World Ocean Circulation Experiment
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WORLD OCEAN CIRCULATION
WOCE Data Guide 1997
Available as pdf
Note: Due to the publication date of this document, some of the hyperlinks contained within may be out of date and may not work.
What is WOCE?
The World Ocean Circulation Experiment is the part of the World Climate Research Programme that will provide much-needed improvements in ocean circulation models for use in climate prediction. The oceans are a key element in the climate system in the way they transport heat and fresh water and exchange these with the atmosphere. The oceans also sequester CO2 released by the burning of fossil fuels. WOCE has used resources from 25 countries to make unprecedented in-situ and satellite observations of the global ocean between 1990 and 1997 and to observe poorly-understood but important physical processes. In parallel, great advances have been made during WOCE in the ability of ocean models to reproduce the known characteristics of the ocean and its circulation. Analysis, Interpretation, Modelling and Synthesis of WOCE data (WOCE AIMS) will continue to 2002 but a prerequisite for its success will be the continuing assembly and quality control of WOCE data. The diverse WOCE data sets will serve as a unique resource for climate researchers and marine scientists for decades to come.
WOCE Data and Information System
The WOCE data management structure is a distributed system which utilises the expertise of scientists in order to attain the highest possible data quality and documentation. Each measurement technique produces a different data "stream", and the data management system brings them together to form a single data resource for numerous investigators and analysis groups. The system consists of several elements with the flow being from Principal Investigator to DAC to SAC to users and Archive.
Data Assembly Centers (DACs) are managed by scientists, handle assembly and quality control of data sets, and generate data products.
Special Analysis Centers (SACs) perform data analysis and synthesis functions, including the generation of derived data sets.
WOCE Archive is distributed across the Centers of the World Data Center System.
The Data Information Unit (DIU) is a central source of information on the status of WOCE, tracking all data collection, processing and archiving activities, and acting as the primary interface between the WOCE data system and all users.
Navigation through the Web http://www.wocediu.org/
This document provides a basic outline of the WOCE data system but for detailed information the user should contact the DIU, and for access to data sets contact the DACs and SACs themselves. A suggested route is to start a World Wide Web tour at the DIU where summaries of the field programme and data status are continually updated. Links exist to all components of the WOCE data system, to further data sources which may be of interest, and to a bibliography of WOCE references. If you do not have access to the Internet, contact the DIU (see back cover) for information on other means of accessing data.
Sharing WOCE Data
WOCE has developed a data sharing policy which strikes a balance between the requirements of the experiment as a whole and the intellectual rights of the individuals who contribute to the programme. The trade-off between these different interests has resulted in a policy which expects data to be made publicly available within 2 years of the data set being complete. Investigators are thus allowed a reasonable period to complete their own analysis and publications, while ensuring the global dataset is accumulated and made accessible for wider examination. Data will not be released by the data Centers without the consent of the originator. WOCE encourages investigators to share data with others and to authorise general release as soon as possible. If investigators demand exclusive rights to data more than 2 years old then WOCE encourages peer pressure and funding agencies to persuade the originator to give consent.
WOCE HYDROGRAPHIC PROGRAMME
The WOCE Hydrographic Programme (WHP) One-Time Survey encompasses a range of physical and chemical measurements at discrete stations and from continuous sampling. Station data consist of profiles of temperature, salinity, dissolved oxygen and other parameters. Large and small volume bottle samples enable a variety of chemical properties to be analysed, including nutrients, CO2, CFCs, tritium, helium and other tracers. Most parameters are analysed on board (ship-based) but some require analysis in laboratories on land (shore-based). The WHP data submission schedule requires that ship-based data are sent to the WHP Office (DAC) 6 months after a cruise, while a further 12 months are allowed for shore-based tracer data. Data are examined by independent Data Quality Experts in order to ensure the quality of the datasets. Ship-based data are scheduled to be made available for public release up to 2 years after cruise completion. While shore-based data from cruises prior to 1994 should be available now, in fact few have been released by the PIs, and the non-availability of these data is a concern currently being addressed.
WHP Office and DAC
The repeated sections and time series stations provide information on the temporal variability of the ocean from several occupations in different seasons and years. The data from each occupation are considered separately in the data management system, thus early data from a section may be available before all the planned occupations have occurred. The map shows the sections for which at least some data have been made available or are at the WHP Office (DAC), and those for which all data remain with the Principal Investigators.
WHP Special Analysis Center
The WHP Special Analysis Center (SAC) is the final stage in the hydrographic data management process; it provides a globally consistent data set and generates dynamical products for use in models and other analyses. Specialised visualisation programs and historical (pre-WOCE) hydrographic data are also available from the SAC.
