TOPEX/Poseidon altimeter data
reveal our Ocean Planet
V
iewed from space, the oceans give Earth its "blue
marble" appearance, setting our planet apart from all
others in the solar system. This cloak of life-giving
water that covers more than 70 percent of Earth's surface
area controls our planet's climate.
Studying the oceans, scientists are using TOPEX/Poseidon
satellite altimeter data to learn how heat from the Sun is
transported around the globe by ocean circulation patterns.
Altimeter data over the oceans are used primarily to determine
the sea-surface-height. From this data researchers have an
improved understanding of the role of the oceans in the
phenomenon known as El Niño, their role in controlling
seasonal variations and longer-term climate changes. TOPEX/
Poseidon data are also used for operational purposes, such
as monitoring eddies and their impact on human activities
and marine life.
The radar altimeter sends out short pulses of microwave
energy; the round-trip time of the pulses is used to calculate
the sea- surface topography. Corrections are made for a
variety of factors including the precise satellite orbit,
gravitational topography, atmospheric effects and ionospheric
effects and tides. Scientists and engineers have worked to
improve the corrections with the result that sea-surface height
measurements are now accurate to 2.3 cm.
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Backside Panel 1 from the poster
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“Rise and Fall of the ’97-’98 El Nino As Tracked
By
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TOPEX/Poseidon”
Jointly sponsored by the National Aeronautics and Space
Administration (NASA) and the French space agency Centre
National d'Etudes Spatiales (CNES), TOPEX/Poseidon has
continuously surveyed the oceans' surface with radar
altimeters since launch in 1992. The satellite orbits Earth
4,700 times per year, and engineers are optimistic that the
mission will continue to collect data through the year 2000.
The Jet Propulsion Laboratory (JPL) of the California Institute
of Technology manages the TOPEX/Poseidon mission for
NASA.
TOPEX/Poseidon
Earth’s Oceans Topography Experiment
Objectives
Solar Array
• Six-year global view of Earth’s oceans
Global Positioning
System Antenna
• Improved understanding of ocean currents
High-Gain Antenna
(1.2 m dia.)
• Improved forecasting of global environment
3.3 m
Satellite Bus
Highlights
Attitude Control
Module
• U.S.–France (Centre National d’ Études
Spatiales — CNES) program
Propulsion
Module
9
8.
m
• Launched August 10, 1992, on Ariane 42P
launch vehicle
• Sensors:
Power
Module
– Altimeters (NASA, CNES)
– Microwave radiometer (NASA)
Microwave Radiometer
5.5
Instrument Module
m
– Global Positioning System (GPS)
receiver (NASA)
Doppler
Tracking Antenna
(DORIS)
Laser Retroreflector
Assembly
– Laser retroreflector (NASA)
Wet mass: 2370 kg
Altimeter
Antenna
Dry mass: 2160 kg
– Doppler tracking receiver (CNES)
• Orbits Earth at 1336-km altitude, 66degree inclination
1992
1993
1994
1995
1996
1997
1998
2000
• 10-day repeat of ground tracks (± 1-km
TOPEX/POSEIDON
Measurement
System
accuracy)
Launch
8/10/92
GPS
Satellite
Satellite Orbit
Engineering Assessment
Completed 9/24/92
• Covers 95% of the ice-free oceans every
10 days
• Unprecedented accuracy: sea-level
measurements to within 5 cm
Radar Altimeter Signal
Verification Phase
Completed 2/22/93
• Has measured sea levels, mapped basin-
DORIS
Beacon
Prime Mission
3 Years
Extended Mission
Through 2000
Laser Ranging
Station
.
Gravity’s
Influence
on Sea Level
Ocean Topography
. ........... ....
........ ....
....................
wide current variations, monitored effects
of currents on global climate change;
studied El Niño phenomenon
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Backside Panel 2 from the poster “Rise and Fall of the
~
’97-’98 El Nino As Tracked By TOPEX/Poseidon”
El Niño
An El Niño is a disruption in the normal ocean circulation that
affects the weather worldwide. Relatively small changes in
ocean temperature over large area can make very big changes
in the weather patterns. An El Niño is a natural event which
occurs every 5-10 years. The term “El Niño” is used by those
who fish the waters off the coasts of Ecuador and Peru to refer
to the warm current that appears around Christmastime,
causing a decline in the fish population.
How does it work?
In a normal year, the easterly (westward-blowing) trade winds
push warm surface water against the western boundary of
the Pacific Ocean near Australia and Indonesia, while nutrientrich cold water wells up along the west coast of South America,
helping fish thrive. TOPEX/
Poseidon has tracked this
LOW RAINFALL
buildup of warm water in the
western Pacific Ocean, which
can be as much as 1 meter
higher than the eastern
Pacific.
An El Niño occurs when the
trade winds over the
equator weaken and even
reverse direction, that is,
they blow from west-toIndonesia
east. This allows the warm
"pile" of water normally held
against the western shore
of the Pacific to move
eastward along the equator.
