UNBC 1

Present-Day climate variability

Objectives:

•ENSO mode

•AO and NAO mode

•PDO

UNBC 2

UNBC 3

UNBC 4

• 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 5

ENSO MODE

UNBC 6

• 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 7

UNBC 8

UNBC 9

UNBC 10

UNBC 11

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

UNBC 12

UNBC 13

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 14

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 15

Scientists who studied El Niño • Dr. Klaus Wyrtki is now

best known for his• ENSO research from the

1970s to 1993.

•Developing breakthroughs in understanding and

forecasting El Niño • Establishing the tide

gage network that provided the essential oceanographic data set.

UNBC 16

Scientists who studied El Nino• 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

UNBC 17

•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 18

UNBC 19

• 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 20

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 21

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 22

La Niña

UNBC 23

La Niña

UNBC 24

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

UNBC 25

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

courtesy of Fred Hoogervirst/Panos Picture/London)

UNBC 26

Temperature

UNBC 27

Difference in maximum Snow depth in millimeters between El Niño and La

Nina and Neutral years

El Niño

La Niña

EL Niño

UNBC 28

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 29

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 30

• 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 31

•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 32

•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 33

•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 34

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.

Atmospheric circulation

UNBC 35

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 41N) and is capable of propagating past the escarpment (Allen and Hsieh 1997). Propagation north of 41N was observed during an El-Nino (Huyer and Smith 1985).

UNBC 36

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

•Atmospheric Teleconnection

UNBC 37

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 and 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 38

•Predictions of ENSO

(1) statistical models

(2) dynamical models

UNBC 39

UNBC 40

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

PNA

UNBC 41

Red, black, and blue contours on the maps indicate positive,

zero, and negative values, respectively

UNBC 42

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)]

UNBC 43

•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.

UNBC 44

• 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.

• 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 45

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

UNBC 46

AO Index

UNBC 47

UNBC 48

•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 49

UNBC 50

UNBC 51

•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 52

North Atlantic Oscillation (positive)

UNBC 53

•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 54

NAO negative phase

UNBC 55

• 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 56

•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 57

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 58

•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 59

UNBC 60

UNBC 61

Percent change in mean catches of four Alaskan salmon stocks following major PDO sign changes in 1947 and 1977.  salmon stock1947 step1977 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.