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La Niña: Canadian Perspective
Wind, water and temperature are part of an intricate set of connected elements
that affect weather patterns around the globe. Weather events half-way around
the world can affect local forecasts. Perhaps the most striking examples of
weather phenomena affecting global climate are El Niño and La Niña.
Environment Canada scientists are tracking the 1998-99 La Niña. In Canada,
La Niña can bring considerable fluctuations in weather patterns. However,
most La Niña winters tend to be colder and snowier than normal.
Most of the prediction models are indicating that the easterly trade winds
in the tropics would strengthen. This will intensify the up-welling of cold
waters in the eastern Pacific. A moderate strength La Niña is possible
during the winter of 1998-99, but considerable uncertainty remains about the
timing and strength of the event. The response of the global atmospheric circulation
and its effects on Canadian winter weather conditions is even more uncertain.
What is La Niña?
La Niña is an extensive cooling of the central and eastern Pacific Ocean.
La Niña is also characterized by climate conditions that are sometimes
opposite to those of El Niño (which brings warm ocean temperatures
in the equatorial Pacific).
La Niña occurs when easterly trade winds in the tropics strengthen,
intensifying the up-welling of cold waters off the coast of Peru and Ecuador.
During La Niña, sea surface temperature can fall as much as 4 °C
below normal.
The effects of La Niña are strongest during the Northern Hemisphere
winter. While La Niña occurs less frequently than El Niño, weather
patterns over North America associated with La Niña tend to be more
variable.
During La Niñas snowfall is abundant from the interior of British Columbia
to the Great Lakes region. In the United States, winters are warmer and drier
than normal in the Southeast and cooler and wetter than normal in the Northwest.
How does this year's La Niña compare with other La Niñas?
In May, water temperatures in the eastern tropical Pacific showed a rapid
transition from El Niño to La Niña like conditions. The water
temperatures dropped by 8 °C to reach 2-3 °C below normal in a few
weeks. Since mid June however, there has been little change. Recent satellite
imagery from NASA indicates that warm waters from the 1997-98 El Niño
continues to linger in parts of the eastern tropical Pacific and raises questions
about the strength and timing of the emerging La Niña. Since 1976,
there have been considerably fewer La Niñas compared to El Niños
- the previous strong La Niña occurred 10 years ago (1988-89).
What are La Niña's global impacts?
The effects of La Niña are generally more direct and dramatic during
the Northern Hemisphere winter. La Niñas may also affect weather patterns
in other parts of the world, sometimes causing abnormally high rainfall in
Southeast Asia and dry conditions in the desert areas of South America. Some
impacts of previous La Niñas include the following:
-
The Indian subcontinent received extremely heavy monsoon rains.
-
Southeast Asia was lashed by torrential rains.
-
Southeastern Africa experienced cool and wet winters.
-
Eastern Australia received above normal rainfall.
-
In the United States, northern states west of the Great Lakes experienced
cold, snowy winters. The Southwest had high temperatures and low precipitation.
There was an increased threat of hurricane activity in the mid-Atlantic
states and winters in Alaska were unusually cold.
What has been the impact of previous La Niñas in Canada?
There have been 17 moderate-to-strong La Niñas since the 1900's. Each
La Niña has its own unique characteristics, affecting Canada's weather
patterns in different ways. These are some major weather events from the last
two La Niñas in Canada.
La Niña 1995-96:
- Much of Canada suffered from a particularly long winter. Furthermore,
from late October to March, many southern area locations had continuous
snow cover.
- Winter temperatures were 11 °C below normal in Winnipeg - the second
coldest winter on record. Temperatures did not climb above -20 °C
for over a week and the overnight lows plummeted below -30 °C for
19 days in a row.
- The long-lived cold also affected Calgary. Residents were told to turn
on their taps around the clock after weeks of cold weather caused pipes
to freeze.
La Niña 1988-89:
- A drastic change occurred in the weather across the nation in February
as an intense high pressure area over Alaska plunged southward causing
record-breaking cold temperatures. Temperatures on the Prairies ranged
from -30 °C to -40 °C.
- Cold Arctic air even reached the west coast of British Columbia, producing
the longest cold spell of any February in Vancouver (January 31 to February
15) with minimum temperatures remaining below 0 °C. Fruit trees were
damaged. Frigid air pushed as far south as Southern Texas and snow even
blanketed Southern California.
- From mid-January, bitterly cold air poised over the Yukon intensified
and produced record breaking low temperatures. At Old Crow, the temperatures
remained below -40 °C for over a week.
- A build-up of bitterly cold air mass in the Northwest Arctic helped to
produce the highest atmospheric pressure reading in North America. At
Northway Alaska, the highest pressure reading of 107.5 kilopascals was
recorded in February. A few days later, an all-time record high pressure
reading was set in Saskatchewan and Manitoba.
- Central and Atlantic Canada also felt the frigid weather. Many localities
in the Maritimes recorded the coldest February in over a decade.
Average winter conditions during past La Niñas
• The numbers indicate degrees Celsius by which the temperatures
depart from normal.
• Environment Canada's official forecast for the 1998-99 winter can be
viewed at http://weatheroffice.ec.gc.ca/saisons/index_e.html
Is there a link between climate change and La Niña?
Scientists are questioning whether climate change influences changes in climate
associated with El Niño or La Niña. There is no consensus yet
on any direct link. However, scientists are pursuing further research in order
to provide confident answers to these questions.
Quick facts
- The phrase "La Niña" is Spanish for "the girl".
Sometimes called "El Viejo"
(old man), La Niña is characterized by unusually cold ocean temperatures
in the equatorial Pacific.
- La Niñas appear approximately every 4-5 years and typically last
1-2 years.
- Global climate abnormalities of La Niña are less pronounced and
in some areas tend to be the opposite of those associated with El Niño.
However, the effects of La Niña are not always opposite to that
of El Niño.After an El Niño, the climate does not always
swing to a La Niña phase. There have been only 17 La Niñas
compared to 25 El Niños since the turn of the century.
- La Niña is a natural phenomenon in the climate system that has
been occurring for centuries. Detailed observations from ships led to
reliable record keeping in the earlier half of this century.
- It is believed that La Niña's cooling of the equatorial Pacific
tends to favour the development of tropical storms and hurricanes in the
Atlantic. In contrast, El Niño conditions tend to suppress the
development of hurricanes in the Atlantic, but increase the number of
tropical storms over the eastern and central Pacific Ocean.
For Further Information
Amir Shabbar
Environment Canada
(416) 739-4435
La Niña Web site : http://www.tor.ec.gc.ca/lanina/
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Created :
2002-08-23
Modified :
2002-12-18
Reviewed :
2002-12-18
Url of this page : http://www.msc.ec.gc.ca
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