PresentDay climate variability Objectives ENSO mode AO and

Present-Day climate variability Objectives: • ENSO mode • AO and NAO mode • PDO UNBC 1

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• Anomaly : The deviation from the mean. To calculate SST anomalies, the long-term mean for a specific point in the ocean is subtracted from the current value. A negative value indicates that the current value is cooler (smaller) than usual, while a positive value indicates that the current value is warmer (larger) than usual. For example: • The Nino 3. 4 value for December 2003 26. 9 °C • The long-term mean for the Nino 3. 4 region 26. 5 °C • Anomaly = current value - mean = 26. 9 - 26. 5 = 0. 4 UNBC 4

ENSO MODE UNBC 5

• South American fishermen have noticed the appearance of warm waters in the eastern Pacific Ocean along the coast of Ecuador and Peru. As the phenomenon typically becomes apparent around Christmas, the name "El Niño", or the Christ Child was eventually used. • La Niña: A cooling of the ocean surface off the western coast of South America, occurring periodically every 4 to 12 years and affecting Pacific and other weather patterns. UNBC 6

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• Recognizing El Niño can be seen in Sea Surface Temperature in the Equatorial Pacific Ocean UNBC 11

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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. UNBC 13

Scientists who studied El Niño • Sir Gilbert Thomas Walker • Credited with the discovery of El Niño • Identified the Walker Circulation • His findings represented invaluable steps forward UNBC 14

Scientists who studied El Niño • Dr. Klaus Wyrtki is now best known for his • ENSO research from the • 1970 s to 1993. Developing breakthroughs in understanding and forecasting El Niño • Establishing the tide gage network that provided the essential oceanographic data set. UNBC 15

Scientists who studied El Nino • UNBC Jacob Bjerknes • Took Walker’s idea of El Niño one step further and suggested that many long-term variations in the world’s climate may be due to large-scale interactions between the oceans and the atmosphere 16

• 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); (3) changes in the external forcing; (4) interactions between ENSO and the seasonal cycle UNBC 17

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• Seasonal Cycle and ENSO Is the seasonal cycle necessary for ENSO to be realized? Not likely: Many models without an annually varying sun have proven successful at simulating interannual variability that is ENSO-like. Is the seasonal cycle fundamental to the irregularity in the ENSO events? Many models are run without an annually varying sun and the ENSO events that they produce occur irregularly. However, ENSO is sufficiently tied to the annual cycle that it is useful to think of a canonical ENSO event, formed by compositing observations fixed to the calendar year. UNBC 19

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, UNBC 20

2) Wetter during June-August (JJA) in the intermountain regions of the United States and over central Chile. Drier than normal conditions generally observed over northern South America, Central America and southern Africa during DJF, and over eastern Australia during JJA. UNBC 21

La Niña UNBC 22

La Niña UNBC 23

Flooded area in Lakeport, California as a result of the 1998 El Nino event. (Federal Emergency Management Agency) UNBC 24

Bush fire in Australia as a result of the 1998 El Niño event. (Photo courtesy of Fred Hoogervirst/Panos Picture/London) UNBC 25

Temperature UNBC 26

Difference in maximum Snow depth in millimeters between El Niño and La Nina and Neutral years El ELNiño La Niña UNBC 27

The map shows typical summer precipitation response following the onset of El Niño. The numbers indicate the rate of precipitation (mm/day) by which the precipitation departs from the seasonal normal. UNBC 28

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. UNBC 29

• 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. UNBC 30

• 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. UNBC 31

• 2002 -2003: El Nino spawned storms brought damaging winds to southwestern B. C. in early January. Winds gusting over 110 km/h toppled two mobile towers, each worth about $15 million, at the shipping docks near Vancouver. UNBC 32

• 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 UNBC 33

Atmospheric circulation 1) a pronounced eastward extension of the midlatitude jet stream to the extreme eastern Pacific, and 2) an equatorward shift of the jet streams over the eastern Pacific. Overall, these conditions reflect an increasing zonally uniform distribution of both temperature and winds across the Pacific basin, and are a major factor affecting the winter weather patterns and storm tracks in the middle latitudes over both North and South America. UNBC 34

Oceanic circulation • The warm water propagates poleward along the west coast of North America by coastally trapped Kelvin waves; encounters the steep Mendocino escarpment off California (about 41 N) and is capable of propagating past the escarpment (Allen and Hsieh 1997). Propagation north of 41 N was observed during an El-Nino (Huyer and Smith 1985). UNBC 35

• Atmospheric Teleconnection PNA (Pacific-North American Pattern) AO (Arctic Oscillation) NAO (North Atlantic Oscillation) PDO (Pacific Decadal Oscillation) UNBC 36

How is ENSO currently detected and predicted? • • • Satellites provide data on tropical rainfall, wind, and ocean temperature patterns, as well as changes in conditions for hurricane formation. Ocean buoys help to monitor sea-surface and upper ocean temperatures. Radiosondes help to monitor global weather and climate patterns, and to monitor and predict El Niño and La Niña influences on U. S. weather. High-density surface data network helps to monitor and predict El Niño and La Niña influences on U. S. weather. Super computers are used to gather all of the weather data around the world and put it into useful formats used by scientists. They also run sophisticated computer models to help scientists better understand predict El Niño and La Niña. An entire suite of diagnostic and prediction tools run on high-speed computers that allow El Niño and La Niña to be monitored in near-real time. UNBC 37

• Predictions of ENSO (1) statistical models (2) dynamical models UNBC 38

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PNA PNA: 4 centers: Hawaii(20 N, 160 W); North Pacific Ocean (45 N 165 W); Alberta (55 N 115 W); and the Gulf Coast region of USA (30 N 80 W) UNBC 40

Red, black, and blue contours on the maps indicate positive, zero, and negative values, respectively UNBC 41

The PNA is associated with a Rossby wave pattern with centers of action over the Pacific and over N. America. PNA index = ½ [ Z (20 N, 160 W)-Z(45 N, 165 W) +Z(55 N, 115 W)-Z(30 N, 85 W)] UNBC 42

• 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 aboveaverage 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. UNBC 43

• 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 belowaverage totals over the upper Midwestern United States. • 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). UNBC 44

AO AO is the dominant mode of meanmonthly sea level pressure variability over the Northern Hemisphere with an out-of-phase relation between the sea level pressure over the Arctic basin and that at the midlatitudes (Thompson and Wallace 1998). UNBC 45

AO Index UNBC 46

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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. UNBC 48

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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. UNBC 51

North Atlantic Oscillation (positive) UNBC 52

• 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 UNBC 53

NAO negative phase UNBC 54

• 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 UNBC 55

• 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. UNBC 56

Typical wintertime Sea Surface Temperature (colors), Sea Level Pressure (contours) and surface wind stress (arrows) anomaly patterns during warm and cool phases of PDO • Warm phase Cold phase UNBC 57

• 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. UNBC 58

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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 • central Alaska sockeye • central Alaska pink • southeast Alaska pink - 37. 2% +242. 2% -33. 3% -38. 3% -64. 4% +220. 4% +251. 9% +208. 7% Published in the Bulletin of the American Meteorological Society 78: 1069 -1079, 1999. UNBC 61