Download El Nino (warming) and La Nina (cooling) - DP

El Nino (warming) and La Nina
(cooling)
Videos available
• The Intertropical Convergence Zone (ITCZ) is
the area encircling the earth near the equator
where winds originating in the northern and
southern hemispheres come together.
• Solar radiation warms the air over the
equator, causing it to rise. The rising air then
proceeds south and north toward the poles.
From approximately 20° to 30° North and
South latitude, the air sinks. Then, the air
flows along the surface of the earth back
toward the equator.
• Sailors noticed the stillness of the rising (and not
blowing) air near the equator and gave the region the
depressing name "doldrums."
• The doldrums, usually located between 5° north and 5°
south of the equator, are also known as the
Intertropical Convergence Zone or ITCZ for short.
• The trade winds converge in the region of the ITCZ,
producing convectional storms that produce some of
the world's heaviest precipitation regions.
• The ITCZ appears as a band of clouds, usually
thunderstorms, that circle the globe near the equator.
• In the Northern Hemisphere, the trade winds move
in a southwesterly direction from the northeast,
while in the Southern Hemisphere, they move
northwesterly from the southeast.
• When the ITCZ is positioned north or south of the
equator, these directions change according to the
Coriolis effect imparted by the rotation of the earth.
• For instance, when the ITCZ is situated north of the
equator, the southeast trade wind changes to a
southwest wind as it crosses the equator.
• The ITCZ moves north and south of the equator
depending on the season and solar energy received.
The location of the ITCZ can vary as much as 40° to
45° of latitude north or south of the equator based
on the pattern of land and ocean.
Schematic representation of inertial circles of air masses in the
absence of other forces, calculated for a wind speed of
approximately 50 to 70 m/s.
Plus a map of global Oceanic currents.
The Jet Stream – used by air craft to
more faster around the globe.
• The trade winds are the prevailing pattern of
easterly surface winds found in the tropics,
within the lower portion of the Earth's
atmosphere, in the lower section of the
troposphere near the Earth's equator.
• The trade winds blow predominantly from the
northeast in the Northern Hemisphere and
from the southeast in the Southern
Hemisphere, strengthening during the winter.
• Historically, the trade winds have been used by
captains of sailing ships to cross the world's oceans
for centuries; and enabled European empire
expansion into the Americas, and trade routes to
become established across the Atlantic and Pacific
oceans.
• In meteorology, the trade winds act as the steering
flow for tropical storms that form over the Atlantic,
Pacific, and south Indian Oceans and make landfall in
North America, Southeast Asia, and India,
respectively.
2) Important cause- Trade winds move warm water
and air west towards the Caribbean.
Due to the Coriolis Force.
1) Heat
from the
sun warms
the Ocean
surface
Thermocline.
layer of water
with temperature
change:
a layer of water,
e.g. in a lake or
Ocean, where
there is an abrupt
change in
temperature that
separates the
warmer surface
water from the
colder deep water
3) The cooler water is from the Humbolt
(peruvian) current and is nutrient rich.
3) Cold water
is pulled
upwards,
replacing the
warm surface
water.
NORMAL CONDITIONS – Key features
• During non-El Niño conditions, the Walker circulation is
seen at the surface.
• Easterly trade winds move water and air warmed by the
sun towards the west.
• This also creates ocean upwelling off the coasts of Peru and
Ecuador and brings nutrient-rich cold water to the surface,
increasing fishing stocks.
• The western side of the equatorial Pacific is characterized
by warm, wet low pressure weather
• Collected moisture is dumped in the form of typhoons and
thunderstorms.
• The ocean is some 60 centimeters (24 in) higher in the
western Pacific as the result of this motion.
The Thermocline…
• “There exists in most ocean areas (apart from polar and
sub-polar oceans) a zone where the rate of decrease of
temperature is much larger compared with that above and
below, hence the definition.”
• Depending on the geographical location, the thermocline
depth ranges from about 50m to 1000m.
• A simplified view is to consider the thermocline as the
separation zone between the mixed-layer above, much
influenced by atmospheric fluxes, and the deep ocean.
• In the tropics, the thermocline can be quite shallow on
average, as in the eastern Pacific (50m), or deeper as in the
western part (160-200m).
E-N-S-O
• El Niño-Southern Oscillation, often called simply ENSO, is a climate
pattern
• Occurs across the tropical Pacific Ocean on average every five years
• but over a period which varies from three to seven years, and is
therefore, widely and significantly, known as "quasi-periodic." \
• ENSO is best-known for its association with floods, droughts and other
weather disturbances in many regions of the world, which vary with each
event.
• Developing countries dependent upon agriculture and fishing,
particularly those bordering the Pacific Ocean, are the most affected.
WHAT IS EL NINO?
• ENSO is composed of an oceanic component, called El Niño (or La
Niña, depending on its phase), which is characterized by warming or
cooling of surface waters in the tropical eastern Pacific Ocean, and…
• an atmospheric component, the Southern Oscillation, which is
characterized by changes in surface pressure in the tropical western
Pacific.
• The two components are coupled:
• when the warm oceanic phase (known as El Niño) is in effect,
surface pressures in the western Pacific are high.
• When the cold phase is in effect (La Niña), surface pressures in the
western Pacific are low (volatile weather).
ORIGINS
• In popular usage, El Niño-Southern Oscillation
is often called just "El Niño". El Niño is Spanish
for "the boy" and refers to the Christ child,
because periodic warming in the Pacific near
South America is usually noticed around
Christmas."La Niña" is Spanish for "the girl."