When this bulge of warm water reaches South America it moves
north and south along the coast for hundreds of miles. When
the warm water bulge is against the shore of South America,
the normal upwelling of cool nutrient-rich water is prevented.
As a result, there is little for fish to eat and, in turn, few fish
for people to eat. The ocean also affects the atmosphere.
With the warm ocean, there is an increase in evaporation and
subsequent precipitation over the mountains in that area.
The effects of the El Niño reach considerably further than the
area surrounding the tropical Pacific; jet streams are altered
all over the world and many places have weather that is very
different from normal.
The change in the trade winds which leads to El Niño has yet
to be fully understood. The trade winds are controlled by the
interaction between the atmosphere and the ocean, with seasurface temperature an especially important factor. Scientists
are working to understand how and why the trade winds
change so that we can better predict El Niño's.
HIGH RAINFALL
weak trade winds
warm water
South America
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~
Backside panel 3 from the poster “Rise and Fall of the ’97-’98 El Nino As Tracked By
TOPEX/Poseidon”
Activity 1. Color the El Niño
33
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-10
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3 = LT BLUE
0
cm
Backside panel 4 from the poster “Rise and Fall of the ’97-’98 El Nino As Tracked By
TOPEX/Poseidon”
5
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4 = GREEN
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~
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2 = BLUE
270
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1 = PURPLE
225
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90
MAY 97
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MAR 97
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NOV 97
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225
270
6 = ORANGE
7 = RED
10
20
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SPACE GRANT CONSORTIUM
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Activity 1. Color the El Niño (continued)
30
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-30
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JAN 98
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1 = PURPLE
2 = BLUE
-20
-10
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3 = LT BLUE
4 = GREEN
0
cm
~
Backside panel 5 from the poster “Rise and Fall of the ’97-’98 El Nino As Tracked By
TOPEX/Poseidon”
4
6
3
2
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2
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5 = YELLOW
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MAY 98
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135
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270
225
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FEB 98
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225
270
6 = ORANGE
7 = RED
10
20
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SPACE GRANT CONSORTIUM
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El Niño Impacts
The 1997-1998 El Niño altered weather patterns all over the globe. Because
people and animals pattern their lives on average weather, most of the
impacts were negative. Some of the major impacts are listed below:
• Severe drought lowered crop yields in regions of Africa, Southeast Asia, Australia, and South
America. Over 60% of Algeria's wheat crop was lost, drought sent food prices soaring in Uganda,
70% of North Korea's maize crop failed with more than 60 rain-free days with temperatures near
90 deg. F. (32 deg. C)
• Flooding caused loss of life and road and property damage in central and southern South America.
Some locations in central Chile received the amount of their total yearly rainfall in a single day.
The increase in rainfall was due to increased moisture picked up over the eastern Pacific Ocean
that changed the path of the jet streams.
• Atlantic tropical storms and hurricanes were dramatically reduced in 1997. This decrease was
partly caused by abnormally strong high-level winds that blew from the eastern Pacific across the
tropical Atlantic to the Sahel region of Africa.
• The strength of hurricanes was increased in the eastern Pacific. Hurricane Nora was the strongest
hurricane on record for the eastern Pacific. Hurricane Pauline was also very strong and it hit
Mexico's Pacific resort coast with winds of up to 120 miles per hour. These hurricanes were fed by
high ocean temperatures.
• Ice storms in eastern Canada and New England caused some areas to be without power for over
a month as rain froze on contact with objects such as power pylons, telephone poles, wires and
trees. The weight of ice caused pylons to crumple and wires break. The Canadian army was
deployed to help in cities and on farms.
• Sea lions and other marine mammals starved off the California coast because warm water blocked
the normal upwelling of cold nutrient-rich coastal water. Some of the more fortunate were rescued
and nursed back to health. The lack of nutrients in the ocean resulted in less abundant plankton,
organisms which are the foundation of this marine food chain.
• Forest fires in Indonesia, started by people clearing land in an area suffering from prolonged
drought , blazed out of control because vegetation was so dry. Smoke polluted air over thousands
of miles caused health problems and is blamed for the crash of a jetliner that killed over a hundred
people.
• Relatively warm temperatures across much of southern Canada and northern USA was good news
to golfers but poor news for skiers. Demand for heating fuels decreased dramatically and there
were lower fuel prices elsewhere in the USA.
~
Backside panel 6 from the poster “Rise and Fall of the ’97-’98 El Nino As Tracked By
TOPEX/Poseidon”
TE
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SPACE GRANT CONSORTIUM
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Activity 2. Track the El Niño
Color the TOPEX/Poseidon images that show the rise and fall of the 1997 - 1998 El Niño so that areas of similar
height are the same from one month to the next. These maps show the sea-surface height anomaly which is the
difference between the height during that particular 10-day period and the average height for that time of year.
High areas correspond to warm water, low areas correspond to cold water . Use a color scheme that gives you a
map that is easy to interpret .
