Flavors of Climate variability: El Nino, La Niña, Recurring Jet Stream patterns, Multi-Decadal Variability

By

Dr. Gerry Bell Climate Prediction Center (CPC)

NOAA/National Weather Service/ National Centers for Environmental Prediction

Presented to Community Collaborative Rain, Hail and Snow Network (CoCoRaHS)

17 January 2013

www.cpc.ncep.noaa.gov

Outline

1. Dinstinguishing weather and climate, climate variability

2. Climate variability linked to El Niño and La Niña (ENSO)

3. Climate variability linked to recurring jet stream patterns (Teleconnections) • Some concepts • Pacific/ North American Pattern (PNA) • North Atlantic Oscillation (NAO) • Arctic Oscillation (AO)

4. Climate variability linked to decadal ocean patterns

• Atlantic Multi-Decadal Oscillation (AMO) • Pacific Decadal Oscillation (PDO)

5. Summary

What is Weather?

Weather: Short-term (hourly to daily) changes in temperature, humidity, precipitation, wind, etc. Weather is what the TV weatherman talks about. Examples: Thunderstorms, winter storms, hurricanes, tornadoes, a short-term flood event, cold/warm fronts, a sunny or rainy day, etc.

Hurricane Katrina

www.squidoo.com/thunderstorm-pictures.

www.accuweather.com.

Thunderstorm Snowstorm

A weather forecast showing predicted fronts and rainfall.

Another daily weather forecast.

Climate, Climate Variability, and Climate Change

Climate: Average or slowly varying aspects of atmosphere-ocean system. (e.g., Annual mean conditions, the four seasons, monsoons, hurricane season, average temperature changes throughout the year, day-night temperature cycle, etc.)

Climate Variability: Variations in the average state of the climate due to natural

processes (recurring patterns of ocean temperature, tropical rainfall, jet stream winds, etc.).

Climate Change: Variations in either the mean state of the climate or in its

variability, which is attributed directly or indirectly to human activity (global warming due to increasing CO2 concentrations)

Weather: Daily temperatures

Climate: 30-year average daily temperature

Climate Variability: A cool summer

Example Daily Temperatures

Climate Variability

•Climate variability typically occurs over vast distances (continental, hemispheric, global), with time scales ranging from weeks to years to decades.

•Climate variability is often linked to recurring jet stream, ocean temperature, and tropical rainfall patterns.

•Climate variability differs throughout the world and with the seasons.

Atlantic Multi-Decadal Oscillation

El Niño El Niño Impacts

African Sahel Drought 2009-2010 Record

Snowfall

Atlantic Hurricane Season Strength

Some examples of climate variability:

Inde

x of

Atla

ntic

Oce

an

Tem

pera

ture

Dep

artu

res

Sea surface temperature Departures

Climate Variability Linked to El Niño and La Niña (ENSO)

El Niño and La Niña •El Niño and La Niña represent extremes in the El Niño/ Southern Oscillation (ENSO), a leading source of year-to-year climate variability.

•Discovered  in  stages:  Peruvian  fisherman,  Sir  Gilbert  Walker  (1920’s),  Jacob  Bjerknes (1960’s).

•Related to changes in tropical Pacific Ocean temperatures; Occur roughly every 3-5 years, typically last 9-12 months.

•El Niño: a warming of the central and eastern equatorial Pacific •La Niña: a cooling of the central and eastern equatorial Pacific

•NOAA classifies El Niño and La Niña episodes using the Oceanic Niño Index (ONI). •ONI=3-month running mean of SST departures in the Niño 3.4 region (east-central equatorial Pacific)

Monitoring and Predicting El Niño and La Niña (ENSO) www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ensocycle/enso_cycle.shtml

El Niño/ La Niña Tutorial

U.S. Impacts by Season Temperature Precipitation Snow

U.S. Temperature and Precipitation Distributions Weekly ENSO Evolution, Status, and Prediction Presentation

Monthly EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION

Recent Model Forecasts Official ENSO Probability Forecast

Normal Ocean Surface Temperatures (°C) January

Equator

Date Line

Equatorial ocean temperatures are normally warmest in the western Pacific and coolest in the eastern Pacific. Tropical rainfall is normally strongest in the Western Pacific/ Indonesia region, and non-existent over the equatorial cold tongue.

