El NiñoLa Niña

El Niño - Southern Oscillation

phenomenon that takes place in the central and eastern equatorial Pacific

characterized by an interaction between the ocean and the atmosphere and their combined effect on climate

effects of a band of sea surface temperatures which are anomalously warm or cold for long periods of time that develops off the western coast of South America and causes climatic changes across the tropics and subtropics

The three phases of the El Niño – Southern Oscillation (ENSO)

• trade winds blow east to west across the surface of the

tropical Pacific Ocean

Neutral Phase

• trade winds weaken or may even reverse, allowing the area

of warmer than normal water to move into the central and

eastern tropical Pacific OceanEl Niño

• the Walker Circulation intensifies with greater

convection over the western Pacific and stronger trade winds

La Niña

Convection

Walker Circulation

Upwelling

process generally associated with warm rising air and the formation of cloud

named after Sir Gilbert Walker, the scientist who first recognized a semi-regular pattern of high and low rainfall over India.

a vertical motion of water

wind or currents displace water at the surface of the ocean, water from deeper in the ocean is drawn up to replace the displaced water

Trade Winds

Thermocline

a wind blowing steadily toward the equator from the northeast in the northern hemisphere or the southeast in the southern hemisphere

an oceanic water layer in which water temperature decreases rapidly with increasing depth

Warm sea surface temperatures in the western Pacific pump heat and moisture into the atmosphere above.

Through atmospheric convection, this warm air rises high into the atmosphere and if moist enough, causes towering cumulonimbus clouds and rain.

Air then travels east before descending over the cooler eastern tropical Pacific.

Ocean temperatures, tropical precipitation, and wind patterns are near average conditions during this phase.

Neutral Phase

Neutral Phase

These warmer than normal ocean temperatures are associated with a deepening of the thermocline in the central to eastern Pacific.

There is a weaker upwelling of cooler ocean waters from below.

Associated with a band of warmer than average ocean water temperatures that periodically develops off the Pacific coast of South America.

Causes the ocean surface to be warmer than average, as upwelling of cold water occurs less or not at all.

El Niño

El Niño

The pool of warmer water is confined to the far western tropical Pacific, resulting in warmer than usual sea surface temperatures in the region north of Australia.

Sea surface temperatures across the central and eastern tropical Pacific Ocean become cooler than usual.

Thermocline moves closer to the surface – cool waters from the deep ocean are drawn to the surface as upwelling strengthens.

La Niña

La Niña

Effects of El Niño

Ocean dynamical processes depress the thermocline in the eastern and central equatorial Pacific, and along the coasts of North and South America.

The supply of nutrients to the euphotic zone drops or may be cut off entirely. Zooplankton that feed on phytoplankton decrease in abundance. Fish, sea birds and marine mammals die off or migrate to more

productive regions in search of food. Undernourished sea birds and marine mammals may experience

reproductive failures or abandon young when food becomes scarce.

El Niño can also cause bleaching of tropical corals when water temperatures become too warm. Occurred during 1998 in the Galapagos Islands, off the coast of

Panama, in the Great Barrier Reef of Australia and elsewhere in the tropics in response to the exceptionally strong 1997–1998 El Niño.

Decadal warming trends in tropical ocean temperatures contributed to this bleaching

Effects of El Niño

Coral Bleaching

El Niño can also dramatically affect fisheries. Example would be the collapse of the Peruvian anchoveta fishery following

the 1972–1973 El Niño. Intense fishing pressure and extraordinarily high mortality rates during the

1972–1973 El Niño caused the fishery to crash.

Flood-contaminated water supplies in some regions contributed to outbreaks of cholera and dysentery.

Stagnant pools of floodwater also provided ideal breeding grounds for mosquitoes and other insects that spread infectious diseases.

Effects of El Niño

El Niño 1997-1998 Philippines according to UNCCD (United Nations Convention to Combat Desertification) in 2000 Depletion of palay production.

• 3,832,000 hectares available for rice planting to 3,017,000 hectares

• Almost 17% of plantation area was not used. 1992 drought in Mindanao

• 8 months of drought• 27,389 hectares of Watershed areas were burned

Massive Land Erosion• 45.6% land Degradation of total lands

Effects of El Niño

It affects tropical storm frequency, intensity, and geographical distribution Depletion of palay production. Through changes in sea surface temperature and atmospheric

circulation.

Hurricanes 1995 Atlantic hurricane season

• That year witnessed a bumper crop of 19 named tropical Atlantic storms, including 11 hurricanes, almost double the usual number.

Effects of La Niña

Hurricane Mitch• One of the strongest Atlantic hurricanes on record and the

deadliest in 200 years. • Spawned during the 1998 La Niña. • Devastated Central America, claiming 10 000 lives, leaving over

three million homeless, and causing US$6 billion in damage.

Effects of La Niña

Hurricane Mitch

For instance, higher monsoon rainfall totals over the Indian subcontinent, the western Pacific, and northeastern Brazil can support greater agricultural production and economic growth.

In terms of marine ecosystems, primary productivity, driven by more intense equatorial and coastal upwelling, is generally enhanced.

Enhanced winter snowpack in the mountains of the Pacific Northwest provide for extra hydroelectric power production, ample summer water supplies, and improved freshwater habitat for salmon.

Benefits of La Niña

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