El Niño and la Niña – a tale of two extremes
For centuries Peruvian fisherman have noticed some years that surface waters become unusually warm at Christmas time. This disruption has serious consequences for marine species, since the plankton that normally proliferate in cold waters are no longer there to support the fish on which the fishermen’s livelihood depends.
El Niño is a cyclic phenomenon occurring in the Pacific Ocean. During an El Niño, the waters off the coast of Peru, usually between 18 and 22°C, warm within the space of a few months to between 25 and 29°C.
El Niño is a cyclic phenomenon occurring in the Pacific Ocean. During an El Niño, the waters off the coast of Peru, usually between 18 and 22°C, warm within the space of a few months to between 25 and 29°C.
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The disruption is caused by a slackening of the tradewinds that normally pile up warmer water to the west of the Pacific Basin, around the Philippines. Within 2 months, this build-up of warm water covering an area equivalent to the North-American continent works its way eastward to the coast of South America. |
Fishing is not the only sector to feel the effects of El Niño. Climate is also affected across the globe, since heat and moisture interact with the atmosphere, leading to heavy rainfall, flooding in Peru and storms and tornadoes in the Central Pacific islands. Meanwhile, usually dry regions such as East Africa become wetter. On the other hand, normally rainy regions like Australia and Indonesia are ravaged by drought and wildfires.
Sometimes El Niño is followed by a reverse pattern known as La Niña, in which the tradewinds return with a vengeance, pushing the warm waters back westward. La Niña is the exact opposite of its cousin, bringing cold and drought where El Niño brought heat and rainfall.
Sometimes El Niño is followed by a reverse pattern known as La Niña, in which the tradewinds return with a vengeance, pushing the warm waters back westward. La Niña is the exact opposite of its cousin, bringing cold and drought where El Niño brought heat and rainfall.
Normal pattern :
Easterly tradewinds push surface waters in the Pacific towards Australia and the Philippines, creating a warm pool at the western end of the basin (in red on the illustration) with higher temperatures and sea level.
As the winds cross the ocean, they load up with moisture and release it as heavy rains over the warm pool.
Meanwhile, at the eastern end of the basin along the coasts of Chile and Peru, nutrient-rich cold waters well up to the surface, which is good for anchovy.
Easterly tradewinds push surface waters in the Pacific towards Australia and the Philippines, creating a warm pool at the western end of the basin (in red on the illustration) with higher temperatures and sea level.
As the winds cross the ocean, they load up with moisture and release it as heavy rains over the warm pool.
Meanwhile, at the eastern end of the basin along the coasts of Chile and Peru, nutrient-rich cold waters well up to the surface, which is good for anchovy.
When El Niño awakens
Westerly wind bursts at the eastern end of the basin allow the warm pool to drift eastward into the central Pacific. The tradewinds weaken or disappear altogether. Atmospheric convection and the storm zone move eastward with the warm pool, bringing heavy rainfall to the Central Pacific islands, and flooding along the coastal areas of western South America.
Surface waters are warmer off the coasts of Chile and Peru, so nutrients disappear and fish stocks dwindle rapidly.
Westerly wind bursts at the eastern end of the basin allow the warm pool to drift eastward into the central Pacific. The tradewinds weaken or disappear altogether. Atmospheric convection and the storm zone move eastward with the warm pool, bringing heavy rainfall to the Central Pacific islands, and flooding along the coastal areas of western South America.
Surface waters are warmer off the coasts of Chile and Peru, so nutrients disappear and fish stocks dwindle rapidly.
La Niña pattern
The tradewinds strengthen, shrinking the warm pool and cooling the Western Pacific. The climate is drier and colder off the coast of America. Atmospheric convection is confined to the western end of the basin. Rain is abundant over Indonesia. Cold waters upwell more strongly along the west coast of South America; where anchovy is plentiful.
The tradewinds strengthen, shrinking the warm pool and cooling the Western Pacific. The climate is drier and colder off the coast of America. Atmospheric convection is confined to the western end of the basin. Rain is abundant over Indonesia. Cold waters upwell more strongly along the west coast of South America; where anchovy is plentiful.
