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Presentation schedule:Dec 2, Wed: Dec 4, Friday

Sidjak, Rob Hart, IreneClarke, Steve Jackson, IanBerry, Kathryn Martin, SarahCosway, Katryn Paterson, GraemeEarl, Gareth Priestley, DanEnns, Deborah deHoog, Neil

Talk: 10-13 mins. Questions: 1-3 mins. (The last Quiz will be in next Friday).

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Present-Day climate variability

Objectives:•ENSO mode

•AO and NAO mode

•PDO

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ENSO MODE

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ENSO• A scientific definition of ENSO events: When the

three-month running mean of the SST anomalies in the Nino 3.4 region are greater than or equal to 0.5°C, there is a good chance of an El Niño event taking place. When the anomalies are smaller than or equal to -0.5°C, there is a good chance of a La Niña event taking place.

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•Recognizing El NiñoEl Niño can be seen in Sea Surface Temperature in the Equatorial Pacific Ocean

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•El Niño Years:

1902-1903  1905-1906   1911-1912  1914-1915 1918-1919  1923-1924   1925-1926  1930-1931 1932-1933  1939-1940   1941-1942  1951-1952 1953-1954  1957-1958   1965-1966  1969-1970 1972-1973  1976-1977   1982-1983  1986-1987 1991-1992  1994-1995   1997-1998 2002-2003

2006-2007

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•Irregularity of ENSO  (1) noise internal to either the atmosphere

or ocean (2) inherent nonlinearity of the coupled

atmosphere/ocean system (or in the coupling itself);

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Effect of ENSO on Climate

• In the Tropics, El Niño episodes are associated with increased rainfall across the east-central and eastern Pacific and with drier than normal conditions over northern Australia, Indonesia and the Philippines. Elsewhere, wetter than normal conditions tend to be observed 1) during December-February (DJF) along coastal Ecuador, northwestern Peru, southern Brazil, central Argentina, and equatorial eastern Africa,

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Flooded area in Lakeport, California as a result of the 1998 El Nino event. (Federal Emergency Management Agency)

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Bush fire in Australia as a result of the 1998 El Niño event. (Photo

courtesy of Fred Hoogervirst/Panos Picture/London)

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La Niña

El Niño

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• What are the effects of an El Nino on Canada? During the winter of an El Nino event, the air temperature

tends to be warm over most of Canada, with the greatest warming centerd around Manitoba-western Ontario. Southern Canada also tends to be drier during an El Nino winter. Southern British Columbia tends to receive less snow.

In the case of the cold La Nina event-- the opposite of the warm El Nino event-- the coastal waters off British Columbia tend to be cool. In a La Nina winter, the Canadian air temperature (especially west of Quebec) tends to be below normal, while the precipitation in southern Canada tends to be above normal. Southern British Columbia tends to receive more snow.

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Significant impacts of ENSO on Canadian natural resources and environment have been documented in a variety of areas including water resources, agriculture, forestry, fisheries, power utilities, coastal zones and other climate sensitive sectors of the Canadian economy.

(1) the fishery of British Columbia.

(2) forestry … Hsieh and Tang, 2001. Interannual variability of accumulated snow in the Columbia basin, British Columbia. Water Resources

Res. 37: 1753-1760.

Hsieh, W.W., B. Tang and E.R. Garnett, 1999. Teleconnections between Pacific sea surface temperatures and

Canadian prairie wheat yield. Agricul. Forest Meteorol. 96: 209-217.

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• During El Nino, as the sea surface temperature (SST) is above normal off B.C., the returning Fraser River sockeye salmon (with yearly landed value of about $600 million) favor traveling via the northern route of Johnstone Strait instead of the more commonly used southern route of Juan de Fuca Strait. Many fishermen with fishing permits on the west coast of Vancouver Island suffered heavy losses in 1997 as the sockeye bypassed their area.

• Other impacts occur in forestry. During El Nino, temperatures in the BC interior, especially in winter, are above normal and summer precipitation is typically below normal. Mountain pine beetle and forest fires are the two major natural disturbance agents in interior forests. A warm winter climate is favorable to mountain pine beetle survival and has recently led to a severe increase in lodgepole pine mortality. At the same time fire risk increase under warm and dry summer conditions.

