El Niño. 1 of 6. El Niño-Southern Oscillation (ENSO)

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1 This website would like to remind you: Your browser (Apple Safari 4) is out of date. Update your browser for more security, comfort and the best experience on this site. Encyclopedic Entry El Niño El Niño-Southern Oscillation (ENSO) For the complete encyclopedic entry with media resources, visit: El Niño is a climate pattern that describes the unusual warming of surface waters along the tropical west coast of South America. El Nino has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America. El Niño events occur irregularly at two- to seven-year intervals. However, it is not a regular cycle, or strictly predictable in the sense that ocean tides are. El Niño has long been recognized by fishers off the coast of Peru as the yearly appearance of unusually warm water in the Pacific Ocean. The name El Niño, meaning the "little boy" in Spanish, was used because the phenomenon often arrived around Christmas. Peruvian scientists later noted that more intense climatic changes occurred at intervals of several years, shifting the meaning of El Niño to describe these irregular and intense events rather than the annual warming of coastal surface waters. Led by the work of Sir Gilbert Walker in the 1930s, climatologists determined that El Niño occurs simultaneously with the Southern Oscillation. The Southern Oscillation is a change in atmospheric pressure over the tropical eastern and western Pacific Ocean. When coastal waters become warmer in the eastern tropical Pacific (El Niño), atmospheric pressure decreases in the eastern Pacific and increases in the western Pacific (Southern Oscillation). Climatologists define these linked phenomena as El Nino-Southern Oscillation (ENSO). Today, most scientists use the terms El Niño and ENSO interchangeably. Scientists use the Oceanic Nino Index (ONI) to measure deviations from normal sea-surface temperatures. El Niño events are indicated by sea-surface temperature increases of more than.5 degrees Celsius (.9 Fahrenheit) for at least five successive three-month seasons. The intensity of El Niño events varies from weak temperature increases about 2-3 degrees Celsius (4-5 degrees Fahrenheit) with only moderate local effects on weather and climate to very strong increases 8-10 degrees Celsius (14-18 degrees Fahrenheit) associated with worldwide climatic changes. Upwelling In order to understand the development of El Niño, its important to be familiar with non-el Niño conditions in the Pacific Ocean. Normally, strong trade winds blow west across the tropical Pacific, the region of the Pacific Ocean located between the Tropic of Cancer and the Tropic of Capricorn. These winds push warm surface water toward the west Pacific. The western Pacific Ocean borders Asia, the islands of Oceania, and Australia. Due to the warm trade winds, the sea surface is normally about.5 meter (1.5 feet) higher and 8 degrees Celsius (14 degrees Fahrenheit) warmer in Indonesia than Ecuador. The westward movement of warmer waters causes cooler waters to rise toward the surface along the coasts of Ecuador, Peru, and Chile. This process is known as upwelling. This cold upwelling elevates the thermocline, the level of ocean depth that separates warm surface water from the colder water below. Upwelling elevates this cold water, rich in nutrients, to the euphotic zone, the upper layer of the ocean. Nutrients in the cold 1 of 6

