Global Drifter Program

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This is a snapshot of the distribution of the drifters in the GDP. (A live tracking update of drifter locations is available through Google Earth at www
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This is a snapshot of the distribution of the drifters in the GDP. (A live tracking update of drifter locations is available through Google Earth at www.aoml.noaa.gov/phod/dac/gdp_maps.php .)

The Global Drifter Program (GDP) (formerly known as the Surface Velocity Program (SVP)) was conceived by Prof. Peter Niiler, with the objective of collecting measurements of surface ocean currents, sea surface temperature and sea-level atmospheric pressure [1] using drifters. It is the principal component of the Global Surface Drifting Buoy Array, a branch of NOAA's Global Ocean Observations [2] and a scientific project of the Data Buoy Cooperation Panel (DBCP). [3] [4] The project originated in February 1979 as part of the TOGA/Equatorial Pacific Ocean Circulation Experiment (EPOCS) and the first large-scale deployment of drifters was in 1988 with the goal of mapping the tropical Pacific Ocean's surface circulation. [5] The current goal of the project is to use 1250 satellite-tracked surface drifting buoys to make accurate and globally dense in-situ observations of mixed layer currents, sea surface temperature, atmospheric pressure, winds and salinity, and to create a system to process the data. [4] Horizontal transports in the oceanic mixed layer measured by the GDP are relevant to biological and chemical processes as well as physical ones. [6]

Contents

Drifters

This is a picture of the drifters used in the GDP (photo by GDP). Drifterpic1.jpg
This is a picture of the drifters used in the GDP (photo by GDP).

SVP project drifter deployments began in 1979; the design continued to develop until reaching its current form in 1992. [5] Each drifter consists of a spherical surface buoy tethered to a weighted nylon drogue that allows it to track the horizontal motion of water at a depth of 15 meters. [6] If the drogue breaks off, the wind pushes the surface buoy through the water, creating erroneous current observations. [6] A tether strain gauge has been added to monitor tension of the buoy-drogue connection to resolve this issue. [6] The original drifters are heavy, bulky (40 cm diameter), and expensive relative to the newer "mini" drifters that are smaller, (30.5 cm diameter) cheaper, and lighter because the hull contains fewer batteries. [5] The surface float contains alkaline batteries, a satellite transmitter, a thermistor for sub-skin sea surface temperature, and sometimes other instruments that measure pressure, wind speed and direction, or salinity. [5]

SVP buoy fitted with a barometer (photo by DBi) SVP-B.jpg
SVP buoy fitted with a barometer (photo by DBi)

The drifters are deployed from research vessels, volunteer ships, and through air deployment. [5] They typically transmit their data hourly and had an average lifetime of ~485 days in 2001. [5] Presently, enough data is gathered to observe currents at a horizontal resolution of one degree (~100 km). [5] Single drifters can be tracked with the name of the drifter.

Applications

The data from the GDP have been used by oceanographers to derive maps of lateral diffusivity and Lagrangian length- and time-scales across the Pacific. [7] Other uses include studies of plastic accumulation the ocean, [8] and climatological models that simulate equatorial ocean currents, as well as many others. [9]

Nobel Laureate Desmond Tutu and Captain Jeremy Kingston deploy a drifter off of the coast of South Africa in the Semester at Sea program, where students from the Congressional School of Virginia and Elsies River High School in South Africa adopted the drifter and will be tracking its passage through the South Atlantic. Desmond Tutu deploys a drifter.jpg
Nobel Laureate Desmond Tutu and Captain Jeremy Kingston deploy a drifter off of the coast of South Africa in the Semester at Sea program, where students from the Congressional School of Virginia and Elsies River High School in South Africa adopted the drifter and will be tracking its passage through the South Atlantic.

