Discussion on El Nino and la Nina

3.  El Niño is an abnormal and lengthy warming in the
eastern part of the Pacific Ocean. This natural
phenomenon occurs at irregular intervals of two to
seven years and last for nine months or two years at
most.
 Usually, it starts at the end of the year or during
Christmas season that is why; it is termed as El Niño
which means”Christ child”.

4.  Normally, as trade wind moves from east to west, it
collects warm air. But when trade wind is weakened, it
causes the piling up of warm surface water and making
the part of the Pacific Ocean warmer leading to El Niño
phenomenon. This happens when the upwelling of
colder water is blocked by the large quantities of warm
surface water. (The cause of the weakening of the
trade winds is still unknown and it is still being
investigated)

5.  Since the Pacific Ocean is to the east of the Philippines, El
Niño phenomenon will affect the country. When there is an
increase of the temperature in the eastern part of the Pacific
Ocean, it is expected that some areas in the Philippines will
experience this climatic phenomenon. Some areas in the
country will experience near to above rainfall and some areas
may experience drier than normal rainfall.
 El Niño will most likely bring severe drought. It is believed
that it causes stronger thunderstorm disturbance and massive
storms. It also causes the decrease the population of some
species.

7.  La Niña is the opposite climatic disturbance to El
Niño. This natural phenomenon may, but does not
always follow El Niño events. It may last for nine to
twelve months but in some cases, it lasts for two
years. This event is triggered by the cooling of the
eastern part of the Pacific Ocean. That‘s why, it is
sometimes called cold Pacific.

8.  Trade winds that move from east to west are strengthened.
Upwelling of colder water intensifies. Moving air brings along
too much water vapor. When it reaches the land mass such as
Philippines, precipitation is experienced. There would be an
increase of rainfall in some areas in the Philippines. For
instance, areas that experienced severe drought which caused
by El Niño may encounter above normal rainfall. But in some
cases, areas that experience dry season will be drier than
normal conditions. La Niña’s effects are the opposite of El
Niño.

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 Walker Circulation Cell – normal conditions
◦ Air pressure across equatorial Pacific is higher in
eastern Pacific
◦ Strong southeast trade winds
◦ Pacific warm pool on western side of ocean
◦ Thermocline deeper on western side
◦ Upwelling off the coast of Peru

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Walker Cell Circulation disrupted
 High pressure in eastern Pacific weakens
 Weaker trade winds
 Warm pool migrates eastward
 Thermocline deeper in eastern Pacific
 Downwelling
 Lower biological productivity
◦ Peruvian fishing suffers

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 Increased pressure difference across equatorial
Pacific
 Stronger trade winds
 Stronger upwelling in eastern Pacific
 Shallower thermocline
 Cooler than normal seawater
 Higher biological productivity

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 El Niño warm phase about every
2–10 years
 Highly irregular
 Phases usually last 12–18 months
 10,000-year sediment record of events
 ENSO may be part of Pacific Decadal Oscillation (PDO)
◦ Long-term natural climate cycle
◦ Lasts 20–30 years

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 1982 – 1983
 1997 – 1998
 Flooding,
drought,
erosion, fires,
tropical storms,
harmful effects
on marine life
 Unpredictable

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 Tropical Ocean−Global Atmosphere (TOGA)
program
◦ 1985
◦ Monitors equatorial South Pacific
◦ System of buoys
 Tropical Atmosphere and Ocean (TOA) project
◦ Continues monitoring
 ENSO still not fully understood