2 water include nitrates and phosphates. Tiny organisms called plankton use these nutrients for photosynthesis, the process that creates food from sunlight. Other organisms, such as clams, eat the plankton, while intermediate predators like fish or marine mammals prey on the clams. Upwelling provides food for a wide variety of marine life, and the tropical South American coastline is home to some of the world's richest fisheries. Some of the fisheries include anchovy, sardine, mackerel, shrimp, tuna, and hake. Fishing is one of the primary industries of Peru, Ecuador, and Chile. Upwelling also influences global climate. The process increases rainfall over the western Pacific's warmer waters, such as the islands of Indonesia and New Guinea. The eastern Pacific, along the coast of South America, remains relatively dry. El Niño Events During an El Niño event, westward-blowing trade winds weaken along the Equator. These changes in pressure and wind speed cause warm surface water to move eastward along the Equator, from the western Pacific to the coast of South America. The warm water builds up, or thickens, along the coasts of Ecuador, Peru, and Chile. Pushing the thermocline down as much as 152 meters (500 feet), this thick layer of warm water does not allow for normal upwelling to occur. Without this upwelling of nutrient-rich cold water, the euphotic zone of the eastern Pacific can no longer support its normally productive ecosystem. Fish populations die or migrate. El Niño has a devastating impact on the Ecuadorian and Peruvian economies. El Niño also produces widespread and sometimes severe changes in climate. Rainfall increases drastically in Ecuador and northern Peru, which normally have fairly arid climates. Coastal flooding and erosion are common El Niño events. Rains and floods may destroy homes, schools, hospitals, and businesses. They also limit transportation and destroy crops. As El Niño brings rain to South America, it brings droughts to Indonesia and Australia. These droughts threaten water supplies, as local reservoirs dry up and rivers carry less water. Agriculture, which depends on water for irrigation, is threatened. Stronger El Niño events also disrupt global atmospheric circulation. Global atmospheric circulation is the large-scale movement of air that helps distribute thermal energy across the surface of the Earth. The eastward movement of oceanic and atmospheric heat sources causes unusually severe winter weather at the higher latitudes of North and South America. Heavy rain along Central America's Pacific coast is common in El Niño years. Regions as far north as the U.S. states of California and Washington may experience longer, colder winters because of El Niño. El Niño has diverse impacts on tropical storms in the Pacific and Atlantic. Most meteorologists think El Niño events contribute to more tropical storms in the eastern Pacific, while contributing to a reduced number of hurricanes in the Atlantic and Gulf of Mexico. El Niño events of and were the most intense of the 20th century. During the event, sea-surface temperatures in the eastern tropical Pacific were many degrees above normal. These strong temperature increases caused severe climatic changes: Australia experienced harsh drought conditions; typhoons devastated Tahiti; and record rainfall and flooding hit central Chile. The west coast of North America was unusually stormy during the winter season, and fish catches were dramatically reduced from Chile to Alaska. The El Niño event of is regarded as the strongest of the 20th century. This was the first El Niño event to be scientifically monitored from beginning to end. The event produced severe drought conditions in Indonesia, Malaysia, and the Philippines. Peru experienced very heavy rains and severe flooding. In the United States, increased winter rainfall hit California, while the Midwest experienced record-breaking warm temperatures during a period known as "the year without a winter." In addition to increased natural hazards and economic devastation, health crises are also associated with El Niño events. Diseases carried by mosquitoes and flies, such as dengue fever and malaria, increase as warmer, more humid weather expands mosquitoes habitat. 2 of 6

3 'Flavors' of El Niño The transition period of an El Niño event is called a "Trans Niño." Trans Niño events occur at the onset and closing of an El Niño event. Trans Niño events include increased tornado activity in the American Midwest. Another "flavor" of El Niño is the Modoki Niño. Modoki is a Japanese word meaning "similar, but different." Modoki Niño, also called the Central Pacific Niño, is characterized by changes in sea-surface temperatures in the central, not eastern, Pacific. Some Modoki Niño events are distinct from traditional El Niño events, such as increased hurricane activity in the Atlantic and Gulf of Mexico. Many meteorologists are critical of the Modoki Niño, calling for more climate models to study the proposed phenomenon. Monitoring El Niño Scientists, governments, and non-governmental organizations (NGOs) collect data about El Niño using a number of technologies. The National Oceanic and Atmospheric Administration (NOAA), for instance, operates a network of scientific buoys. These buoys measure ocean and air temperature, humidity, and the strength of currents and winds. The buoys are positioned at about 70 locations in the southern Pacific Ocean, from the Galapagos Islands to Australia. These buoys transmit data daily to researchers and forecasters around the world. Using data from the buoys, along with satellite imagery, scientists are able to more accurately predict El Niño and visualize its development and impact around the globe. VOCABULARY Term Part of Speech Definition agriculture the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching). annual adjective yearly. arid adjective dry. atmospheric circulation atmospheric pressure large-scale movement of air that helps distribute thermal energy (heat) on the surface of the Earth. force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth. buoy floating object anchored to the bottom of a body of water. Buoys are often equipped with signals. climate all weather conditions for a given location over a period of time. climatologist person who studies long-term patterns in weather. coast edge of land along the sea or other large body of water. crop agricultural produce. current steady, predictable flow of fluid within a larger body of that fluid. data plural (singular: datum) information collected during a scientific study. devastate verb to destroy. disease a harmful condition of a body part or organ. disrupt verb to interrupt. drought period of greatly reduced precipitation. 3 of 6

