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Tracking Drifter Buoys
1. Introduction - Measuring Surface Circulation

Expedition Menu

1. Introduction
2. Tracking Drifters
3. Drifters Pacific
4. Drifters Atlantic
5. Drifters Indian
6. Velocity Pacific
7. Velocity Atlantic
8. Velocity Indian
9. Global Circulation
10. Counter Currents
11. Boundary Currents

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In today's expedition, you will be looking at the flow of the surfce waters of the ocean, called surface circulation, by tracking surface buoys with satellites in the major oceans.

Once again, you will be the scientist, using floating and drifting buoys out in the ocean to determine the flow of ocean and in the end compare it to a very simplified, generalized diagram of the surface flow in the ocean.

By analyzing the drifting buoys, you will see how scientists determine the flow of the surface circulation, second you will see how the data are analyzed, going from the raw drifter motion each month to an average or mean velocity of the drifters per year, for example, one year, to get a generalized view of circulation and then to a very simple diagram for the layperson that does not exhibit some of the fascinating complications that we see in the data.

We will end with an examination of the boundary currents, along the edges of the ocean, on either the western side of the ocean, called western boundary currents, or the eastern side, called eastern boundary currents, for example the California current as an eastern boundary currents, which brings cold water south from the subpolar regions, so eastern boundary currents tend to be slow and carry cold water.

Western boundary currents, which are on the western side of the ocean basin, like the Gulf Stream off the U.S., and the Kuroshio, off Japan, move away from the equator, carrying warm water and they are also intensified due to the rotation of the earth and are fast.-moving.

The speed of the current is realted to the rotation of the earth, something called vorticity, and the piling up of water on the western side of the basin, which then has to flow back eastward.

Let's now look at the flow of the surface waters of the ocean.

Objective: Students will use a scientific approach to study a problem of the Earth and environment, specifically the global flow of surface waters in the ocean basin.

Let's first review where we left off last time with the ending page from the previous expedition -- your worksheet begins on the next web page.

 

Remember the previous map of the global wind patterns?

The directions of the winds form big circular loops with the major circular loop in the northern hemisphere rotating in a clockwise direction and in the southern hemisphere, in a counterclockwise direction.

We can trace the direction of surface currents below these winds in many ways, for example with current meters attached to the seafloor or with floats that are carried with the currents, just like the Nike tennis shows and rubber that you learned about in the previous expedition

• Here are "high tech" methods to determine the current direction.

• Listen to the brief Ocean Report again: Transcript:

  These drifters phone home -- they are drifting buoys used for ocean research. These drifters go with the flow and send messages home via satellite.

  I'm Peter Benchley and this is the Ocean Report.

  The U.S. National Oceanic and Atmospheric Administration, or NOAA, uses drifting buoys, called drifters, to study ocean currents. Drifters have parachuted out of airplanes into the ocean around Antarctica and have been placed in the path of hurricanes.

  A little closer to home, are a set of moored buoys. NOAA uses them to predict weather patterns by tracking ocean conditions. These buoys are found all along the coast of the United States and in the Great Lakes. They measure things like ocean temperature, wind speed and wave height.

  A NOAA website has picture of the buoys, which we will see in a later expediton, and let's you see the wind and wave measurements taken by the buoys, and students in some schools are adopting a buoy to watch the weather and ocean conditions. The website is also great place for answers to ocean questions, like what happens during a hurricane.

  If you want to hang around with some drifters go to www.ndbc.noaa.gov (not now as we will go there in a subsequent expeditions).

  The Ocean Report is a project of the Pew Charitable Trust

   

Drifter Buoys and Current Meter Moorings

Graphics from Gulf of Maine Aquarium

Using sea surface temperature as a means of tracing the flow of water, try to guess the location and direction of the major circular ocean currents, called gyres. You will find one in each hemisphere (northern and southern) of the major ocean basins.

Like sea surface temperature, as show below, atmospheric radioactive fallout, in the form of tritium, from nuclear tests is also used as a tracer for tracking ocean currents as discussed in the Ocean report clip from previosu expedtyion, but listen to it again if you wish:

Transcript:

As America tested nuclear weapons decades ago, radioactive compounds have been released into the atmosphere. There have been some unexpectedly positive results from this fallout though. The fallout has let scientists track ocean circulation.

I'm Peter Benchley and this is the Ocean Report.

To check for leaks in your pipes. a plumber drops in some dye and watches to see where the dye leaks out.

Scientists are using this approach on a grand scale to track how water moves in the ocean, but instead of dye, they are using so-called tracer compounds, One tracer is a byproduct of nuclear explosions, it is called tritium.

Nuclear testing in the 1960's sent a small amount of this compound high above the earth, then the tritium fell slowly into the ocean and it has been on the move ever since, carried by ocean currents.

In the 1970's some scientists saw a way to get a windfall on information from the fallout. They have been mapping the tritum as it spreads to learn the direction and speed of deep ocean currents.

Why so much interest in mapping deep currents? The vast, deep ocean currents, which circulate throughout the oceans, control the planet's climate. If ocean circulation patterns currents change, so does the planet's climate, so tracking tracers compounds is one way to get the long range weather forecast.

The Ocean Report is a product of the Pew Trust.

Today's Image of Global Sea Surface Temperature Provided by SSEC, University of  Wisconsin-Madison

On the next several pages, you will join a voyage on the R/V Ronald Brown to deploy drifter buoys and view maps from the Drifting Buoy Data Assembly Center (DAC) (do not go to site yet) of the National Oceanic and Atmospheric Administration.

"The primary goal of the DAC is to assemble and provide uniform quality control of sea surface temperature (SST) and surface velocity measurements. These measurements are obtained as part of an international program designed to make these data available in an effort to improve climate prediction. Climate prediction models require accurate estimates of SST to initialize their ocean component. Drifting buoys provide essential ground truth SST data for this purpose. The models also require validation by comparison with independent data sets. Surface velocity measurements are used for this validation." - from the Drifting Buoy Data Assembly Center (DAC)

These calculations are generated each month by tracking the locations of drifter buoys around the world, which are used to track the ocean currents each month with satellites.

This Month's Image of more than 875 drifter buoy locations
provided by NOAA's GDP Drifter Data Assembly Center (DAC)

Last Updated on
October 31, 2006

How can we trace the direction of ocean currents?

a) With current meters
b) With floats
c) by tracing water masses using sea surface temperature
d) All of the above
e) Only a and b