Locating+the+Gulf+Stream

The use of satellite imagery is one of the most accurate ways to locate the Gulf Stream. NOAA (National Oceanic and Atmospheric Administration) operates a Polar Orbiting Satellite (POES) with an AVHRR sensor (Advanced Very High Resolution Radiometer). This sensor measures the amount of thermal infrared radiation given off by the surface of the ocean. The amount of thermal infrared radiation given off by an object is related to its temperature, so by measuring the amount of radiation given off by the ocean, scientists can calculate the temperature of the sea surface. The satellite thermal infrared radiation data is color coded to produce an image of the ocean. The satellite image allows people to easy locate the warm current of water in the Atlantic Ocean known as the Gulf Stream by comparing the color differences to a color/temperature scale. Sea surface height (radar altimeter data), measured by the TOPEX/Poseidon and ERS-2 satellites also is valuable information to help track down the location of the Gulf Stream. The Radar Altimeter on ERS-2 sends radar signals to the earth and ocean surface and collects the return signal. That information is processed to reveal the ocean wave height and wind speed (over oceans), the surface backscatter, and the height of the satellite above the surface. This provides the possibility to monitor the global ocean circulation and regional current systems. The satellite system offers the advantage of daily global coverage. Other means of measuring sea surface temperature such as buoys (drifting and moored) are used to maintain accuracy of the satellite data, further removing sources of error.

Oceanographers use the images to visualize the Gulf Stream; the width, the number of rings and meanders, etc. Constant monitoring is necessary because the Gulf Stream is not a stable current, it meanders North and South. Sometimes these meanders are small, taking the form of waves which appear to break backwards relative to the northeasterly flow of the current. In some instances, the meanders become so large that a pocket of warm water is pinched off and separates from the stream into the cooler shelf water. These are called warm core rings. The warm core rings rotate clockwise for several days, eventually drifting west to southwest until they interact with the shelf or the Gulf Stream. Most warm core rings are reabsorbed into the stream after wandering for 1 to 3 months. The effects of warm core rings were observed by early oceanographers, but the true extent was not well understood until the availability of satellite imagery. It is also interesting to note that just as stream meanders to the North can pinch off a warm core ring, stream meanders to the South can also pinch off, forming a cold core ring. These rings are often less visible in the satellite imagery because of the warmer water lying above, but can still be seen by the trained eye. ([|Northern Gulf Stream Image June 11, 1997])

[|Full Basin] [|Western Atlantic] [|Blank Gulf Stream Map]

** Procedure ** Break into working groups of 4 students. Divide each group into 2 pairs.

__ Pair 1 __ 1. Obtain the most recent data from the following buoys. Record the following information on the Student Worksheet: Latitude and Longitude, Time and Date, Air Temperature (ATMP) and Water Temperature (WTMP). Scroll down the page to the Previous 24 observations. Plot the location of the 6 buoys on the chart.

(Station 44008)  ||   [|Georges Bank Buoy] (Station 44011)  ||   [|East of Cape May Buoy] (Station 44004)  || (Station 44009) ||  [|East of Cape Hatteras Buoy] (Station 41001) ||  [|South Hatteras Buoy] (Station 41002) ||
 *  [|Buoys] ||
 * [|Nantucket Buoy]
 *  [|Delaware Bay Buoy]

__Pair 2__ 2. Obtain the most recent ship data by clicking on the Ships in the North Atlantic link below. The symbols represent the ships and buoys currently logging data in the Northern Atlantic. The red symbols are buoys and the blue symbols represent ships. Notice the series of letters and numbers under the blue ship symbols. These are the "Ship IDs". No two sets of letters and numbers are the same. Locate at least four ships between 30N - 50N Latitude and 50W - 80W Longitude. Write down the exact "Ship ID" on the Student Worksheet.

[|Ships in the North Atlantic]

3. Now click on the Ships Observations Report link below. Look through the data reported by the ships selected from the North Atlantic map. Record the water temperature. Record the location of the ship(s).

[|Ships database]

**NOTE:** If the Ship ID does not show up in the current hour observations, use the drop down Time menu and get the data for the previous hours.

**Team Assessment** Refer to the satellite image of the Gulf Stream and to answer these questions.

[|Real Time Sea Surface Temperature Satellite Data]

Compare the ocean water temperature data from the satellite image with the temperatures collected from the ships and buoys.

1. How close do the data sources compare?

2. With the availability of satellite imagery, why do you think scientists continue to collect data from ships and buoys?

Analyze satellite imagery. Review the following archived satellite images and answer the questions on the Student Worksheet.

[|October 23, 2002] ||
 * [|January 29, 2002] ||  [|April 19, 2002]  ||
 * [|August 28, 2002] ||
 * Archived images from the Ocean Remote Sensing Group, Johns Hopkins University Applied Physics Laboratory ||

3. Does the position of the North Wall (the Northern boundary of the Gulf Stream) fluctuate greatly during the year? Explain.

4. Describe yearly sea surface temperature changes of the Northwest Atlantic Ocean.

5. Study the satellite image below. Based on the information in the image, estimate the time of year. Support your answer.