4 economic adjective having to do with money. ecosystem community and interactions of living and nonliving things in an area. El Nino irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean. El Nino-Southern Oscillation (ENSO) climate pattern in which coastal waters become warmer in the eastern tropical Pacific (El Nio), and atmospheric pressure decreases at the ocean surface in the western tropical Pacific (Southern Oscillation). Equator imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude. erosion act in which earth is worn away, often by water, wind, or ice. euphotic zone upper zone of the ocean. This zone goes down to approximately 600 feet. Also called the epipelagic or sunlit zone. fishery industry or occupation of harvesting fish, either in the wild or through aquaculture. flood overflow of a body of water onto land. forecast verb to predict, especially the weather. habitat environment where an organism lives throughout the year or for shorter periods of time. humidity amount of water vapor in the air. hurricane tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region. intermediate predator in a food chain or food web, an organism that eats (preys on) herbivores or other first-order consumers, but is preyed upon by top predators. interval time period between events or activities. irrigation watering land, usually for agriculture, by artificial means. latitude distance north or south of the Equator, measured in degrees. marine adjective having to do with the ocean. marine mammal an animal that lives most of its life in the ocean but breathes air and gives birth to live young, such as whales and seals. meteorologist person who studies patterns and changes in Earth's atmosphere. Midwest area of the United States consisting of the following states: Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin. migrate verb to move from one place or activity to another. monitor verb to observe and record behavior or data. National Oceanic and Atmospheric Administration (NOAA) U.S. Department of Commerce agency whose mission is to "understand and predict changes in climate, weather, oceans, and coasts; to share that knowledge and information with others, and; to conserve and manage coastal and marine ecosystems and resources." 4 of 6

5 natural hazard event in the physical environment that is destructive to human activity. NGO non-governmental organization. nitrate type of salt used as fertilizer. Excess nitrates can choke freshwater ecosystems. nutrient substance an organism needs for energy, growth, and life. Oceanic Nino Index set of data used by scientists to measure the differences in normal sea surface temperatures. phenomenon an unusual act or occurrence. phosphate type of salt used as fertilizer. Excess phosphates can choke freshwater ecosystems. photosynthesis process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars. plankton plural (singular: plankton) microscopic aquatic organisms. predictable adjective regular or able to be forecasted. primary adjective first or most important. reservoir natural or man-made lake. satellite imagery photographs of a planet taken by or from a satellite. scientist person who studies a specific type of knowledge using the scientific method. simultaneously adverb at the same time. Southern Oscillation decrease in the air pressure over the tropical eastern and western Pacific Ocean, linked to El Nino. successive adjective following in order. temperature degree of hotness or coldness measured by a thermometer with a numerical scale. thermal energy heat, measured in joules or calories. thermocline level or layer of a fluid depth where temperature changes more rapidly than the fluid either above or below it. tide rise and fall of the ocean's waters, caused by the gravitational pull of the moon and sun. tornado a violently rotating column of air that forms at the bottom of a cloud and touches the ground. trade wind winds that blow toward the Equator, from northeast to southwest in the Northern Hemisphere and from southeast to northwest in the Southern Hemisphere. transmit verb to pass along information or communicate. transportation movement of people or goods from one place to another. tropical adjective existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south. typhoon tropical storm with wind speeds of at least 74 miles (119 kilometers) per hour. Typhoons are the same thing as hurricanes, but usually located in the Pacific or Indian Ocean region. 5 of 6

6 upwelling process by which currents bring cold, nutrient-rich water to the ocean surface. visualize verb to make visual. weather state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness. For Further Exploration Articles & Profiles National Geographic Magazine: El Niño Nature's Vicious Cycle NOAA: El Niño Theme Page FAQs Websites NOAA: NOAA's El Niño Page National Geographic Society. All rights reserved. 6 of 6

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