La Niña Information

Introduction

This page deals with another weather phenomenon, La Niña. La Niña is very different from El Niño but there are some obvious similarities between the two. What is La Niña? provides a basic definition of this phenomenon and a picture of the anomaly. What does La Niña mean gives the Spanish translation of the name. La Niña's global climatic impact describes how La Niña's impact is felt. How does La Niña form? provides a the steps involved in the creation of a La Niña. 1998-99 La Niña? discusses the possibility of a La Niña event this year, and Chart of La Niñas since 1925 gives the dates of past La Niñas.

What is La Niña?

La Niña is the cold counterpart of El Niño, meaning sea surface temperatures in the tropical Pacific drop below normal. La Niñas form after some, but not all, El Niños, and therefore occurs less frequently than El Niño.

Picture of 1988/89 La Niña where the blue represents below average temperatures

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What does La Niña mean?

La Niña means "The Little Girl" and has a variety of names. La Niña, El Viejo, and anti-El Niño all refer to this cold event.

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La Niña's global climatic impact

La Niña's impact on climate is about the opposite of El Niño's impact. Like El Niño, La Niña's impact is best seen during winter. During a La Niña winter, winter temperatures are warmer in the Southeast while temperatures are cooler from the Great Lakes to the Pacific Northwest. Winters in the Northeast and Middle Atlantic vary. For example, the 1988 La Niña has been tied, although inconclusively, to floods in Bangladesh and droughts in the Midwest.

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How does La Niña form?

La Niña can only form after an El Niño. During an El Niño, types of waves, not beach waves, but massive movements of energy through water, are formed. They are Kelvin waves and Rossby waves. As Kelvin waves are formed, they push cold water down, which initially causes the ocean to warm. At the same time, another series of waves, Rossby waves, also form under water. They roll towards Asia and Australia. When the waves hit the coast, they reverse and head back towards South America. As the Rossby waves return, they leave cold water closer to the surface. If they bring back just enough cold water, the ocean temperatures return to normal, but sometimes they bring back to much, causing a La Niña after an El Niño.

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1998-99 La Niña?

Many of the models which correctly predicted that EL Niño would weaken by May, also predicted that it would be followed by a La Niña. As this year's El Niño weakens, there are already indications that it will lead to a La Niña.

Beginnings of the possible 1998-99 La Niña

As can be seen from the picture above, there is already a pool of cold water forming on the equator in El Niño's wake. If a La Niña does actually form, it would most likely be weak. One reason for this is that powerful La Niñas in the past have already begun to cool water in the Pacific by June. As of June, water temperature is still above average. Also, following the 1982/83 El Niño, a weak La Niña was present. Therefore, expect the impact of a weak La Niña in the winter.

Chart of La Niñas since 1925:

A year is defined as cold phase from October of that year to September of the next. For example, 1988 means a cold phase from October 1988 to September 1989.

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