La Niña FAQ

What is La Niña?
"La Niña" is a Spanish term which means "the little girl", and is sometimes called "El Viejo", "anti-El Niño", or simply "the cold spell". La Niña is the apperance of water which is colder than normal in the east and central Pacific, close to Peru, and is known as the sister of El Niño, which produces warmer water than normal in this same area.

Little history is known about La Niña, but at the beginning of the 20th century, there had not yet established the relation between La Niña, and El Niño. The scientist Sir Gilbert Walker detected some similarities in the precipitation amounts in South America. Later, it lead him to formulate the assumption of other associations with these temperature and precipitation changes in Oceania, and of the atmospheric pressure in Darwin, Australia, and Tahiti. He discovered that the pressure went up in the east and down in the west. He formulated the term. "Australian Ossolation" to describe his discovery.

At the end of the 1960s, a Norwegian meteororologist, Bjerkens Jacob, established a relation between the changes of the surface sea temperature, and the strong rains which came with the low pressure. The discovery of Bjerkens have allowed the discovery that there is a relation between the warm water of El Niño and the colder water of La Niña. The combined disoveries of Walker and Bjerkens was renamed "El Niño Southern Osolation" (ENSO).

Now, it is thought that La Niña is produced because of an unusual than normal circulation of the trade winds, which are normally from the west, and push the warm surface water towards Indonesia and Oceania. For reasons still badly understood, the trade winds can be periodically reinforced, and can push colder water towards the coast of South America and reduce the temperature of the water resulting in a La Niña.

What are the effects of La Niña?
In general, the effects of La Niña are more direct and spectacular during the winter of the northern hemisphere, but of course, the effects vary around the world and the intensity can be affected by the distance from the Pacific waters. For example, British Columbia would have a better chance of seeing the results of La Niña than would Denmark.

Normally during a La Niña, this is what happens;
• the rains in the south-east of Asia are abnormally high
• dry periods in the areas of the South American desert
• abnormally strong monsoons in the Indien sub-continent
• torrential rains in the south-east of Asia
• rainy weather in eastrn Australia
• cool and wet winters in the south-east of Africa

In the United States, cold and snowy winters in the states north-west of the Great Lakes, drier than than normal in south-east, dry winters in the south-west, and an increase in the number of hurricanes and tropical storms in the states along the coast of the Atlantic.

In the Canadian Praries, there are sometimes temperatures of -30 ºC to -40 ºC, with more precipitation than normal around the country.

Normally there is a low in the Pacific just below Alaska which filters the cold air towards the south of the British Columbia. When the air passes over the ocean, it is heated, but, when it is a La Niña year, the low is not strong enough to circulate the air, so the artic air is directed to the Canadian Praries and then the remainder of Canada.

Why do these things happen?
It is thought that La Niña occurs because of a reinforcement of the normal circulation of the trade winds, which are normally from the west, and pushes water towards Oceania. This water is normaly warm, but when the water is moved, colder water from the depths of the ocean is 'upwelled' to replace the warm water, then this new colder water, is then pushed by the winds throught the Pacific.

An accumulation of colder water towards the coast of South America, causes an increase in the formation of thick convective clouds, and storms, and hurricanes devellop a very stronger force and a very different trajectory, like Hurricane Mitch in 1998, which destroyed vast regions of Honduras, Belize, and Nicaragua. The overall atmospheric changes induce temperature and precipitation changes in North America, which can last several months.

How is La Niña different from El Niño?
Yes, La Niña has a similar relation with El Niño. El Niño is almost the opposite of La Niña, it heats water of the same Pacific area, rather than cool them.

The first observation of El Niño was in 1567 by South American fishers who noticed there was unusually warm water near the east of the Pacific ocean along the equator and near the coast of Peru.

Scientists think that El Niño is caused by the same reason as La Niña, the changes in the circulation of the trade winds. El Niño occurs every 2 to 7 years or approximately every 4 years. These trade winds can sometimes be reduced or even shifted. That moves the hotter water from the coast of South America, outward along the equator into the Pacific.

Scientists believe that the effect of the water changes, can have an effect or even increase in the force and the frequency of the phenomena of El Niño, which have been observed during these last few decades.

Below there is a table of comparison which indicates in general what are happens during both phenomenons.

LA NIÑA EL NIÑO
1st Observation unknown 1567
Frequency 2 to 7 years 2 to 7 years
Temperatures diminuation increase
Precipitation increase diminuation
Humidity increase diminuation
Atmospheric
Pressure		 diminuation increase
What force does La Niña have?
All the episodes of La Niña do not have the same intensity. The force and intensity of an episode of La Niña, dependes upon the temperature of the Pacific Ocean, and direction and the circulation of the trade winds. In general, the colder the temperature of the water, with favorable winds, not too strong or weak, can help alot with devellopement of hurricanes in the Atlantic and climatic changes around the globe. In mid-May 1998 in the center of the Pacific, the water temperature was only 9 ºC, and the cold water zone extended from Peru in a long line to the Pacific with a length of more than 7000 km.

In 1988, it took only two months since the beginning of La Niña, for the water temperature of the Pacific Ocean to drop to only 4 ºC! In 1998, these same zones were twice as cold, in less time. In February 1989, an intense zone of high pressure from Alaska, moved south, causing the temperatures to plonge to -30 ºC with -40 ºC in the Canadian Praries. It was the stongest high pressure system ever recorded in North America. At Northway in Alaska, U.S.A., the atmospheric pressure reached 107.50 kPa (31.7 in. Hg), and brought snow to southern California.

In comparison to the 1995 - 1996 La Niña, the Yukon Territoiry in Canada was only 2 ºC below normal, Manitoba and Northern Ontario were nearly 6 ºC below normal, with tons of snow extending into the Great Lakes. More than 130 cm of snow fell on Lake Huron that winter, more than three and half times more than normal. Finally, British Columbia was 2 ºC to 4 ºC below that normal, with more precipitation than normal in all forms. For example, December 29th 1996 saw 64.5 cm snow fall in Victoria, pushing the total received that month to 123.9 cm of snow, a snowfall record for the day and month. Compare that to Victoria's normal December snowfall of 13.8cm.



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 Last Modified: 03 September 2005 - 23:41 GMT
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