Organization and collaborators

The GDP consists of three components. [4] The component at NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML) manages deployments, processes and archives the data, maintains META files describing each drifter deployed, develops and distributes data-based products, and updates the GDP website. [4] The Lagrangian Drifter Laboratory [11] at the Scripps Institution of Oceanography (SIO) leads the engineering aspects of the Lagrangian drifter technology, improves the existing designs, develops new drifters, manages the real-time data stream, including posting the drifter data to the Global Telecommunication System, supervises the industry, purchases and fabricates most drifters, and develops enhanced data sets. The third component is the manufacturers in private industry, who build drifters according to specifications. The GDP collaborates with partners from numerous countries including Argentina, Australia, Brazil, Canada, France, India, Italy, Republic of Korea, Mexico, New Zealand, South Africa, Spain, United Kingdom, and the United States. [4]

Related Research Articles

Buoy Floating structure or device

A buoy is a floating device that can have many purposes. It can be anchored (stationary) or allowed to drift with ocean currents.

Weather station Facility for atmospheric research and prediction

A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, atmospheric pressure, humidity, wind speed, wind direction, and precipitation amounts. Wind measurements are taken with as few other obstructions as possible, while temperature and humidity measurements are kept free from direct solar radiation, or insolation. Manual observations are taken at least once daily, while automated measurements are taken at least once an hour. Weather conditions out at sea are taken by ships and buoys, which measure slightly different meteorological quantities such as sea surface temperature (SST), wave height, and wave period. Drifting weather buoys outnumber their moored versions by a significant amount.

Physical oceanography Study of physical conditions and physical processes within the ocean

Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.

The Tropical Ocean Global Atmosphere program (TOGA) was a ten-year study (1985-1994) of the World Climate Research Programme (WCRP) aimed specifically at the prediction of climate phenomena on time scales of months to years.

Sea surface temperature Water temperature close to the oceans surface

Sea surface temperature (SST), or ocean surface temperature, is the water temperature close to the ocean's surface. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a short distance of the shore. Localized areas of heavy snow can form in bands downwind of warm water bodies within an otherwise cold air mass. Warm sea surface temperatures are known to be a cause of tropical cyclogenesis over the Earth's oceans. Tropical cyclones can also cause a cool wake, due to turbulent mixing of the upper 30 metres (100 ft) of the ocean. SST changes diurnally, like the air above it, but to a lesser degree. There is less SST variation on breezy days than on calm days. In addition, ocean currents such as the Atlantic Multidecadal Oscillation (AMO), can effect SST's on multi-decadal time scales, a major impact results from the global thermohaline circulation, which affects average SST significantly throughout most of the world's oceans.

Argo (oceanography) International oceanographic observation program

Argo is an international program that uses profiling floats to observe temperature, salinity, currents, and, recently, bio-optical properties in the Earth's oceans; it has been operational since the early 2000s. The real-time data it provides is used in climate and oceanographic research. A special research interest is to quantify the ocean heat content (OHC).

Walker circulation Theorerical model of air flow in the atmosphere

The Walker circulation, also known as the Walker cell, is a conceptual model of the air flow in the tropics in the lower atmosphere (troposphere). According to this model, parcels of air follow a closed circulation in the zonal and vertical directions. This circulation, which is roughly consistent with observations, is caused by differences in heat distribution between ocean and land. It was discovered by Gilbert Walker. In addition to motions in the zonal and vertical direction the tropical atmosphere also has considerable motion in the meridional direction as part of, for example, the Hadley Circulation.

Loop Current Ocean current between Cuba and Yucatán Peninsula

A parent to the Florida Current, the Loop Current is a warm ocean current that flows northward between Cuba and the Yucatán Peninsula, moves north into the Gulf of Mexico, loops east and south before exiting to the east through the Florida Straits and joining the Gulf Stream. The Loop Current is an extension of the western boundary current of the North Atlantic subtropical gyre. Serving as the dominant circulation feature in the Eastern Gulf of Mexico, the Loop Currents transports between 23 and 27 sverdrups and reaches maximum flow speeds of from 1.5 to 1.8 meters/second.