WHP Special Analysis
Center ** http://www.dkrz.de/~u241046/SACserver/SACHome.htm
High quality along-track bathymetry data from WOCE cruises are assembled at the National Geophysical Data Center, an international facility for marine geological and geophysical data management. Data are available immediately they are received by the DAC, and can be accessed via the Internet or by CD-ROM.
Bathymetry DAC **
DIRECT CURRENT MEASUREMENTS
Current Meter Moorings
High quality and uniformly processed pre-WOCE and WOCE current meter records are available from the Current Meter DAC and can be downloaded from the online database over the Internet. Data are supplied to the DAC by the PIs, but are not released to the public domain until at least 2 years after recovery and permission has been given by the PI. Edited and original records from WOCE experiments are available along with data reports and flow statistics. Users can search the online database by a variety of criteria such as geographical location or experiment name.
Current Meter DAC
A variety of acoustically- or satellite-tracked, neutrally buoyant subsurface floats have been released during WOCE. The Subsurface Float DAC is assembling these (and historical data) to form a consolidated float data set for incorporation into ocean models and climatologies. Data received by the DAC are checked, archived and made available (with PI permission) through the DAC Web site. More data are available by direct contact and joint investigations with the PIs.
Surface Drifting Buoys
Drifting buoys provide surface velocity measurements for validation of models and ground truth sea surface temperature data to initialize the ocean component of climate prediction models. Some buoys also measure atmospheric pressure. The Drifter DAC assembles and provides uniform quality data from WOCE drifting buoys and WOCE quality buoys released under other programmes. Data files and products such as track plots, mean velocity and temperature fields are available within a month of collection (no proprietary period).
Surface Drifter DAC
Acoustic Doppler Current Profilers
Shipboard acoustic Doppler current profilers (ADCPs) when used in conjunction with reliable heading and navigation data can determine absolute currents in the upper ocean. Many WOCE hydrography cruises include the collection and processing of underway ADCP data, and the DAC assembles, reviews, documents, archives and distributes these data. The DAC is a joint effort between the Japan Oceanographic Data Center (JODC) and University of Hawaii (UH). Data are available in two forms, the densely sampled set or an ASCII standard subset. The map shows the location of WOCE data currently held by the DAC; many other data sets still reside with the PIs and will eventually be submitted.
ADCP DAC **
ADCP CO-DAC **
UPPER OCEAN AND SEA SURFACE OBSERVATIONS
Upper Ocean Thermal Data
A global network of commercial ships takes voluntary upper ocean thermal measurements using Expendable Bathythermographs (XBTs) which are launched every few hours while the ship is steaming. XBTs are also deployed by fishing and research vessels, and together these observations form a global data set of temperature (and sometime salinity) profiles in the top 750 m. Some data are transmitted from the vessels to data Centers by satellites in real time (less than 30 days) and made available to users with no restriction. Higher resolution profiles are submitted to the DACs and made available to users 1 year or more after collection. Other instrumentation such as moored buoys, thermistor chains on drifting buoys, profiling floats and CTDs provide additional profiles.
Some XBT sections are occupied quarterly at a higher rate of spatial sampling. These High Density sections can determine the mean, seasonal cycle, and eddy statistics of temperature and geostrophic shear and transport fields, and obtain some measure of interannual variability. Unlike the majority of XBT data, High Density sections are maintained by PIs who submit a subset of the data in real-time, but have a 2-year proprietary period for the full dataset.
The Upper Ocean Thermal DAC consists of several Centers which together provide a globally consistent data set as part of the Global Temperature-Salinity Pilot Project (GTSPP). There are two levels of quality control available to users; batch consistency checks performed by national data Centers (US NODC and MEDS, Canada), and scientific quality control on a profile-by-profile basis performed by 3 regional Centers. The data can be accessed from US NODC which acts as the GTSPP distribution facility.
UOT DAC **
UOT DAC Participating
Assembly and Distribution
Sea Surface Salinity
Underway sea surface salinity data are collected on WHP cruises and voluntary observing ships using thermosalinographs and buckets. Processed and calibrated data are assembled and made available by the DAC. Most of the DAC holdings at present are from the ORSTOM network of voluntary observing ships; many data sets from WHP cruises still reside with the PIs.
Sea Surface Salinity
Surface Meteorological Data and Surface Fluxes
Surface meteorological data are collected on many WOCE cruises, and range from high quality near-continuous recording systems, to ship bridge observations. These data are collected, checked, archived and distributed by the Surface Meteorological DAC. The map shows the data assembled so far, but data from many other WHP cruises still reside with the PIs.
