Major Ocean Currents

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Introduction

The wind blowing over the oceans causes the surface water to move and provides the major force that produces the ocean currents. The oceans in turn help transport the excess heat of the tropics poleward, affect local coastal weather and climate, provide the energy for hurricanes and mid-latitude storms, and can affect weather world wide when there are large climatological deviations.

Objectives

Observe sea-surface temperature patterns associated with the major ocean currents, storm development, and the El Niņo

References

Global Wind Patterns and the Oceans in Chapter 7 of your text.

Instruction & Web Examples

Major Ocean Currents: The major surface ocean currents of the world transport warm water toward the poles and cold water toward the equator. To see this, refer to the map of Major Ocean Currents on page 188 in your text, and then inspect the sea-surface temperature (SST) links below. Each of the maps uses color-coded contours of SST, SST climatology (average SST for the period indicated), or SST Anomalies (differences between current SST and SST climatology). On each map be sure to notice the map type, date, and units. Notice the specific currents affecting the United States (Gulf Stream, Labrador Current, California Current), as well as the North Atlantic Drift and Humbolt Current.

Oceans, Weather, and Climate: The weather and the climate of coastal locations is profoundly affected by the particular combination of wind direction and water temperature. In the Controls of Temperature activity of the Unit 4 Lab, we used Climographs and World Climate Data to inspect the effect on average temperature of ocean currents and location relative to large bodies of water.

We can easily observe the effect of wind direction on day-to-day weather right here along the coast of Maine. Any time there is a significant difference between the Gulf of Maine SST and the inland temperature, an onshore wind will produce coastal temperatures that are warmer than the inland temperatures if the water is warmer and cooler than the inland temperatures if the water is cooler. To check this out, use the links below to obtain the water temperature and the winds at some coastal locations. Then, if the winds are onshore near the coast line, and compare the coastal and inland temperatures.

Gulf of Maine SST

Current Weather Reports for Maine

Storms: The warm waters of the Atlantic Ocean and the Gulf of Mexico can provide the energy for mid-latitude storm systems to develop and intensify in the winter season and for hurricanes to form in the summer and fall.

We'll discuss the development of mid-latitude storms in detail in the next unit. For now, just note that one of the favored areas for wintertime development and intensification of these storms is off the east coast over the Gulf Stream. The reason is that the very cold air flowing off the land over the very warm Gulf Stream water results in high evaporation rates and latent energy transfer to the atmosphere.

If it is a late fall through early spring month, check the Forecast Maps at NCAR to see if a storm is predicted to develop or intensify over the Gulf Stream.

We'll put off the detailed discussion of tropical storms and hurricanes until Unit 13. However, we will note now that for hurricanes to form, the surface water temperature must normally be 26.5°C (80°F) or warmer to a depth of about 200 meters over a large area. Check the World SST at one of the links given above. If the current month is a winter or spring month, it should be obvious from the SST's why hurricanes only rarely form in the Atlantic Ocean in those months. If the month is June through October, you will get some idea of how vast the portion of the Atlantic is in which hurricanes might form, if all other conditions are also right.

El Niņo and the Southern Oscillation: The extensive and prolonged ocean warming that occurs along the coast of Peru and Ecuador every 3 to 7 years and known as El Niņo, has been presented adequately in the text. For additional information, I encourage you to read the El Niņo Online Guide at the University of Illinois or do an online search for El Nino or ENSO.

Practice Questions

Use the mid-February images below to answer the following questions.

1. What is the range of SSTs' in the Gulf of Maine?

2. What are the coldest and warmest SST's in the upper image in both Celsius and Fahrenheit degrees?

3. What are the names of the major ocean currents associated with the coldest and warmest SST's?

4. Does a mid-latitude storm system appear to be developing or intensifying over the Gulf Stream?

Answers

1.   About 3-7°C
2.  0°C & 25°C, 32°F & 77°F
3.  Labrador & Gulf Stream, respectively.
4.  A mid-latitude storm is moving through the Gulf Stream region and is probably intensifying.

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