This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ESA News
http://www.esa.int

4 March 2003
 
ERS-2 data used in El Nino animation
====================================

A vivid animation based on data from ESA's ERS-2 satellite shows the 
onset of the recent El Nino phenomena from July to December of last 
year.

Covering a large area of the Pacific Ocean from South America to 
Australia and southeast Asia, the animation demonstrates the three 
most important factors that mark a phenomenon that can shape weather 
patterns from South America to Australia, and from India to southeast 
Asia:

* sea surface temperature
* sea surface levels
* winds

Surface water temperature is represented as deviations from average 
temperature values by the colour of the water surface. The 
greenish-blue colour represents the average temperature of the water. 
The purple colour represents a temperature 8 deg. Celsius above 
average, while the blue represents the other extreme of the scale, 8 
deg. Celsius below average.

The height of the ocean water, as a deviation from average levels, is 
seen by the shape of the sea surface, an effect that is difficult to 
see because of the compression of the video. The 'wave' effect of the 
surface represents the amplified deviation of the water's surface from 
its average height; the highest 'waves' display deviations from the 
average of about 1.8 metres. 

The wind is shown as blue arrows. Trade winds in the area, blowing 
constantly from east to west, are clearly visible, particularly in the 
final months of 2002. Winds blowing in this direction, pushing warm 
surface water to the west, is consistent with a weak, or weakening, El 
Nino.


El Nino expected to weaken
--------------------------
According to the US National Weather Service's Climate Prediction 
Center (CPC), El Nino conditions continued during January 2003, but 
there were indications that the warm episode is beginning to weaken.

"Consistent with current conditions and recent observed trends, most 
coupled model and statistical model forecasts indicate that El Nino 
conditions will continue to weaken through April 2003," the CPC 
forecast states. "Thereafter, the consensus forecast is for 
near-normal conditions during May-October 2003."

The animation incorporated data from several ERS-2 instruments. Sea 
level measurements were obtained by the radar altimeter, an active 
microwave sensor designed to measure return echoes from ocean and ice 
surfaces.  ERS-2's Along Track Scanning Radar (ATSR) acquired the data 
on temperatures of the sea surface temperatures.  The European Centre 
for Medium-Range Weather Forecasts, an international organisation for 
weather data, provided the wind data used in the animation.

What causes El Nino?
--------------------
In Spanish El Nino means 'the Christ Child' -- a name given to it by 
the Peruvian fishermen who hundreds of years ago noticed how sometimes 
their coastal waters grew unusually warm and fish grew scarce around 
Christmas time. They had no way of knowing they were naming a vast 
weather pattern whose effects strike much of the globe.

El Nino is an irregular oscillation in tropical Pacific currents, 
around the Equator. Usually, the wind blows in a westerly direction in 
this region. This pushes the warmer surface water into the western 
Pacific (which can be as much as a half-meter higher than surface
levels in the east). In the eastern Pacific, colder water from below 
the ocean's surface is pulled up from below to replace the water 
pushed west. So, the normal situation is warm water (about 30 C) in 
the west, cold (about 22 C) in the east.

In an El Nino, the winds pushing that water to the west get weaker. 
With thermal circulation some of the warm water piled up in the west 
is released and moves back east, and not as much cold water gets 
pulled up from below. This makes the water in the eastern Pacific
warmer, an El Nino trademark. 

El Nino doesn't stop there. Warmer ocean waters weaken the winds, 
which in turn further warms the water, a cycle that makes El Nino even 
stronger. This can have wide-ranging consequences on climate patterns 
around the world. These can include vastly increased rainfall in South 
America, drought in Australia and fires across southeast Asia, dying 
coral reefs in India, severe winter storms in California, a heat wave 
in Canada and intense hurricanes raging along the Pacific Ocean.

This phenomenon seems to occur every three to seven years.  The El 
Nino of 1997-98 is estimated to have caused more than Euro 30,000 
million of global property damage and an unknown toll in human lives.

Several versions available
--------------------------
Several high-resolution versions of the animation are available in 
Windows (.avi) and Quicktime (.mov) formats (please be patient while 
they load). To view the animation, click on the preferred version.

* 160x120 resolution:

  Windows (2.8MB)
  http://ravel.esrin.esa.it/video/nino7.avi

  QuickTime (3.6MB)
  http://ravel.esrin.esa.it/video/nino7.mov

* 320x240 resolution:

  Windows (9.6MB)
  http://ravel.esrin.esa.it/video/nino6.avi

  QuickTime (9.5MB)
  http://ravel.esrin.esa.it/video/nino6.mov

Related articles

* Satellite eyes focus on El Nino
  http://www.esa.int/export/esaCP/GGGN8H2UGEC_FeatureWeek_0.html
* El Nino is yawning
  http://www.esa.int/export/esaSA/ESANWPVTYWC_earth_0.html

Related links

* Protecting the environment
  http://www.esa.int/export/esaCP/Protecting.html
* El Nino
  http://earth.esa.int/eeo4.20104

 - End of File -
================

---