation of a new Ship-of-Opportunity XBT Project, with emphasis on high-resolution, frequently repeated lines across the Indian Ocean. However, the other elements of the sustained integrated ocean-observing system for climate that have been identified as needed were not discussed, for lack of time.

The Argo program seeks to describe ocean temperature and salinity variability on seasonal and longer time-scales for space-scales of 1000 km and larger. The present strategy is to initiate coverage of as much of the basin as possible, even if at a reduced spatial resolution.

Regarding mooring arrays, India intends to maintain an array of about 40 surface moorings in waters north of 5° N, but details of the initial planned deployment were not made available. OOPC recommendations for sustained ocean air-sea reference-site moorings identify three Indian Ocean sites: the Arabian Sea, the Bay of Bengal, and the subduction region west of Australia toward mid-basin. The northernmost two of these three sites would clearly contribute to subseasonal-variability studies.

Several projects (see presentation by Matsumoto et al., mentioned above), in development or already funded, address various aspects of these issues: the French equatorial array near 73° E; the IMAP array, led by South Africa; an equatorial waveguide array to complete sampling of the waveguide and ISO propagation into the Bay of Bengal (USA and other countries); an ambitious array of 40 moorings north of 5° N, funded by the Department of Ocean Development (India), and for which, a mix of surface and subsurface moorings will be proposed.

Regarding the Ship-of-Opportunity Project, the advent of Argo and precision altimetry has changed the context within it operates. Line-mode sampling (high-resolution and frequently repeated lines) is expected to promote synergy with Argo, satellite altimetry, and moored arrays; there is a special utility of such sampling in boundary regions and it has a unique role in heat and freshwater transport calculations.

Basin Scale Issues

Argo

An array of about 450 floats is required to meet the Argo programme goal (describe ocean temperature and salinity variability down to 40° S, roughly the southern boundary of the Indian Ocean proper). At present there are about 67 floats deployed, but commitments have been made to have about 170 floats in the Argo array by the end of 2003 (see the presentation by Wijffels et al., mentioned above). The Working Group reaffirmed the importance of achieving full initial deployment of the Argo array in the Indian Ocean.

Dr. M Ravichandran (Scientist, INCOIS) will coordinate efforts to fill gaps and make most effective use of deployment assets. All data will be made available within 24 h of capture, via the Argo data system and the GODAE data servers.

Commitments are being sought to deploy the entire array by the end of 2005, but support to maintain the array, subsequently, will have to be found.

Because of the strong high-frequency variability in several regions, the Working Group agreed that studies should be carried out to determine whether modifications to the standard Argo sampling strategy (parking at 2000 m, profiling every 10 days) are needed. Several groups agreed to pursue this matter, making use of the few available moored-profile time-series and various numerical-ocean-model data sets.

Mooring arrays

The Working Group's discussion focused on the combination of moorings that would best address many of the recently identified issues relative to the response of the ocean and its role in determining subseasonal variability, including the Intra-seasonal Oscillation (ISO) and tropical cyclones.

Strong interest was expressed in establishing an array of moorings along and near the equator to help improve understanding and forecasting of equatorial currents, waves, and air-sea processes unique to the Indian Ocean. Understanding the role of ocean conditions and/or ocean-atmosphere coupling in the ISO will be a goal; so will exploring its predictability. If maintained for several years, this mooring array will also begin to define the seasonal variability of the equatorial waveguide.

The four distinct regions of SST anomaly (SSTA) variability in the Indian Ocean are: the northern Bay of Bengal; just off the southern coasts of Java and Sumatra; a wide area of the southern Indian Ocean; and the western Arabian Sea. SST variability in the equatorial Indian Ocean differs from that of the Pacific in that the equatorial waveguide is not the primary area of SSTA variability. There was considerable discussion of the use of moorings to understand and forecast SST variability in the mid-ocean. The primary mid-ocean region is south of the equator, with the northern edge along the thermocline ridge just south of the equator (5° -10° S), and the southern edge between 15° and 25° S. It was agreed that, at this initial stage of exploration, air-sea measurements were the key and therefore surface moorings are required.

The importance of the variability of the Indonesian Throughflow (ITF) on Indian Ocean circulation and SST was recognized. The INSTANT project seeks to establish a five-mooring array to monitor the ITF better.

The particular sites discussed were:

• 50° E at 0° N
• 60° E at 8° S, 0° N
• 65° E (instead of 60° E and 70° E ??)
• 70° E at 12° S, 8° S, 0° N
• 80° E at 8° S, 5° S, 0° N, 2.5° N, 5° N
• 88° -95° E at 5° S, 0° N, 5° N, 12° N
• 105° E at 8° S
• the INSTANT project array
• OOPC Ocean Reference Sites in the Arabian Sea, Bay of Bengal, South Indian Ocean Subduction (as well as the Kerguelen Islands site in the Southern Ocean).