Warm, Wet Cool, Dry

˚C

Equatorial Cold Tongue

January Ocean Temperatures (oC) Comparing Normal to El Niño

Temperature Departures Temperatures El Niño

Normal

•El Niño: a warming of the central and eastern equatorial Pacific

January Ocean Temperatures (oC) Comparing Normal to La Niña

Temperature Departures Temperatures La Niña

Normal

•La Niña: a cooling of the central and eastern equatorial Pacific

Wintertime Tropical Rainfall (Inches)

Wetter Drier

Strong El Nino

•El Niño and La Niña produce massive re-distributions of rainfall across the tropical Pacific Ocean.

•This subsequently alters the Pacific jet stream, resulting in mid-latitude climate variability across the North Pacific Ocean and North America.

4 8 12 16 20

Wetter Drier

Strong La Nina

La Niña Deep tropical convection and Pacific jet stream retracted westward toward Asia.

4 8 12 16 20 El Niño

Deep tropical convection and Pacific jet stream extend across the central and eastern Pacific.

Pacific Jet Stream Pacific Jet Stream

Scales show Inches of Rain

Normal Jet Normal Jet

December- March

June-August

Mid-latitude impacts stronger in winter hemisphere

El Niño impacts include: • Temperature and precipitation patterns • Jet streams and storm tracks • Monsoons and hurricanes

Global El Niño Temperature and Precipitation Impacts

Global La Niña Temperature and Precipitation Impacts

December- March

June-August

Mid-latitude impacts stronger in winter hemisphere

La Niña impacts include: • Temperature and precipitation patterns • Jet streams and storm tracks • Monsoons and hurricanes

El Niño Winter Impacts: North Pacific and North America

•The Pacific jet stream is directly influenced by tropical convection patterns. •El Niño strengthens and extends this jet stream and its storm track eastward, •Affects winter weather across the North Pacific Ocean and North America.

7

El Niño: Persistent, extended Pacific jet stream and amplified storm track

La Niña Winter Impacts: North Pacific and North America

8

•La Niña weakens the Pacific jet stream and makes it much more variable, often shifting it back toward Asia. •The polar jet steam is also shifted westward. •Affects winter weather across the North Pacific Ocean and North America.

La Niña: Weaker and Variable Pacific Jet Stream

El Niño and La Niña Hurricane Season Impacts

More Less

Less More

No Change

No Change

More Less

Less More

Less More

More= More hurricanes Less= Fewer hurricanes Red text refers to El Niño signal. Blue text refers to La Niña signal.

11

Climate Variability Linked to Recurring Jet Stream Patterns (Teleconnections)

Recurring Jet Stream Patterns Another Important Source of Climate Variability

•Jet streams (rivers of strong winds at about 35,000 ft altitude) are associated with very large patterns of air pressure, wind, storminess, precipitation, and temperature. •Much climate variability is linked to recurring jet stream patterns, which influence air pressure, wind, temperature, and precipitation patterns across vast distances (across ocean basins, across a continent, etc.). These inter-related patterns are called Teleconnections.

El Niño Impacts El Niño and La Niña

produce teleconnections across  the  America’s.

Air Pressure Patterns

H

Winds flow clockwise around areas of High Pressure

L

Winds flow counter-clockwise around areas of Low Pressure

H

Air Pressure, Temperature and Precipitation Relationships

L

Air Pressure and Wind Relationships

Colder, Drier Warmer, Wetter Warmer

Clear Weather Stormier, Warm and Cold fronts

Jet Streams and Air Pressure

Jet Streams are associated with a 4-celled pressure pattern.

High Pressure

Jet Core

Low Pressure

Jet Stream

High Pressure

Low Pressure

Lines of Equal Pressure

Jet Stream and Air Pressure Relationships

Changes in jet stream position and strength are associated with corresponding changes in this pressure pattern - a jet stream related teleconnection pattern.

