What
is La Niņa?
Quick Facts
El
Niņo
La
Niņa is characterized by
unusually cold ocean temperatures in the equatorial Pacific.
At
the turn of this century, a connection between La Niņa, El Niņo, and
other weather patterns had yet to be established. During the 1920s, the
head of the Indian Meteorological Service, Sir Gilbert Walker, recognized
patterns to the rainfall in South America. His discovery led him to
theorize additional associations with the change in the ocean
temperatures, and with atmospheric pressure changes measured at stations
at different parts of the Pacific (Darwin, Australia, and Tahiti).
Noticing
that as pressure rises in the east, there is typically an accompanying
decrease in the west, with the reverse also true, he coined the term
Southern Oscillation to categorize his find.
Further
study led to the realization that Asian monsoon seasons under certain
barometric conditions were often linked to drought in Australia,
Indonesia, India and parts of Africa, and to mild winters in western
Canada.
Not
until the late 1960s did a Norwegian meteorologist, Jacob Bjerknes, a
professor at the University of California, establish the connection
between the changes in sea surface temperatures and the weak winds from
the east and heavy rainfall that accompany low pressure conditions.
Ultimately,
Bjerknes' discovery led to the recognition that the warm waters of El
Niņo (with the often cool waters of La Niņa) and the pressure variance
of Walker's Southern Oscillation are interrelated, leading to the full
naming of the phenomenon as : "El Niņo Southern Oscillation (ENSO)".
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Reference: Green Lane
Environment Canada
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The Phrase
"La Niņa" is Spanish for "the girl" and sometimes
called "El Viejo" (old man). It is characterized by
unusually cold ocean temperatures in the equatorial Pacific.
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La Niņas appear approximately every 4-5 years. They typically last
1-2 years.
-
Global
climate abnormalities of La Niņa are less pronounced and sometimes
tend to be different than the El Niņo - however, the effects are not
always the opposite of each other.
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It is
believed that La Niņa's cooling of the equatorial Pacific tend to favor
hurricane formation in the western Atlantic.
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La Niņa
usually brings colder winters to the Canadian west and Alaska, and
drier, warmer weather to the American Southeast.
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Reference: Green Lane
Environment Canada
