Moorings

Moorings are capable of measuring some of the key variables needed to describe, understand and predict large-scale ocean dynamics and ocean-atmosphere interactions. Marine meteorological variables include those needed to characterize fluxes of momentum, heat and fresh water across the air-sea interface, namely, surface winds, SST, air temperature, relative humidity, downward short and long-wave radiation, barometric pressure and precipitation. Physical oceanographic variables include upper-ocean temperature, salinity and horizontal currents. From these basic variables, derived quantities, such as latent and sensible heat, net surface radiation, penetrative shortwave radiation, mixed-layer depth, ocean density, and dynamic height (the baroclinic component of sea level) can be computed. The array design focuses on these marine meteorological and physical oceanographic variables, though not all moorings will measure all variables. The moorings can also support sensors to measure CO2 concentrations in air and sea water, nutrients, bio-optical properties and ocean acoustics (International Clivar Project Office 2006).

The Global Tropical Moored Buoy Array (GTMBA) is a multi-national effort to provide meteorological and ocean observational data in real-time for climate research and forecasting (McPhaden et al. 2009a). The buoys are used to collect oceanographic and meteorological data for monitoring forecasting, and climate research, particularly for ENSO studies. The array consists of the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON) in the Pacific, the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA), and the Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (RAMA) in the Indian Ocean. These observing systems were designed and implemented within the framework of GOOS and GCOS. The primary objectives are to study intraseasonal to decadal time scales including ENSO and the Pacific Decadal Oscillation (PDO) in the Pacific, the meridional gradient mode and equatorial warm events in the Atlantic, the IOD and the Mad-den-Julian Oscillation (MJO) in the Indian Ocean, the mean seasonal cycle, including the Asian, African, Australian, and American monsoons and trends in all three basins that may be related to global warming. However, these observations will complement other in-situ and satellite observational components of Global observing systems.

The GTMBA is built primarily around the Autonomous Temperature Line Acquisition System (ATLAS) moorings of NOAA's Pacific Marine Environmental Laboratory (PMEL) and TRITON moorings of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). The Schematic diagram of the ATLAS moorings with the locations of different sensors fitted on the buoys and on the moorings is available in PMEL website. These moorings have special attributes that make them a valuable technology for tropical climate studies. In particular, (1) they can be instrumented to measure both upper ocean and surface meteorological variables involved in ocean-atmosphere interactions; (2) they provide time series measurements at fine temporal resolution (minutes to hours) to resolve high frequency oceanic and atmospheric fluctuations that would otherwise be aliased into the lower frequency climate signals of primary interest; (3) they can be deployed and maintained on a fixed grid of stations, so that measurements do not distort the variability in time and space. The data from surface moorings are transmitted to shore via ARGOS satellite in real-time, which ensures (a) use of these data for operational weather, Ocean, and climate forecasting and (b) retrieval of data even if a mooring is lost. The data are posted daily and made freely available on the NOAA/Pacific Marine Environmental Laboratory GTMBA web site (http://www. pmel.noaa.gov/tao/global/global.html) as well as several web sites maintained by partner institutions around the world. Service Argos inserts the data on the GTS several times a day. Details about different types of moorings used in the GTMBA, including subsurface ADCP and deep ocean moorings, can be found in McPhaden et al. (2009a). Mooring sensor specifications (accuracy, resolution, range), sensor calibration procedures, and data quality control for both real-time and delayed

Global Tropical Moored Buoy Array TRITON TAO ■

J ^ RAMA ° ^Hl^ "nf;rf - Cprrating Open = Planne^^^^ PIRATA ^^ 60°E 120°E 180° 120°W 60°W 0°E

■ Standard Mooring

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Enhanced

■ Flux Reference Site

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and Bio-Chem Enhanced

■ Flux and C02 Enhanced

Fig. 3.5 The Global tropical moored buoy array in October 2009. (Source: McPhaden et al. 2009a)

Fig. 3.5 The Global tropical moored buoy array in October 2009. (Source: McPhaden et al. 2009a)

mode data streams are available from websites maintained by PMEL and JAM-STEC website. The present status of GTMBA array in the Global ocean is shown in Fig. 3.5.

TAO/TRITON data have been used in over 600 refereed journal publications since its inception in 1985. TAO/TRITON has been the dominant source of upper ocean temperature data near the equator over the past 25 years. The data show that depth average temperature in the upper 300 m, an index for upper ocean heat content, leads Niño3.4 SST (area-average SST anomalies between 5°N-5°S and 170°-120°W) typically by 1-3 seasons. A build up of heat content at the end of this record, followed by rising Niño3.4 SSTs, indicates development of the current 2009 El Niño event. This relationship between upper ocean heat content and SST not only validates recharge oscillator theory, but also highlights the role of heat content as the primary source of predictability for ENSO. The simple relationship has motivated the inclusion of upper ocean heat content as a predictor in some statistical ENSO forecast models (e.g., Clarke and van Gorder 2003; McPhaden et al. 2006), analogous to the assimilation of upper ocean temperature in dynamical ENSO forecast models (e.g., Latif et al. 1998). PIRATA data have been very influential in identifying the causes of the observed SST variations in the tropical north Atlantic over the past 10 years (McPhaden 2008). Year-to-year swings in tropical north Atlantic SST appear to be principally related to wind-evaporation-SST feedbacks (Chang et al. 2001) with contributions from shortwave radiation and horizontal advection.

RAMA, even in the initial stages of development, is providing valuable data for describing and understanding variability in the Indian Ocean. For example, a pronounced semiannual cycle in upper-ocean temperature, salinity, and zonal velocity is evident in the first three years of data from near-equatorial moorings at 90°E (Hase et al. 2008). The semi-annual velocity variations are referred to as Wyrtki Jets and their zonal mass transports are largely governed by wind-forced linear dynamics (Nagura and McPhaden 2008). They are also strongly modulated on 30-50 day intraseasonal time scales related to the MJO (Masumoto et al.

2005). Variations in meridional velocity on the equator in contrast are dominated by higher frequency 10-20 day period oscillations, which are evident not only in the upper 400 m but also at depths greater than 2,000 m (Murty et al. 2006; Ogata et al. 2008). Sengupta et al. (2004) identified these oscillations as wind forced mixed Rossby-gravity waves. RAMA data indicate that subsurface temperature variations lead those at the surface by a season near the equator in eastern basin, suggesting that upper ocean thermal structure may be a source of predictability for the IOD as in the Pacific for ENSO (Horii et al. 2008). Moored buoy data are routinely used in ocean state estimation, operational ocean analyses, operational atmospheric analyses and reanalyses. These data have also been used extensively for model validation, and for satellite validation of surface winds, SST, rainfall, and shortwave radiation.

Further, in order to build and maintain a multidisciplinary global network for a broad range of research and operational applications, the new program "OceanS-ITES" is evolving (Send et al. 2009). The OceanSITES program is the global network of open-ocean sustained time-series measurements, called ocean reference stations, being implemented by an international partnership of researchers. OceanSITES provides fixed-point time series of various physical, biogeochemical, and atmospheric variables at different locations around the globe, from the atmosphere and sea surface to the seafloor. OceanSITES moorings are an integral part of the Global Ocean Observing System. They complement satellite and other in-situ data by adding the dimensions of time and depth. All OceanSITES data are publicly available. More information about the project is available at http://www.oceansites.org.

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