Unpredictable Christmas Child
"There's a good
chance 2002 will be an
El Nino, a sudden shift of warm sea surface water, changes the normal
above the Pacific. And that turns over the weather around the
The Ocean researchers are alert: "there's something going on; something
El Niño-like" .
El Niño is as old as the world. The Inca's in Peru already
knew of this phenomenon, and built their cities upon the hills, far
away from the unpredictable water with its sudden flooding. Geologists
found 13000 year-old traces of El Niños in Peruvian coastal villages. Written reports of
El Nino effects in Peru go back to
But this Spanish "Christmas Child", was named "El
Nino" by Peruvian fishermen; at the end of the 19th century. They
discovered that once in odd
years around Christmas time, the anchovy and sardine's suddenly
vanished without trace.
The fish had moved; thousands miles to the south, to the Chilean coast,
where the sea water was colder -- and more abundant
in food that the warmer waters..
At the Peruvian and Ecuadorian coast, usually an Eldorado for
fishermen, an enormous pool of warm
water suddenly appeared, about 25 º C some 5
degrees warmer than normal.
The nets were empty, millions of seabirds and other animals
the guano-gatherers; earning a living by collecting nitrate-rich dirt
of cormorants, seagulls and penguins; searched in vain for this
El Niño had taken control for a while.
El Niño and the Ocean's seesaw.
and cold ocean water don't mix easily: in fact that's the reason for
the existence of El Niño's. The dividing line between warm water layers
(about 25 º C)
and cold (15 º C
and lower) is a sharp one; called a thermocline. In the Western
Pacific; near Australia and Asia, this line lies far deeper that in the
near the Americas. The trade winds blows the warmer surface water to
it piles up there. On the other hand, at the Eastern Pacific
as the warm
water is blown away; colder water will replaces it.
The thermocline through the Pacific does not lie horizontal.
It's deeper in the west and shallower in the east. It behaves like a
seesaw: with the movements of
ocean water; caused by currents and wind, it swings to and fro. That
very slow, for the ocean is incredible tardy. Its a process that takes
Ocean and the atmosphere
So the atmosphere and
interact and influence each other. The trade
winds also cause a change in temperature difference between the west
east of the Pacific. Air rises more above warm water than
water. If the air rises and becomes colder as it enters higher
water vapour in the air condenses and it rains: that is why in the
rains much more over the warm west near Asia than over the cold east
and Ecuador. Also, the rising air in the west sucks in more air, and
partly responsible for the strength of the trade winds.
If, for one reason of
another, the trade winds
slacken, it will cause the east to be less cold and the temperature
between east and west will diminish. And if the difference in
lessens, the trade winds will lose strength. In this way there is a
circle of causes and effects that can reinforce each other: weaker
trade winds give a
smaller temperature difference, this gives weaker trade winds and so on.
Weaker trade winds means that less warm water is blown to the western
the thermocline will rise in the West. The warm water moves inchmeal to
east; the coast of America gets slowly but surely a thicker layer of
This warm layer pushes the cold water to the deep; the thermocline
And what's more: the thermocline dips often to
the other side; - sinking in the east and rising in the west: its a
consolidating process. The thicker warm water layer in the east causes
temperatures of the air above. This air has the tendency to rise -- and
more air to the Eastern Pacific -- the opposite direction of the normal
winds. Sometimes this is so strong that the trade winds will ease
reverse. -- and as that trade winds were responsible for moving the
to the western pacific -- the thermocline in the west will rise more
El Niño is born: thanks to the seesaw of the Ocean.
The end of El Niño
The working of this seesaw also causes El Niño's end -- or
even the opposite
situation La Nina.
deviations in the trade winds - caused by the
higher-than-normal surface temperatures - are most strong in the middle
Pacific Ocean, around the date line (longitude 180º ). The thermocline
be deeper at that place as it is in the Eastern Pacific.
And this brings an El Niño to its end. All this warm water in the east,
by the winds around the date line, must come from somewhere, and that
regions a little north and south of the equator.
The thermocline will rise in those off-equatorial regions. Its like a
when you push the water down at one place it'll rise
shallow parts in the thermocline can move back to the equator.
reflections of the shallow parts at the western coast are important for
process. On the contrary, the deep part in the east has a tendency to
poleward, leaving the region where it can influence El Niño
Next, the shallow regions in the west travel eastward along the
overcome the wind anomalies, and eventually the thermocline in the east
will rise again.
