La Niña is a climate pattern that describes the cooling of surface ocean waters along the tropical west coast of South America. La Nina is considered to be the counterpart to El Nino, which is characterized by unusually warm ocean temperatures in the equatorial region of the Pacific Ocean. 
 
Together, La Niña and El Niño are the "cold" (La Niña) and "warm" (El Niño) phases of the El Nino-Southern Oscillation (ENSO). ENSO is series of linked weather- and ocean-related phenomena. Besides unusually warm or cool sea-surface temperatures, ENSO is also characterized by changes in atmospheric pressure.
 
La Niña events sometimes follow El Niño events, which occur at irregular intervals of about two to seven years. The local effects on weather caused by La Niña ("little girl" in Spanish) are generally the opposite of those associated with El Niño ("little boy" in Spanish). For this reason, La Niña is also called anti-El Niño and El Viejo (the old man in Spanish). 
 
Scientists use the Oceanic Nino Index to measure the deviations from normal sea-surface temperatures that El Niño and La Niña produce in the east-central Pacific Ocean. La Niña events are indicated by sea-surface temperature decreases of more than .5 degrees Celsius (.9 degrees Fahrenheit) for at least five successive three-month seasons. 
 
La Niña is caused by a build-up of cooler-than-normal waters in the tropical Pacific, the area of the Pacific Ocean between the Tropic of Cancer and the Tropic of Capricorn. Unusually strong, eastward-moving trade winds and ocean currents bring this cold water to the surface, a process known as upwelling. 
 
Upwelling can cause a drastic drop in sea-surface temperature. Coastal sea-surface temperatures near Ecuador and Peru dropped nearly 4 degrees Celsius (7 degrees Fahrenheit) during the 1988-89 La Niña event. 
 
Effects of La Niña 
 
Both El Niño and La Niña affect patterns of rainfall, atmospheric pressure, and global atmospheric circulation. Atmospheric circulation is the large-scale movement of air that, together with ocean currents, distributes thermal energy on the surface of the Earth. These changes are the main sources of variability in climate for many areas worldwide. 
 
La Niña is characterized by lower-than-normal air pressure over the western Pacific. These low-pressure zones contribute to increased rainfall. 
 
Rainfall associated with the summer monsoon in Southeast Asia tends to be greater than normal, especially in northwest India and Bangladesh. This generally benefits the Indian economy, which depends on the monsoon for agriculture and industry.
 
However, strong La Niña events are associated with catastrophic floods in northern Australia. The 2010 La Niña event correlates with one of the worst floods in the history of Queensland, Australia. More than 10,000 people were forced to evacuate, and damage from the disaster was estimated at more than $2 billion.
 
La Niña events are also associated with rainier-than-normal conditions are over southeastern Africa and northern Brazil. 
 
La Niña is also characterized by higher-than-normal pressure over the central and eastern Pacific. This results in decreased cloud production and rainfall in that region. Drier-than-normal conditions are observed along the west coast of tropical South America, the Gulf Coast of the United States, and the pampas region of southern South America.
 
La Niña usually has a positive impact on the fishing industry of western South America. Upwelling brings cold, nutrient-rich waters to the surface. Nutrients include plankton eaten by fish and crustaceans. Higher-level predators, including high-value fish species such as sea bass, prey on the crustaceans. 
 
La Niña events may last between one and three years, unlike El Niño, which usually lasts no more than a year. Both phenomena tend to peak during the Northern Hemisphere winter. 
 
Monitoring La Niña
 
Scientists collect data about El Niño and La Niña using a number of technologies. The National Oceanic and Atmospheric Administration (NOAA), for instance, operates a network of buoys which measure sea-surface temperature, air temperature, currents, winds, and humidity. The buoys are located in about 70 locations, from the Galapagos Islands to Australia. These buoys transmit data to researchers and meteorologists every day.
 
Using buoy data in conjunction with visual information they receive from satellites, scientists are able to more accurately predict ENSO and visualize its development and impact around the globe.
La Niña
La Niña is associated with rainy weather in Australia and Indonesia, and cooler sea-surface temperatures off the coast of South America.

Kicking Up Dust
The impacts of La Niña on our weather and climate have been highly variable throughout history. La Niña delivers drier, warmer, and sunnier weather along the southern tier of the United States, from California to Florida. This weather increases the risk of wildfires in Florida and dryness in the North American plains. The great Dust Bowl drought of the 1930s is thought to have been caused by a decade of La Niña-like conditions and was likely responsible, in part, for the severe drought in the American Midwest in 1988. The 1988-89 La Niña, believed to be one of the most severe in history, has been estimated to cost $40 billion in damages in North America!

abundant
Adjective

in large amounts.

Noun

the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

atmospheric circulation
Noun

large-scale movement of air that helps distribute thermal energy (heat) on the surface of the Earth.

Noun

force per unit area exerted by the mass of the atmosphere as gravity pulls it to Earth.

buoy
Noun

floating object anchored to the bottom of a body of water. Buoys are often equipped with signals.

catastrophic
Adjective

very bad.

characterize
Verb

to describe the characteristics of something.

Noun

all weather conditions for a given location over a period of time.

Noun

visible mass of tiny water droplets or ice crystals in Earth's atmosphere.

conjunction
Noun

combination of items, events, or ideas.

correlate
Verb

to bring different sets of data into order, or establish a relationship or connection between them.

crustacean
Noun

type of animal (an arthropod) with a hard shell and segmented body that usually lives in the water.

Noun

steady, predictable flow of fluid within a larger body of that fluid.

data
Plural Noun

(singular: datum) information collected during a scientific study.

drastic
Adjective

severe or extreme.

economy
Noun

system of production, distribution, and consumption of goods and services.

Noun

irregular, recurring weather system that features a warm, eastern-flowing ocean current in the eastern Pacific Ocean.

El Nino-Southern Oscillation (ENSO)
Noun

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).

equatorial
Adjective

having to do with the equator or the area around the equator.

evacuate
Verb

to leave or remove from a dangerous place.

Noun

overflow of a body of water onto land.

Noun

amount of water vapor in the air.

indicate
Verb

to display or show.

industry
Noun

activity that produces goods and services.

Noun

weather system that includes cool ocean temperatures in the eastern Pacific Ocean.

meteorologist
Noun

person who studies patterns and changes in Earth's atmosphere.

Noun

seasonal change in the direction of the prevailing winds of a region. Monsoon usually refers to the winds of the Indian Ocean and South Asia, which often bring heavy rains.

National Oceanic and Atmospheric Administration (NOAA)
Noun

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."

Noun

substance an organism needs for energy, growth, and life.

Oceanic Nino Index
Noun

set of data used by scientists to measure the differences in normal sea surface temperatures.

Pampas
Noun

flat grasslands of South America.

phenomena
Plural Noun

(singular: phenomenon) any observable occurrence or feature.

plankton
Plural Noun

(singular: plankton) microscopic aquatic organisms.

predator
Noun

animal that hunts other animals for food.

satellite
Noun

object that orbits around something else. Satellites can be natural, like moons, or made by people.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

thermal energy
Noun

heat, measured in joules or calories.

trade wind
Noun

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.

tropical
Adjective

existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

Noun

process in which cold, nutrient-rich water from the bottom of an ocean basin or lake is brought to the surface due to atmospheric effects such as the Coriolis force or wind.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.