National Data Buoy Center

The National Data Buoy Center (NDBC) is a part of the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS). NDBC designs, develops, operates, and maintains a network of data collecting buoys and coastal stations. The NDBC is located in southern Mississippi as a tenant at the John C. Stennis Space Center, a National Aeronautics and Space Administration (NASA) facility.

The World Ocean Circulation Experiment (WOCE) was a component of the international World Climate Research Program, and aimed to establish the role of the World Ocean in the Earth's climate system. WOCE's field phase ran between 1990 and 1998, and was followed by an analysis and modeling phase that ran until 2002. When the WOCE was conceived, there were three main motivations for its creation. The first of these is the inadequate coverage of the World Ocean, specifically in the Southern Hemisphere. Data was also much more sparse during the winter months than the summer months, and there was—and still to some extent—a critical need for data covering all seasons. Secondly, the data that did exist was not initially collected for studying ocean circulation and was not well suited for model comparison. Lastly, there were concerns involving the accuracy and reliability of some measurements. The WOCE was meant to address these problems by providing new data collected in ways designed to "meet the needs of global circulation models for climate prediction."

Weather buoy Floating instrument package which collects weather and ocean data on the worlds oceans

Weather buoys are instruments which collect weather and ocean data within the world's oceans, as well as aid during emergency response to chemical spills, legal proceedings, and engineering design. Moored buoys have been in use since 1951, while drifting buoys have been used since 1979. Moored buoys are connected with the ocean bottom using either chains, nylon, or buoyant polypropylene. With the decline of the weather ship, they have taken a more primary role in measuring conditions over the open seas since the 1970s. During the 1980s and 1990s, a network of buoys in the central and eastern tropical Pacific Ocean helped study the El Niño-Southern Oscillation. Moored weather buoys range from 1.5–12 metres (5–40 ft) in diameter, while drifting buoys are smaller, with diameters of 30–40 centimetres (12–16 in). Drifting buoys are the dominant form of weather buoy in sheer number, with 1250 located worldwide. Wind data from buoys has smaller error than that from ships. There are differences in the values of sea surface temperature measurements between the two platforms as well, relating to the depth of the measurement and whether or not the water is heated by the ship which measures the quantity.

A mooring in oceanography is a collection of devices connected to a wire and anchored on the sea floor. It is the Eulerian way of measuring ocean currents, since a mooring is stationary at a fixed location. In contrast to that, the Lagrangian way measures the motion of an oceanographic drifter, the Lagrangian drifter.

Ocean heat content Thermal energy stored in ocean water

In oceanography and climatology, ocean heat content (OHC) is a term for the energy absorbed by the ocean, where it is stored for indefinite time periods as internal energy or enthalpy. The rise in OHC accounts for over 90% of Earth's excess thermal energy from global heating since year 1970. About one third of the added energy has propagated to depths below 700 meters as of 2020.

In physical oceanography and fluid dynamics, the wind stress is the shear stress exerted by the wind on the surface of large bodies of water – such as oceans, seas, estuaries and lakes. Stress is the quantity that describes the magnitude of a force that is causing a deformation of an object. Therefore, stress is defined as the force per unit area and its SI unit is the Pascal. When the deforming force acts parallel to the object's surface, this force is called a shear force and the stress it causes is called a shear stress. When wind is blowing over a water surface, the wind applies a wind force on the water surface. The wind stress is the component of this wind force that is parallel to the surface per unit area. Also, the wind stress can be described as the flux of horizontal momentum applied by the wind on the water surface. The wind stress causes a deformation of the water body whereby wind waves are generated. Also, the wind stress drives ocean currents and is therefore an important driver of the large-scale ocean circulation. The wind stress is affected by the wind speed, the shape of the wind waves and the atmospheric stratification. It is one of the components of the air–sea interaction, with others being the atmospheric pressure on the water surface, as well as the exchange of energy and mass between the water and the atmosphere.

Drifter (floating device) Oceanographic instrument package floating freely on the surface, transported by currents

A drifter is an oceanographic device floating on the surface to investigate ocean currents and other parameters like temperature or salinity. Modern drifters are typically tracked by satellite, often GPS. They are sometimes called Lagrangian drifters since the location of the measurements they make moves with the flow. A major user of drifters is the Global Drifter Program.