This reduces the efficiency
of upwelling to cool the
surface and cut off the
supply of nutrient rich
thermocline water to the
euphotic zone
KEY CAUSE - During El Niño
the trade winds relax in the
central and western Pacific
This leads to a
depression of the
thermocline in the
eastern Pacific, and
an elevation of the
thermocline in the
west.
Storms appear in
the central Pacific
and a carried by
the subtropical jet
stream towards
the W USA/
Central America/
Andean S America.
The latter of which
adversely affected higher
trophic levels of the food
chain, including
commercial fisheries in
this region
The result is a rise in
sea surface
temperature and a
drastic decline in
primary productivity
El Nino
• El Niño is defined by sustained differences in
Pacific-Ocean surface temperatures when
compared with the average value.
• The accepted definition is a warming or cooling of
at least 0.5°C (0.9°F) averaged over the eastcentral tropical Pacific Ocean.
• When this happens for less than five months, it is
classified as El Niño or La Niña conditions;
• if the anomaly persists for five months or longer,
it is called an El Niño or La Niña "episode.”
• Typically, this happens at irregular intervals of 2–
7 years and lasts nine months to two years.
• The first signs of an El Niño are:
• Rise in surface pressure over the Indian Ocean,
Indonesia, and Australia
• Fall in air pressure over Tahiti and the rest of the
central and eastern Pacific Ocean
• Trade winds in the south Pacific weaken or head east
• Warm air rises near Peru, causing rain in the
northern Peruvian deserts
• Warm water spreads from the west Pacific and the
Indian Ocean to the east Pacific. It takes the rain with
it, causing extensive drought in the western Pacific and
rainfall in the normally dry eastern Pacific.
• El Niño's warm current of nutrient-poor tropical water,
heated by its eastward passage in the Equatorial
Current, replaces the cold, nutrient-rich surface water
of the Humboldt Current.
• When El Niño conditions last for many months,
extensive ocean warming occurs
• Economic impact to local fishing for an international
market can be serious.
The Southern Oscillation (fluctuation) is the
atmospheric component of El Niño.
• It is an oscillation in air pressure between the
tropical eastern and the western Pacific Ocean
waters. The strength of the Southern Oscillation
(fluctuation) is measured by the Southern
Oscillation Index (SOI).
• The SOI is computed from fluctuations in the
surface air pressure difference between Tahiti
and Darwin, Australia.
• Low atmospheric pressure tends to occur over warm water
and high pressure occurs over cold water
• This is in part because deep convection over the warm
water acts to transport air.
• El Niño episodes are associated with negative values of the
SOI, meaning that the pressure at Tahiti is relatively low
compared to Darwin.
Almost a complete
reverse of El Nino
Storms and heavy
rain in Oceana
and SE Asia
Air pressure over
Tahiti (mid Pacific) is
abnormally high and
low over Australia
Westbound Trade
wind is strong,
carrying warm surface
water further west
than normal
Equatorial cloud is
split in the pacific
La Niña is the opposite phase of the El Niño-Southern Oscillation (ENSO)
cycle, with La Niña sometimes referred to as the cold phase of ENSO and El
Niño as the warm phase of ENSO
La Niña (cold)
Conditions
(December 1998)
Normal Conditions
December 1993
El Niño (warm)
Conditions
December 1997
Effects
Bleaching of Coral
• Mass bleaching events are primarily caused by elevated sea
temperatures.
• Sea temperature increases of only 1-2° C above the long
term average over an extended period of time are enough
to trigger these events.
• Mass bleaching, or regional bleaching, can be defined as
events in which entire reef tracts or regions completely
bleach.
• The isolated bleaching that occurs from sedimentation
events, disease, and pollution, although damaging, does
not reach the scale and severity of mass bleaching.
• During El Nino years, up to 40% of global Coral stocks can
be lost.
Impact
El Nino
Fires
Location
Nature of Impact
Indonesia
Drought has led to fires in Indonesia;impact on
rainforests Smoke has affected much of South East
Asia in 1987; smoke inhaled affects health
particularly of children
Dust Storms Australia
1982-83 El Nino led to dust storm that blanketed
Melbourne
Brush fires followed in the region
Biological/ South West USA Warmer Wetter weather in west USA encourages
disease
SAfrica
pests and spread of disease. E.g. ants, malaria, field
mice carrying hantavirus
LESS disease due to drier periods
Fishing
Peru
Reduction in fish stocks off coast due to loss of cold
Japan
water upwell.
Global
Reduction in Abalone (a fish) due to temp change.
California
Poultry prices increase as fish meal price increases
Warmer waters than normal can attract fish like
Marlin which benefits the sport fishing industry
Farming
SE ASIA
India and N
Australia
CHILE
Flooding/Mud Andean areas in
slides
Bolivia, Peru,
Ecuador.
West Coast and
Gulf states in the
USA
Water
Aus
supplies
SW USA
Heating
Famine and
unrest in the
population
Canada and NE
USA
Bangladesh
Drought, crop failure and affecting livestock
Failure of monsoon rains withering crops and economy
El Nino has extended growing seasons for grapes; also led
to a higher acid levels in grapes. Beneficial effects on the
aroma and taste of wines.
Warm Ocean currents in the eastern pacific increases air
temperatures and precipitation. Heavier rain fall leads to
rivers bursting banks, flooding and mudslides.
Loss of life, land and buildings. Billions of dollars lost on
agricultural and property losses in Gulf states of USA.
Many countries affected by drier conditions face acute
water shortages
In El Nino yrs, Australia has had to introduce water
conservation measures
Replenishment of Water Supplies in this usually dry area
There can be economic benefits such as lower heating
costs due to milder winters in El Nino years.
Drier conditions have contributed to crop failure and
severe shortages of food; these contributed to unrest in
malnutrition and poor health.