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Ocean Surface Topography from Space
EDUCATION
TOPEX/Poseidon On-line Tutorial - Part III

Part I.   |   Part II.   |   Part III.

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Dynamic Ocean Topography: Sept '92 & May '96

  • Maps of dynamic ocean topography are used to track ocean circulation.
  • Monthly images of this sea surface topography are available for 1992, 1993, 1994, 1995, and 1996.
  • What is the difference between the highest and lowest parts of the world's dynamic ocean topography? Answer
  • How does this compare to how much sea height is influenced by gravity? Answer

 
  • At top is the first monthly data set taken after the launch of the T/P satellite. At bottom is more recent data.
  • Do these maps look significantly different from each other? Why or why not? Answer
  • Notice where very low areas of sea level occur (shown as magenta and purple). How do these areas correspond to how heat is transported by the "Global Conveyer Belt"? Answer
  • As you know, maps of dynamic ocean topography are used to calculate the direction of surface currents. Can you draw the direction the ocean currents are moving?



Currents Calculated from Ocean Topography

Currents Calculated from Ocean Topography

  • The arrows on this map show the direction of surface geostrophic current calculated from T/P data.
  • In the Northern Hemisphere "hills" correspond to clockwise ocean currents and "valleys" indicate counterclockwise currents. The sense of motion in the Southern Hemisphere is the opposite.

 
  • Before satellites, it took many years of ship data to create a map of global ocean currents. Now, an updated map of ocean circulation is available every 10 days.



Changes in Sea Height Over Time

Changes in Sea Height Over Time

  • Sea surface variability maps are used to study the changes in the ocean over months or seasons. They show how currents vary over short times and distances due to eddies and seasonal changes in the temperature of the upper ocean layer.
  • Monthly images of sea surface variability are available for 1992,1993,1994,1995,and 1996.

 
  • In these examples, what is the overall difference in sea height across the globe? (Click on image to see the color scale) Answer
  • How does this compares to the overall difference in sea height associated with the dynamic ocean topography? Answer
  • The two maps are from different months during 1995. Can you guess which season each map represents? Answer
  • First, look at the top halves of both maps simultaneously and then, look at the bottom halves of both maps simultaneously. How do the "ocean seasons" look different in the Northern and Southern hemisphere? Why do they look different? Answer



Mapping Variability in the Pacific Ocean

Mapping Variability in the Pacific Ocean

  • These maps have the same data as the previous image but are plotted with the Pacific Ocean at the center.
  • Make profiles of sea surface height along the Equator from Borneo to Peru for each map. Click here to find out how.
  • How do these profiles compare? In what way are the graphs different from one another? Answer

 
  • In the Eastern Pacific, the difference in sea surface height between these maps is about 18 centimeters (7 inches).
  • How does this affect our climate?



Normal Pacific Ocean Conditions

Normal Pacific Ocean Conditions

  • This image represents normal conditions in the Equatorial Pacific Ocean in the Western Pacific (around New Guinea). Normally, "Trade Winds" blow steady from east-to-west and "pile up" warm ocean water at in the Western Pacific. The colors in the image correspond to sea surface height.

 
  • Click this image to see a 3-dimensional graphic showing the area around the Pacific Ocean. It diagrams how the Trade Winds interact with sea surface height, ocean layers, and heavy concentrations of rain.
  • Under "normal" circumstances, the Trade Winds blow west along the Equator and allow nutrient-rich, colder bottom water to come up, or upwell, along the coast of South America. This provides good conditions for fish production.
  • During these times, heavy rains are tied to the warm water concentrated in the Western Pacific Ocean, near New Guinea and Australia.



El Niño Conditions in the Pacific Ocean

El Niño Conditions in the Pacific Ocean

  • Most people have heard of "El Niño" but few realize that it is caused by the interaction between the Trade Winds and the ocean. A "minor" difference in sea surface height means a big difference in the where ocean heat is stored and where heavy rains and severe drought occur.

 
  • Click on this image to see a 3-dimensional representation of El Niño conditions around the Pacific Ocean.
  • The name El Niño was coined by those who fish the waters off of the west coast of Peru to refer to the warm currents that typically appear around Christmastime causing a decline in the fish population. In some years, however, this phenomenon is so severe that fishing is interrupted for many months.
  • For decades, climatologists have assembled data from around the globe in order to detect links to severe El Niño conditions. Pieces of the El Niño puzzle include dramatic shifts in normal conditions such as: drought in Australia, New Guinea, India, and Africa; mild winters in Canada; severe winters in California, Christmas Island (central Pacific), and Peru. Other, more subtle, evidence tied to severe El Niño conditions includes high pressure records in Australia, fishery production, patterns of marine life, changes in coral reefs, and few-degree increases in sea-surface temperature in the Pacific Ocean.
  • Scientists have concluded that all of these conditions are tied to weakened Trade Winds that allow warm ocean surface water to travel eastward. This warm water brings heavy rains that disrupt normal atmospheric conditions.
  • All of this is signaled by a rise in sea surface height of 18 cm (7 inches)!
  • A good way to monitor this relatively small change in the sea level that has a huge impact is the T/P satellite.
  • Can you guess the financial impact that the 1982 - 83 El Niño had (in U.S. dollars)? Answer



Improving El Niño Predictions

Improving El Niño Predictions

  • These images show recent attempts to model one El Niño event. At top is a computer simulation and at bottom is actual sea surface height data from the 1994 - 95 El Niño event. Notice how the computer model underestimates the true ocean signature.
  • Satellite altimetry data that spans over a decade will be obtained by T/P and its follow-on mission, Jason-1. These data will provide the key to unravelling how El Niño events form, what their long-term impact on the climate might be, and possibly predict future El Niño events.


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