Jet Streams, Precipitation and Storms

Jet Core Jet Stream Storms

Form Here

Storms Decay Here

Jet streams influence regions of storm formation/ decay

Jet Stream and Storm Relationships

Jet Streams produce a 4-celled pattern of wet/dry

Jet Core Dry

Wet Dry

Jet Stream Wet

Jet Stream and Precipitation Relationships

Lines of Equal Pressure

Jet stream variability also produces these teleconnection patterns.

Putting It All Together

Jet stream-related patterns of air pressure, storminess, precipitation, and temperature can span vast distances. What  we  see  as  “Whacky  Weather”  (such  as  might  be  gleaned  from  this  schematic), can simply be jet stream-related teleconnection patterns.

Jet Stream, Pressure, Temperature, Precipitation, Storm Relationships

Wetter, Warmer

Jet Core

Cooler, Drier Storms

Decay here

Drier

Jet Stream

High Pressure

Low Pressure

Low Pressure

High Pressure

Lines of Equal Pressure

Wetter, Storms

Form here

Average Winter Jet Streams, Air Pressure, Storminess

L

L

H

H

L H

L H

Pacific Jet Stream Atlantic Jet Stream

Jet Stream

•The sheer scale of the two main jet streams is evident, along with high pressure (H) and low pressure (L) areas, and areas of storm formation.

•Fluctuations in strength and location of the Pacific and Atlantic jet streams produce several teleconnection patterns that affect the North Pacific, North America, the North Atlantic, and Eurasia. We already saw some of these impacts with El Niño and La Niña.

Lines of Equal Pressure

Storm Formation Region

Teleconnections: Monthly Monitoring at CPC www.cpc.ncep.noaa.gov/data/teledoc/telecontents.shtml

Air Pressure Patterns Precipitation Patterns

Temperature Patterns Historical Time Series (1950-Pres)

SomeTeleconnection Patterns

Recent Monthly Index Values

Teleconnections: Daily Forecasts at CPC www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/teleconnections.shtml

Daily Indices and Forecasts

Average Winter Jet Streams, Air Pressure, Storminess

L

L

H

H

L H

L H

Pacific Jet Stream Atlantic Jet Stream

Jet Stream

Lines of Constant Pressure

Storm Formation Region

Pacific/ North American (PNA) Pattern

Pacific jet stream and region of storm formation shift eastward to western U.S. (as during El Niño)

Positive Phase of PNA Pattern Negative Phase of PNA Pattern

Pacific jet stream and region of storm formation shifts westward toward Asia (as during La Niña).

January Jet Stream and Air Pressure Departures

Pacific Jet Stream

Higher pressure Lower pressure

Pacific Jet Stream Storm Formation Region

Pacific Jet Stream

Related to changes in position and strength of the Pacific jet stream.

The PNA pattern produces climate variability across the North Pacific Ocean and North America. It is sometimes linked to El Niño and La Niña.

Pacific/ North American (PNA) Pattern Winter vs. Summer

Higher Pressure

Lower Pressure

Warmer

Colder

Wetter

Drier

•Correlation patterns reflect sign of anomalies for positive phase of PNA pattern.

•Wintertime impacts are stronger than in summer.

Correlation With Surface Air Pressure

Correlation With Surface Temperature

Correlation With Precipitation

Pacific/ North American (PNA) Pattern Negative Phase

Higher Pressure

Lower Pressure

Warmer

Colder

Wetter

Drier

Air Pressure Departures

Surface Temperature Departures

Precipitation Departures

Pacific/ North American (PNA) Pattern Index Time Series: 3-Month Running Means

The PNA pattern varies from weeks to months to years, and produces climate variability across the North Pacific Ocean and North America.

North Atlantic Oscillation (NAO) Related to North-South Fluctuations in North Atlantic Jet Stream

The NAO varies from weeks to years to decades, producing climate variability extending from central North America to Eurasia and Africa.

Smoothed NAO Index Back to 1860

http://www.ldeo.columbia.edu/res/pi/NAO/

Wintertime NAO Index 1950-Present

Warm, Wet

Cold, Dry Warmer, Less snow

Cold, Dry

Warm, Wet

Colder, Snowier

Warm

Cold

North Atlantic Oscillation (NAO)

Higher Pressure

Lower Pressure

Warmer

Colder

Wetter

Drier

Correlation With Surface Air Pressure

Correlation With Surface Temperature

Correlation With Precipitation

•Correlation patterns reflect sign of anomalies for positive phase of PNA pattern.

