El Niño, La Niña, & ENSO By emma pappas

What are El Niño, La Niña and ENSO?

El Niño is an irregularly occurring and complex series of climatic changes affecting the equatorial Pacific region and beyond every few years, characterized by the appearance of unusually warm, nutrient-poor water off northern Peru and Ecuador, typically in late December.

► Abnormally warm sea surface temperatures from the date line (180W) east to the South American coast

► Changes in the distribution of tropical rainfall from the eastern Indian Ocean east to the tropical Atlantic

► Changes in sea level pressure throughout the global Tropics (low-index phase of the Southern Oscilla- tion)

► Large-scale atmospheric circulation changes in the Tropics and portions of the extratropics in both hemispheres.

La Niña is a cooling of the water in the equatorial Pacific that occurs at irregular intervals and is associated with widespread changes in weather patterns complementary to those of El Niño, but less extensive and damaging in their effects.

La Niña episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific.


El Niño-Southern Oscillation (ENSO) cycle is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific (approximately between the International Date Line and 120 degrees West).

How do El Niño, La Niña, and ENSO form?

During El Niño, warm surface water appears farther east and is spread over a broader area. Weak Highs form east and west of the Low, and surface and upper level winds are both weaker than normal. The thermocline is deeper and flatter overall, making average sea level of the eastern Pacific higher than normal.

La Niña episodes are characterized by the westward shift of warm water. This produces stronger Highs and Lows, with stronger than normal surface and upper level winds. Warm water is abnormally deep in the western Pacific and abnormally shallow in the eastern Pacific. The slope of the thermocline becomes steeper, and sea level is higher than normal in the west and lower than normal in the east.

The strong trade winds that would normally cause the deep ocean water to rise off of the coast of South America are weakened during an El Niño event. The exact cause of the weakened trade winds is unknown; however, scientists have noticed an oscillation of water surface temperatures in the Pacific ocean, referred to as the El Niño Southern Oscillation.

Contrasting conditions of El Niño and La Niña

How do El Niño , La Niña, and ENSO impact the world, United States, and Indiana?

Impact of El Niño

El Niño conditions influence wintertime atmospheric flow across the eastern North Pacific and North America (USA). In general, El Niño results in increased precipitation across California and the southern tier of states, and decreased precipitation in the Paci c Northwest and in the Ohio and Tennessee Valleys. A milder than normal winter across the northern states and western Canada is also a common effect. During the warm season, El Niño in uences hurricane development, resulting in more eastern Paci c hurricanes and fewer Atlantic hurricanes. Indiana has less precipitation and dry.

Impact of La Niña

La Niña conditions tend to influence wintertime atmospheric flow across the eastern North Pacific and North America. Seasonal precipitation impacts are generally opposite to those of El Niño. During La Niña winters, large portions of central North America experience increased storminess, and an increased frequency of significant cold-air outbreaks, while the southern states experience less storminess and precipitation. There also tends to be considerable month-to-month variations in temperature, rainfall, and storminess across central North America during the winter and spring seasons, in response to the more variable atmospheric circulation throughout the period. In the summer and autumn, La Niña can in uence hurricane development, often resulting in fewer eastern Paci c hurricanes and more Atlantic hurricanes. Indiana is more wet.

ENSO appears to be a necessary mechanism for maintaining long-term global climate stability by transporting heat from the Tropics to the higher latitudess from fluctuating ocean temperatures in the equatorial Pacific. Eventually, the surface ocean temperatures will respond to the warming of the sub-surface temperatures, and a warm phase of the ENSO cycle ensues.

What instruments & information do atmospheric scientists use to study El Nino, La Nina, and ENSO?

One of the primary indicators of ENSO events, Sea Surface Temperature (SST), is closely monitored throughout the Pacific Ocean, including Niño 3.4, a region stretching along the equator from 170W to 120W longitude and from 5N to 5S latitude. An index for monitoring and assessing the oceanic state of ENSO, known as the Oceanic Niño Index (ONI), is based on this region and represents the sea surface temperature departure from a long-term average.

NOAA operates a network of 70 stationary buoys in the equatorial Pacific, called the Tropical Atmosphere/ Ocean (TAO) array, which provides data about upper- ocean and sea surface conditions. Other important data come from satellites, radiosondes, and the high-density U.S. surface data network.

Satellite of National Oceanic and Atmospheric Administration (NOAA)

Over the years, several NASA missions have studied the effects associated with La Niña and El Niño, such as changes in sea-surface temperature (SST) and cloud cover using operational satellites.

When was Indiana last affected by El Nino, La Nina, or ENSO? Explain the local effects.

El Niño: For Indiana, temperatures typically are above average and precipitation is below average. Went into the spring of 2016.

La Niña: Early spring of 2012, causes colder and stormier than average conditions across the North for Indiana.

La Nina represents the cool phase of the El Nino/Southern Oscillation (ENSO) cycle, El Niño being the warm phase and affecting Indiana in ways mentioned above.

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