Ocean Currents of the World

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Kon Tiki
Ocean Currents of the World
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1947 Thor Heyerdahl Built a balsa wood raft in
the same design as ancient South Americans - the
Kon Tiki Set sail from Callao in Peru using
the prevailing winds and ocean
currents Travelled about 7000 km in just under 3
months Landed on the island of Raroia in
Polynesia Proved that ancient civilisations
could have migrated across the Pacific Ocean in
that way
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El Nino and La Ninya El Nino term used for
over 100 years around Ecuador and Peru to
describe development of warm ocean water along
the west coast of South America around
Christmas Decimation of annual anchovie
harvest, and death of seabirds who depend on
them Dead fish and birds along the coastline
in the area
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Release of hydrogen sulphide gas in to ocean
waters This gas blackens the paintwork along the
hulls of the local fishing boats out of the port
of Callao in Peru Known locally as the Callao
painter
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Today El Nino refers to the much broader scale
phenomenon of unusually warm water forming
across much of the tropical eastern and
central Pacific. These El Nino events do not
occur in any precise cycle but broadly speaking
tend to recur every 3 to 7 years and last around
12 to 18 months.
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The Walker Circulation - normal and El Nino
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Each El Nino event is different in terms of its
strength and impact on altered rainfall patterns
Life cycle of each event also varies in
timing and spatial extent
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The usual effects of an El Nino situation
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La Nina can be thought of as the reverse of El
Nino - Cooler than normal ocean temperatures
across much of the equatorial and central
Pacific - A La Nina event often, but not
always, follows an El Nino and vice versa
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NOAA Image
Thermocline Layer of water between the warmer
surface zone and the colder deep zone. In the
thermocline, temperature decreases rapidly with
depth.
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NOAA Image
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NOAA Image
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During an El Nino, sea level atmospheric pressure
(SLAP) tends to be lower over the eastern
Pacific and higher in the west. During a La
Nina, the opposite pressure distribution is
usual. This see saw in SLAP across the east
and West Pacific ocean is called the Southern
Oscillation or SO. Measured by constructing the
averaged difference in SLAP between Darwin and
Tahiti to produce the Southern Oscillation Index,
or SOI.
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Sustained negative values of the SOI are often
indicative of El Nino episodes Sustained
positive values - La Nina Since El Nino and the
SO are closely connected, the two terms are often
combined into a single acronym - ENSO - meaning
El Nino- Southern Oscillation
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Clues to look for in the development of an El
Nino
Increasing SSTs across central and eastern
Pacific
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Clues to look for in the development of an El Nino
Negative SOI
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Clues to look for in the development of an El Nino
Weakening of SE trade winds - westerly tendency
emerging
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Clues to look for in the development of an El Nino
Extra cloud over the central equatorial Pacific
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Effects of El Nino- La Nina on Fiji and Vanuatu
In general, drier and hotter weather than normal
is expected from December to February during an
El Nino event, followed by drier and cooler
weather from June to August - mostly due to NE
movement of SPCZ Above average rain can be
expected during a La Nina - SW movement of the
SPCZ There is often a considerable delay between
the SOI phases and the onset of anomalous
rainfall patterns across the area. This is very
useful because it allows a lead time (4 to 6
months) before the onset of a drought.
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Effects of El Nino- La Nina on Samoa, Tuvalu and
Tonga
Samoa Increased likelihood of drought during El
Nino Tuvalu Increased likelihood of drought
during La Nina Higher chance of cyclones
during El Nino Tonga Increased likelihood of
drought during La Nina (4 to 6 month lag
period) Higher chance of cyclones during El
Nino
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Paths of Tropical Cyclones
El Nino years
La Nina years