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El Niño conditions: Warm water pool approaches the South American coast. The absence of cold
upwelling increases warming
region on any regular basis because
the effects seem to shift around –
occasionally missing out some areas
all together and at other times
causing unseasonable temperature
fluctuations, floods or droughts in
those very same places. Because of
this, it is sometimes difficult to predict severity or where that severity
will bite the hardest. And unfortunately, by the time El Nino’s pattern
emerges, it may be too late for
farmers to do much about it. Although there are often several years
between each El Nino event –
sometimes followed by its little sister, La Nina – each episode can play
havoc with crop production.
So what causes El Niño and La
Niña?
What we do know about this occurrence is how it happens. What we
don’t fully understand, is why. The
Pacific is the largest body of water
on the Earth and covers nearly half
the planet. So when any anomalies
take place across this vast area, it is
naturally going to affect weather
patterns in many areas across the
globe. Any changes in the ocean
will impact the atmosphere and
therefore affect climate patterns. In
turn, changes in the atmosphere
impact the ocean temperatures and
currents. However, possibly the biggest single culprit may be the sun
which affects atmospheric pressure
around the globe.
El Niño
El Nino comes about through a
shift of influence between a low
pressure area in the west of the
equatorial Pacific and a high pressure area in the eastern Pacific. Under normal conditions air flows
from the high pressure area to the
low area, creating the strong westerly trade winds that draw the
warm surface water away to the
west, thus cooling the ocean along
the Pacific South American coast.
However, this pressure gradient
sometimes lessens as the pressure
areas undulate slightly. With a lesser gradient, the wind weakens and
no longer cools the ocean, thus
allowing the sea surface temperature (SST) in the eastern Pacific to
become warmer. This causes changes in the atmospheric conditions
which move around creating a kind
of domino weather effect across
various countries. When SST anomalies are greater than 5C degrees,
then we know El Nino is on its way.
La Niña
However, like two balancing balls
on a see-saw, the pressure areas