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Facilitating Access to Global Observing Systems Data and Information

GCOS Ocean Surface ECV
Current

Definition: A movement of ocean water characterized by regularity, either of a cyclic nature or, more commonly, as a continuous stream flowing along a definable path. Three general classes, by cause, may be distinguished: 1) currents related to seawater density gradients, comprising the various types of gradient current; 2) wind-driven currents, which are those directly produced by the stress exerted by the wind upon the ocean surface; and 3) currents produced by long-wave motions. The latter are principally tidal currents, but may include currents associated with internal waves, tsunamis, and seiches. The major ocean currents are of continuous, stream-flow character, and are of first-order importance in the maintenance of the earth's thermodynamic balance. (From the Glossary of Meteorology)

Introduction: The global surface current field is primarily relevant to climate through its role in the heat, freshwater and carbon transport, and the shallow overturning ocean circulation. Research also suggests a role in determining air-sea exchanges of momentum (wind stress).  Derived analyses of the global surface current field, based primarily on dynamical models, surface wind and sea-level data, are feasible.  
 
Contributing networks and satellite observations include:

  1. Drifting buoys.
  2.  Global tropical moored buoy network.
  3.  Ship drift.
  4.  Satellite AVHRR (pattern tracking).
  5.  Satellite altimetry (geostrophic).
  6.  Analysis – blended estimates.
  7.  Assimilation (indirect) as in GODAE.

Issues relative to surface current observation and analysis include:

  1. The in situ and shore-based networks do not provide global coverage or sampling relative to the required space and time scales. 
  2.  Drifting buoys have uneven drift characteristics (drogues) and no agreed standard.
  3.  There is no designated centre for current data exchange, product assembly, quality control and archiving, or other group performing these functions in research mode.
  4.  Indirect estimates, including those with models (e.g., by GODAE), are data limited and subject to model biases. Lack of validation data limits ability to estimate uncertainties.  However, such approaches provide the only long-term viable approach.

To address the issues raised above, it is proposed that OOPC work with JCOMM and WCRP to identify a group of persons and/or organizations willing to establish a programme to collect surface drifting buoy motions, ship drift current estimates and to make global estimates of current based on wind stress and surface topography fields.  

(Source: WMO/IOC Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (2010 Update) GCOS-138/GOOS-184/GTOS-76/WMO-TD/No. 1523)

Satellite Observations: (Satellite Missions)

Additional Information:

References:

Data, Product, Metadata and Information Access

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Non-satellite or in situ Satellite