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•1997-1998: El Niño induced mild weather helped to significantly reduce motor vehicle accidents on B.C. roads. The ICBC reported that it enjoyed a substantial economic benefit this winter. The insurance corporation realized a saving of $3 million per day owing to the mild winter weather.

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•How can sea surface temperatures in the tropical Pacific Ocean have any bearing on the weather that occurs in northern America?

i) Atmospheric circulation ii) Oceanic Circulation iii) Atmospheric teleconnection

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•Predictions of ENSO

(1) statistical models (2) dynamical models

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PNA (Pacific-North American Pattern) AO (Arctic Oscillation) NAO (North Atlantic Oscillation) PDO (Pacific Decadal Oscillation)

•Atmospheric Teleconnection

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PNA: 4 centers: Hawaii(20N,160W);North Pacific Ocean (45N 165W); Alberta (55N 115W); and the Gulf Coast region of USA (30N 80W)

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The PNA is associated with a Rossby wave pattern with centers of action over the Pacific and over N. America.

PNA index = ½ [ Z (20N,160W)-Z(45N,165W) +Z(55N, 115W)-Z(30N, 85W)]

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•PNA is one of the most prominent modes of low-frequency variability in the Northern Hemisphere extratropics. The positive phase of the PNA pattern features above-average heights in the vicinity of Hawaii and over the intermountain region of North America, and below-average heights located south

of the Aleutian Islands and over the southeastern United States.

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• The positive phase of the PNA pattern is associated with above-average temperatures over western Canada and the extreme western United States, and below-average temperatures across the south-central and southeastern U.S. The PNA tends to have little impact on surface temperature variability over North America during summer. The associated precipitation anomalies include above-average totals in the Gulf

of Alaska extending into the Pacific Northwestern United States, and below-average totals over the upper Midwestern United States.

Buys Ballot's law

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• Although the PNA pattern is a natural internal mode of climate variability, it is also strongly influenced by the El Niño/ Southern Oscillation (ENSO) phenomenon. The positive phase of the PNA pattern tends to be associated with Pacific warm episodes (El Niño), and the negative phase tends to be associated with Pacific cold episodes (La Niña).

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AO is the dominant mode of mean-monthly sea levelpressure variability over the Northern Hemisphere withan out-of-phase relation between the sea level pressure over the Arctic basin and that at the mid-latitudes (Thompson and Wallace 1998).

AO

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AO Index

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•What is the NAO ? Sometimes AO is also referred to as the

North Atlantic Oscillation (NAO) due to its strong manifestation over the Atlantic sector.

A large-scale mode of natural climate variability having large impacts on weather and climate in the North Atlantic region and surrounding continents.

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•The NAO is the dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia. The NAO is a large scale seesaw in atmospheric mass between the subtropical high and the polar low. The corresponding index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting several years.

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•Positive NAO Index The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low.

• The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland

The eastern US experiences mild and wet winter conditions

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• Negative NAO Index

• The negative NAO index phase shows a weak subtropical high and a weak Icelandic low.

• The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway.

• They bring moist air into the Mediterranean and cold air to northern Europe

• The US east coast experiences more cold air outbreaks and hence snowy weather conditions.

• Greenland, however, will have milder winter temperatures

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•PDO (Pacific Decadal Oscillation)

PDO is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years.

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•Warm phase Cold phase

Typical wintertime Sea Surface Temperature (colors),  Sea Level Pressure (contours) and surface wind stress (arrows) anomaly patterns during warm and cool phases of PDO

 

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Percent change in mean catches of four Alaskan salmon stocks following major PDO sign changes in 1947 and 1977.  salmon stock 1947 step 1977 step

• western Alaska sockeye - 37.2% +242.2%• central Alaska sockeye -33.3% +220.4%• central Alaska pink -38.3% +251.9%• southeast Alaska pink -64.4% +208.7%

Published in the Bulletin of the American Meteorological Society 78: 1069-1079, 1999.

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•Fisheries scientist Steven Hare coined the term "Pacific Decadal Oscillation" (PDO) in 1996 while researching connections between Alaska salmon production cycles and Pacific climate. PDO has since been described as a long-lived El Niño-like pattern of Pacific climate variability because the two climate oscillations have similar spatial climate fingerprints, but very different temporal behavior.