However, the Working Group could not finalize the large-scale open-ocean moored-buoy array design. It did discuss additional mooring sites that in principle can address most of the scientific issues in the CLIVAR science plan. It recognized that so many sites cannot be developed in the short term, however. An ad hoc Working Group of the Tropical Moored Buoy Array Implementation Panel was formed at the close of the Working Group's meeting to pursue design issues relating to the open-ocean moored-buoy array. The Panel Chairman will seek formal recognition of the Working Group by relevant bodies (e.g., IOGOOS Development Committee, CLIVAR Scientific Steering Group). The challenge for the Working Group is to design the first steps toward a pilot sustained array.

As many sites as possible will measure surface meteorology as well as u(z) (pressure, u, at depth, z), T(z) (temperature, T, at depth, z) and S(z) (salinity, S, at depth, z). The OOPC ORS moorings are also committed to supporting the development and use of biogeochemical sensors.

The Working Group noted that the USA (Pacific Marine Environment Laboratory and Woods Hole Oceanographic Institute) and the Japanese Marine Science and Technology Center (JAMSTEC) surface measurements have recently been investigated. The comparison of TRITON and ATLAS moorings in the western Pacific Ocean showed significant agreement. Nevertheless, the Working Group considered it necessary to establish the comparability of data from all moorings that will be deployed as part of IOGOOS, although the cost and feasibility of such a comparison needs to be assessed first.

It also agreed that such moorings should conform to GOOS data policy in order to support GODAE and to increase the quality of operational-oceanography products that will be available to the nations of the Indian Ocean rim. The importance of real-time access to moored observations, in support of operational oceanography objectives, was stressed.

The Working Group noted that substantial ship time will be required to deploy and maintain mooring arrays in the Indian Ocean, making the shared use of available ships very important. Suitable ships may be available, if funding can be supplied.

The proposed moored array will be carried forward as Pilot Projects. Funding will be sought through CLIVAR as well as GOOS, depending upon national priorities. Deployment priorities will be determined by the availability and source of funding.

The Working Group agreed that all observing activities should be coordinated via the JCOMM Ocean Observations Coordination Group.

The mooring-array and the Argo pilot projects will be presented for review to the responsible ocean program steering groups and to other interested groups. In particular: Partnership for Observing the Global Oceans (POGO; Hobart, 22-24 January 2003); IOGOOS Executive Committee (at its first meeting); Asia/Australia Monsoon Panel (AAMP; Atlanta, GA, 25-27 February 2003); Ocean Observations Panel for Climate (OOPC; Ottawa, July 2003).

Ship-of-Opportunity XBT Strategy

The Working Group endorsed a new SOOP XBT sampling strategy. It was recognized that there should be a change in emphasis from broad-scale, areal sampling to line-mode sampling (high-resolution and frequently repeated lines) progressively over the next five years. This approach will promote synergy with Argo, the surface reference network, altimetry, and moored arrays. India, supported by Australia, will take the lead in establishing the new XBT sections. One will extend across the northern Arabian Sea and the other across the southern Bay of Bengal (see the extended abstract by Gopalakrishna et al. at the above-cited ftp site). There was unfinished discussion of the most appropriate combination of spatial resolution and repeat time between sections. These discussions will continue.

The utility of reporting the XBT results in real time was discussed. Development of a telecommunication enhancement to the XBT SEAS system, using IRIDIUM, which would greatly ease such communication, is well advanced. The Working Group considered that coordination via the JCOMM Ship Operations Team was appropriate.

The sessional Working Group also identified a number of actions on which there is a real, remaining need for further discussion:

• The plan to provide the sustained observations required to meet the relevant objectives identified by CLIVAR, GOOS and GCOS include: surface-climate-quality basin-wide SST, surface-wind and sea-surface-height fields and surface reference sites; upper ocean-seasonal and longer-time-scale temperature and salinity fields and certain boundary-current-flow information; water column-decadal-time-scale basin changes in the carbon inventory and carbon distribution, nutrients and tracers and flows over certain sills and off certain shelves.
• Integration of satellite and in situ observations.

The Working Group considered that IOGOOS should work toward deployment, maintenance, and sustainability of these observing activities, as well as to carry forward the pilot projects identified above.

Participation of IOGOOS countries in the international GODAE also requires further discussion. Use of GODAE products and other operational ocean products to meet the coastal and climate needs of IOGOOS nations, including feedback to GODAE participants on how to improve GODAE products and services, should be encouraged.