•Wintertime impacts are stronger than in summer.

North Atlantic Oscillation (NAO): Negative Phase

Higher Pressure

Lower Pressure

Warmer

Colder

Wetter

Drier

Surface Air Pressure Departures

Surface Temperature Departures

Precipitation Departures

El Niño and Negative NAO

El Niño Only

oC

Winter El Niño – NAO Temperature Composites

El Niño and Positive NAO

•Understanding combinations of climate signals is important.

•El Niño impacts can vary depending on NAO and other climate factors (AMO, PDO).

•Take care when performing regression analysis on individual climate factors.

Wintertime Arctic Oscillation (AO)

Higher pressure Lower pressure

•The AO reflects air mass exchange between polar region and middle latitudes. •AO affects Pacific and North Atlantic jet streams and storm tracks. •AO produces hemispheric-scale climate variability, with largest impacts extending from the North Pacific Ocean to Eurasia

Positive Phase Negative Phase

Weaker Aleutian Low

Stronger Aleutian Low

Weaker Icelandic

Low

Stronger Icelandic

Low

Normal Atlantic jet stream

AO-related Pacific and Atlantic jet stream

Contains aspects of PNA and NAO patterns

Arctic Oscillation (AO): U.S. Winter Impacts

Positive AO

Negative AO

Warmer

Colder

Fewer Nor’easters

More  Nor’easters More cold-air outbreaks

Increased Snowfall

More heavy rain events

Frequent warm-ups

More rain, clouds

Stronger Winds, Waves

More Ice, snow

Less rain And clouds

The AO varies from weeks to years to decades, producing hemispheric climate variability. Many impacts are similar to PNA and NAO patterns.

Climate Variability Linked to Decadal Ocean Patterns

•Atlantic Multi-Decadal Oscillation (AMO) •Pacific Decadal Oscillation (PDO)

The Atlantic Multi-Decadal Oscillation (AMO)

Sea Surface Temperature Departures (oC) During June-August 1995-2011

•Reflects changes in Atlantic Ocean temperatures occurring on time scales of 25-40 years. •Discovered in 1920 by Sir Gilbert Walker •Affects Indian Monsoon, west African monsoon, Atlantic hurricane activity.

Map depicts warm phase of AMO

˚C

Observed AMO Index

Jun.-Sep. West Central India Rainfall Departures

Jun.-Sep. African Sahel Rainfall Departures

The Atlantic Multi-Decadal Oscillation (AMO) and Monsoon Rainfall in India and Western Africa

This AMO-Related Pattern Increases Atlantic Hurricane Activity for Decades at a time

Warmer Wet

Warmer

High-activity eras for Atlantic hurricanes are associated with these conditions. Low-activity eras have opposite departures from normal.

ACE index shows the overall strength of the hurricane season. Multi-decadal fluctuations in season strength are clearly evident.

The Pacific Decadal Oscillation (PDO)

Observed PDO Index

Sea Surface Temperature Departures (Shading)

•Reflects changes in Pacific Ocean temperatures in both the tropics and higher latitudes occurring on time scales of decades. •Discovered in 1996 by Fisheries scientist Steven Hare •Predominant source of inter-decadal climate variability across Pacific Ocean

Positive Phase Negative Phase

Can Reinforce El Niño Can Reinforce La Niña

Summary

Climate Variability linked to recurring jet stream patterns PNA, NAO, other teleconnection patterns

• Seasonally dependent, continental scale, Vary months to seasons to decades (NAO).

Arctic Oscillation (AO):

• Combines parts of PNA and NAO • Hemispheric temperature and precipitation impacts.

Climate Variability linked to ocean temperature fluctuations • El Niño/ La Niña: Global impacts, strongest in winter hemisphere • North Atlantic: Atlantic multi-decadal oscillation (AMO). • North Pacific: Pacific Decadal Oscillation (PDO).

Combining these climate signals is very important for making seasonal predictions.

Questions?