While the ocean tries to find it normal balance; the thermocline in the
rise above its normal level and a state develops which is known as La
with colder than normal surface waters in the east, and stronger than
trade winds. This mechanism, which consists of a quasi-instantaneous
feedback, followed by a delayed negative feedback, is known as the
and the weather around the globe
will agree: El Niño is a
quite innocent name for such a phenomenon bringing trouble and disaster
parts of the world. Floods and heavy rain in South America's west coast
extreme drought and famine in Australia, India, Asia and Africa. Even
European weather is likely to be influenced by El Niño.
But meteorologists think that El Niño's
reputation is very blackened by the media -- and therefore by the
The phenomenon is almost a synonym for tornado's, hurricanes,
downpours, floods, extreme droughts, abortive harvests and
forest-fires. After almost every natural disaster the media
blame it on El Niño -- even when it hasn't been an
El Niño year at all -- and when it isn't El Niño;
its the greenhouse-effect or global warming. Nonsense of course, El
is a natural phenomenon, it belongs to the earth and atmosphere. It
However during an El Niño Indonesia, the Philippines, Middle and South
America's west coast are in severe danger. Due to the last El Niño
Indonesia suffered a terrible famine and enormous forest-fires, which
set up the
whole area in a thick layer of smoke for months. Many floods and
Middle America brought disaster and drew the attention of the whole
El Niño also has positive
effects; especially in North America. There are less hurricanes on the
and tornado's in the US. The North East of America
is warmer than normal -- so less to burn -- for the polar jet stream
very far south during an El Niño.
California has more rain than normal, but it falls more equal - like
drizzle - so there's not so much damage to the road. The Californian
catch suddenly the most exotic tropical fish, in marvellous colours --
these fish do not come so far north.
and the research
El Niño brings so much trouble and
disaster throughout the world; it'll be a good thing that an El Niño
can be forecasted and eventually measures can be taken. And for
and meteorologists El Niño is a really
'It influences the worlds' weather in a striking organized order. But
we do not
understand the whole phenomenon properly. The ocean is slow, very dim.
sure moves. The so-called Kelvin- and Rossby-waves - which somehow play
in the El Niño development - move about 2
meters a second. You easily could walk with such a wave. The water
although very tardy - but it does - you can't stop an El
speed the ocean may move at human pace; the amounts of water which is
across the Pacific; set going by El Niño,
goes beyond every imagination. "Within five to ten years we'll know
Hopefully at that time we'll have climate-models that can predict
All eyes are
upon 70 TAO-buoys laid down in the Pacific Ocean. TAO stand for
Atmosphere Ocean. They are posted since the eighties along the equator
worlds first warning system for disruptions in the tropical ocean. They
daily measurements of water temperature - to 500 meter depth
pressure and humidity. These data are sent via a satellite-system to
Marine Environmental Laboratory in Seattle; and to other
throughout the US, Europe and Japan. "We have a good three-dimensional
of the ocean. The system is expensive and complicated a costs over a
million dollars a year for maintenance. But its worth it: we know much
about the El Niño-movements and every step
brings us closer" .
El Niño indices
How strong is
an El Niño? You can measure it in two ways: The
Niño-3 index and the Southern Oscillation Index.
The one most used for the El Niño force is
the Niño-3 index. It measures the water temperature in the Eastern
the area between - 5º
and + 5 º
latitude and - 150º
longitude). The Niño-3 index
swings between - 2
C and + 4º C; mostly between + 1º C and - 1º C. During a
heavy El Niño
the sea water temperature can have a variation of 5 - 8 º
Except the warmer-than-normal sea water, there also is a
difference in air pressure between Tahiti and Darwin (Australia) during
an El Niño.
This difference in pressure is called the Southern Oscillation Index,
between - 3 and + 3. The Southern Oscillation (southern swing; term
Gilbert Walker, an English meteorologist during the 1920's) is the
pressure above the Pacific and the variation in the trade winds that's
Niño and the
(ENSO) are the main authors of the climate changes across the globe.
Want to know
Niño-sites on the
are a few to help you on the way
Quotations from interviews with G.J. van Oldenborgh and G.
By Wijke Ruiter