El Nino is a shift in ocean temperatures and atmospheric conditions in the tropical Pacific that disrupts weather around the world. It is a poorly understood recurrent climatic phenomenon that primarily affects the Pacific coast of South America, but has dramatic impacts on weather patterns all over the world

What is El Niño - Southern Oscillation (ENSO)? El Niño is an excellent example of the interaction between the ocean and the atmosphere and there combined effect on climate. El Niño is a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. This condition results in redistribution of rains with flooding and droughts. Along the equator, the western Pacific has some of the world's warmest ocean water, while in the eastern Pacific, cool water wells up, carrying nutrients that support large fish populations. Every two to seven years, strong westward-blowing trade winds subside, and warm water slowly moves back eastward across the Pacific, like water shifting in a giant bathtub. The warm water and shifting winds interrupt the upwelling of cool, nutrient-rich water. Fish die; climatic changes affect many parts of the world. Peruvians named this phenomenon El Niño, for the Christ child, because it first appears around Christmas.

Why El Niño occurs? Normal conditions El Niño conditions

El Nino is thought to occur due to changes in the normal patterns of trade wind circulation. Normally, these winds move westward, carrying warm surface water to Indonesia and Australia and allowing cooler water to upwell along the South American coast. For reasons not yet fully understood, these trade winds can sometimes be reduced, or even reversed. This moves warmer waters toward the coast of South America and raises water temperatures. Warmer water causes heat and moisture to rise from the ocean off Ecuador and Peru, resulting in more frequent storms and torrential rainfall over these normally arid countries.

Normal Conditions El Niño Conditions Illustration of the changes in upper-level jet stream patterns over the Pacific, which typically occur during El Niño episodes. Normal flow toward the northwestern United States is deflected northward toward the Canadian and Alaskan coasts. At the same time, a secondary southern storm track appears that increases the probability of storm systems affecting the California coast, and increases the potential for storms to form in the Gulf of Mexico (Wallace and Vogel, 1994).   http://www.cimms.ou.edu/ibhs.html

The animation follows the evolution of sea level (the undulating surface) and sea-surface temperature (color) for a Warm event followed by a Cold event as simulated by the numerical model of Battisti(1988).

The relatively small motions in sea level shown here (10 - 20 centimeters) are indicative of much larger motions in the opposite direction in the depth of the thermocline below the surface. (Thermocline animation) Vertical displacements of the thermocline are particularly important along the equator in the eastern half of the Pacific basin, where they control the availability of cold water that can reach the surface through the process known as upwelling. For example, when the sea level is low, the thermocline tends to be shallow, indicating that unusually cold water is near the surface. Upwelling motions can then bring this cold water to the surface, resulting in cold conditions. When the sea level is high the situation is reversed, with cold water lying too deep to reach the surface. The result is a warm event. www.cdc.noaa.gov/ENSO/enso.description.html

During El Niño conditions, high pressure conditions develop over the western Pacific Ocean and South East Asia and the high pressure area over the Easter Islands diminishes.  As a result of these changes, the pressure difference across the Pacific Ocean becomes smaller.  This results in a decrease in the force of the trade winds.   http://www.atmosphere.mpg.de/enid/2__Circulation_Systems/__Worksheet_4_4c1.html

Anticipating, Alerting, Protecting http://www.jason.oceanobs.com/html/applications/enso/nino_prevoir_uk.html

El Niño around the world, 1997-98 Climatic effects of El Niño (Crédits D.Ducros)          Dry     Warm     Wet     Hurricane     El Niño around the world, 1997-98 http://www.jason.oceanobs.com/html/applications/enso/nino1997-98_uk.html

El Nino Scenario http://www.icess.ucsb.edu/esrg/geos/el_nino.html

Galapagos Islands (located in equatorial Pacific Ocean)

The El Niño phenomenon centers on the Galapagos Islands in the eastern tropical Pacific Ocean. It is a common phenomenon in this area of the world occurring unpredictably every three to ten years.

Major ocean currents on Earth circulate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere .

Galapagos is in the path of a cold current (the Peru or Humboldt Current), coming from Antarctica, up the coast of South America. It is also in an area that has significant seasonal upwelling. Upwelling brings deep, nutrient rich, bottom water to the surface, which enhances marine productivity. The tops of the Galapagos Islands show through the dense cloud cover during an El Niño.

The Galapagos Islands are usually very dry and desert-like (left, Halbach photo) but during El Niños the rainfall may increase so much that the islands can not absorb the water and it runs off the islands (right).

The effects of El Niño in Galapagos island

Prepared by: Mary France Padilla Marciniza Manabat N2