A self-locating datum marker buoy (SLDMB) is a drifting surface buoy designed to measure surface ocean currents. The design is based on those of the Coastal Ocean Dynamics Experiment (CODE) and Davis-style oceanographic surface drifters – National Science Foundation (NSF) funded experiments exploring ocean surface currents. The SLDMB was designed for deployment by United States Coast Guard (USCG) vessels in search and rescue (SAR) missions, and is equipped with a Global Positioning Satellite (GPS) sensor that, upon deployment in fresh- or saltwater, transmits its location periodically to the USCG to aid in SAR missions. Additionally, SLDMB are deployed in oceanographic research in order to study surface currents of the ocean. This design has also been utilized by Nomis Connectivity for secure ocean-based communications.

Pearn P. Niiler American oceanographer

Pearn "Peter" Niiler was an American oceanographer.

In oceanography, Ekman velocity – also referred as a kind of the residual ageostropic velocity as it derivates from geostrophy – is part of the total horizontal velocity (u) in the upper layer of water of the open ocean. This velocity, caused by winds blowing over the surface of the ocean, is such that the Coriolis force on this layer is balanced by the force of the wind.

The Tropical Atmosphere Ocean (TAO) project is a major international effort that instrumented the entire tropical Pacific Ocean with approximately 70 deep ocean moorings. The development of the TAO array in 1985 was motivated by the 1982-1983 El Niño event and ultimately designed for the study of year-to-year climate variations related to El Niño and the Southern Oscillation (ENSO). Led by the TAO Project Office of the Pacific Marine Environmental Laboratory (PMEL), the full array of 70 moorings was completed in 1994.

An ocean data acquisition system (ODAS) is a set of instruments deployed at sea to collect as much meteorological and oceanographic data as possible. With their sensors, these systems deliver data both on the state of the ocean itself and the surrounding lower atmosphere. The use of microelectronics and technologies with efficient energy consumption allows to increase the types and numbers of sensor deployed on a single device.

References

  1. Centurioni, Luca; et al. (2016). "A Global Ocean Observing System for Measuring Sea Level Atmospheric Pressure: Effects and Impacts on Numerical Weather Prediction". Bull. Amer. Meteor. Soc. 98 (2): 231–238. doi: 10.1175/BAMS-D-15-00080.1 .
  2. Global Ocean Observing System (GOOS)
  3. Data Buoy Cooperation Panel (DBCP)
  4. 1 2 3 4 5 "PhOD - Global Drifter Program".
  5. 1 2 3 4 5 6 7 Lumpkin, R. and M. Pazos, 2006: Measuring surface currents with Surface Velocity Program drifters: the instrument, its data, and some recent results. Chapter two of Lagrangian Analysis and Prediction of Coastal and Ocean Dynamics (LAPCOD) ed. A. Griffa, A. D. Kirwan, A. J. Mariano, T. Ozgokmen, and T. Rossby.
  6. 1 2 3 4 Grodsky, Semyon A., Rick Lumpkin, and James A. Carton. "Spurious trends in global surface drifter currents." Geophysical Research Letters 38.10 (2011).
  7. Zhurbas, Victor, and Im Sang Oh. "Lateral diffusivity and Lagrangian scales in the Pacific Ocean as derived from drifter data." Journal of Geophysical Research: Oceans (1978–2012) 108.C5 (2003).
  8. Law, Kara Lavender, et al. "Plastic accumulation in the North Atlantic subtropical gyre." Science 329.5996 (2010): 1185-1188.
  9. Large, William G., et al. "Equatorial circulation of a global ocean climate model with anisotropic horizontal viscosity." Journal of Physical Oceanography 31.2 (2001): 518-536.
  10. "PhOD - Global Drifter Program".
  11. "Lagrangian Drifter Lab". gdp.ucsd.edu. Retrieved 2017-04-07.