Associated with the DAC is the WOCE SAC for surface fluxes. The SAC produces regularly gridded fields of ocean surface forcing fields (e.g. winds, temperatures, humidity, turbulent fluxes of momentum, moisture, and heat) suitable for use by ocean models and intensive diagnostic studies.
At the very heart of WOCE are the global measurements made by satellites. The primary interest for WOCE lies with satellite altimetry and its associated geophysical variables of sea level variability and wave height. There are 3 altimeters operating today, the French and USA satellite TOPEX/POSEIDON (since August 1992), and the European Space Agency satellites ERS-1 (since late 1991) and ERS-2 (since April 1995). In addition the US GEOSAT mission operated just prior to the WOCE field programme. Also of interest are wind speed from scatterometers (the NASA scatterometer NSCAT, and ERS-1 and ERS-2), sea surface temperature (the USA AVHRR or Advance Very High Resolution Radiometer) and water vapour content (TOPEX/POSEIDON and the US Special Sensor Microwave Imager or SSMI).
Satellite data are managed by a variety of agencies and data Centers, so there are no WOCE satellite DACs. However data and products are available to users through the Internet. TOPEX/POSEIDON data are in the public domain and not restricted, and while ERS-1 and ERS-2 data are available only to specificied investigators, products from them are not restricted and are distributed on CD-ROM or Exabyte tape. The Internet sites listed opposite offer a variety of high-level products including corrected and quality-controlled data and anomaly fields. They also contain high-quality images and discussion of the instrumentation and products available.
Satellite Data and
Product Centers Altimetry, sea level, waveheight, scatterometry,
level, waveheight ** http://alti.cnes.fr
level, waveheight, scatterometry,
ERS-1 and ERS-2
products and programme description ** http://www.esrin.esa.it/
IN SITU SEA LEVEL DATA
WOCE tide gauges make hourly or more frequent observations to provide in situ data to support altimetry, and to estimate geostrophic currents across straits. Many stations transmit data by satellite in real time (delay of 1-3 months) and these are assembled and distributed by the Fast Delivery DAC. The Delayed Mode Sea Level DAC assembles, quality controls, distributes and archives all available sea level data (18-24 months).
Sea Level DAC
Delayed Mode Delivery
During WOCE there has been extraordinary development in the capability of numerical models to simulate the ocean's dynamical structure and properties. Both basinwide and global models show impressive realism, using 20-60 vertical levels and horizontal resolutions as fine as 1/6 of a degree. Global eddy resolving models and coupled ocean-atmosphere (climate) models require the most powerful computers and so are run at only a few Centers. New model developments (isopycnal, topography following and finite element) have diversified modelling opportunities. Assimilating WOCE observations into ocean models is a burgeoning field. Where observed winds, or satellite altimeter data or XBT measurements are introduced, models are quite successful in predicting aspects of observed ocean behaviour.
It is not possible to identify the activity of all ocean modelling groups at perhaps 100 sites around the world, but the largest have WWW sites which describe their research and also offer model output.
Model results illustrating the dynamics of the topographic impact in the Kuroshio Extension region just east of Japan. Mean abyssal currents overlaying the bottom topography. Source: H. Hurlburt, NRL, Stennis Space Center, USA.
THE WOCE DATA ARCHIVE
The secure final archive of the WOCE data set is to be carried out by the World Data Center, specifically WDC-A (Oceanography) at the National Oceanographic Data Center in the USA. WDC-A is committed to archiving and preserving the (non-satellite) WOCE data set in its entirety. In addition, all DACs and SACs are committed to producing CD-ROMs of their complete holdings to be distributed in association with WDC-A. A searchable data retrieval system will be developed at WDC-A for the WOCE data set. The Archive will provide continuity into the future when the WOCE DACs and SACs are no longer active.
WOCE Archive ** http://www.nodc.noaa.gov/
WOCE: THE LARGEST GLOBAL OCEAN EXPERIMENT SO FAR
The various components of WOCE combine to form the biggest and most comprehensive oceanographic experiment undertaken to date. Satellite measurements, in situ observations and the development of models are all contributing to this first truly global ocean experiment. The chart shows how the number of WOCE oceanographic stations far exceeds previous experiments, and illustrates the high number of "data years" of direct current measurements being accumulated. In addition there are some 60,000 XBT profiles collected per year, and extensive sets of ADCP and surface salinity data. The global satellite data sets provide a level of coverage previously unobtainable. The accurate and quasisynoptic WOCE data set will be the definitive baseline of the "state of the ocean" against which future changes will be measured. The success of WOCE has relied on a new level of international co-operation which is set to continue in future climate-related projects and global ocean observational programmes.
Project Office ** http://www.woce.org
WOCE Data Information
Unit ** http://www.wocediu.org/
WOCE Report No. 150/97,