25 APR 97
Learn More About the El Niño
There is a lot that you can discover about the El Niño by looking
at your map.
(1) Which way did the warm water travel?
(2) The El Niño was at a maximum in November. How can we
know that?
10 NOV 97
(3) How long did it take for the El Niño to reach a maximum?
(4) How long did it take for the El Niño to disappear?
(5) Look at a map of the United States, how far north were
coastal waters affected by the El Niño?
(6) How big was the area of warm water compared to your
state or country?
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~
Backside panel 7 from the poster “Rise and Fall of the ’97-’98 El Nino As
Tracked By TOPEX/Poseidon”
14 MAR 98
Activity 3. Hills and Valleys of the Sea Surface
The surface of the sea is not flat; It consists of “hills and valleys” – high and low levels of water that make up its “ocean
topography”. (Select one of the maps of Activity 1, and ask your friends to choose other maps from the same series.)
Build an Ocean Topography Model
(1)
Collect the materials you will need: colored ocean
topography maps from plate 4 or 5, tracing paper, pencil,
thin cardboard, card stock, scissors, glue, paint (optional).
(2) Enlarge the map on a photocopy machine if you want
to have a bigger model.
(3) Place the tracing paper on top of the map you have
selected. Trace the contours of the surface by outlining each
of the different colors on the image (You will be following
the contour lines or the print). Use the scale to determine
the height of each area.
(4) Trace the line of each contour onto a separate sheet of
card stock, then cut out each contour outline. (Optional:
Use different color card stock for each contour level. You
may buy colored stock, or paint what you have.)
(5) Cut small pieces of cardboard to place between each
layer. (The cardboard provide a means of indicating the
relative height of each contour.)
Discover More About Oceans and El Niño; Look
Carefully at Your Models When Answering These
Questions:
(1) What is the difference between the highest and the
lowest points of the ocean surface, and how did this
difference vary with time?
(2) How does the sea-surface topography compare to land
topography? Are they very similar or very different? Why?
(3) How might the ocean topography affect ocean currents
? Hint: think about which way the water will flow, and look
at meteorological maps.
(4) What other measurements from satellites , ships, or
buoys might help scientists to understand El Niño conditions?
The above material is adapted from the CD-ROM
“Visit to an Ocean Planet.” See the CD-ROM for
more in-depth activities:
http://topex-www.jpl.nasa.gov/education/cdrom.html
(6) Position cardstock and cardboard on the tracing paper,
glue the cardstock cutouts one on top of each other to build
the model of the sea surface.
(7) Display the series of models to show the rise and fall
of the 1997-1998 El Niño.
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Backside panel 8 from the poster “Rise and Fall of the ’97-’98
~
El Nino As Tracked By TOPEX/Poseidon”
LEARN
MORE!!
Visit our TOPEX/Poseidon website at
http://topex-www.jpl.nasa.gov
(Science and education pages with links to related sites.)
On the Web
• El Niño
– JPL; http://topex-www.jpl.nasa.gov (Science and
education pages with links to related sites.)
– NOAA El Niño; http://www.pmel.noaa.gov/toga-tao/elnino/home.html (El Niño and La Niño pages with data
from satellites and buoys.)
– NOAA Forecasts; http://nic.fb4.noaa.gov/ (Maps on
anomalies and tutorials.)
CD-ROMs:
Two CD-ROMs are available through http://topexwww.jpl.nasa.gov/education/education.html
“Perspectives on an Ocean Planet” (Informational)
“Visit to an Ocean Planet” (Educational )
Slide Set
• TOPEX/Poseidon Education Outreach
– http://www.tsgc.utexas.edu/tsgc/topex/ (Great pages
with activities and information from the Center for Space
Research and the Texas Space Grant Consortium.)
– http://www-ocean.tamu.edu/education/oceanworld/
(Lesson plans and featured oceanographic topics from
Texas A&M.)
• Resources for Oceanography and Earth Science
Educators
– http://podaac.jpl.nasa.gov/edudoc.html (A 50 page
,on-line document, also available in hardcopy.)
• Bulletin boards and “Ask a scientist”
– http://www-ccar.colorado.edu/wwwboard/outreach/
(Outreach Bulletin Board);
– http://www.tsgc.utexas.edu/tsgc/topex/tpask.html
(Ask a Scientist.);
– http://www-ocean.tamu.edu/education/oceanworld/
Ask_Dr._Bob.html (Ask Dr. Bob.)
The El Niño slide set is available from the Finley-Holiday
Film Corporation. Telephone: 1-800-345-6707.
Hard Copy Materials
Posters, brochures, lithographs and other hard copy
materials are available upon request from
[email protected], or from
TOPEX/Poseidon Project Outreach Office
Mail Stop 264-686
4800 Oak Grove Drive
Pasadena, CA 91109.
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Backside panel 9 from the poster “Rise and Fall of the ’97-’98
~
El Nino As Tracked By TOPEX/Poseidon”