Download Flavors of Climate variability: El Nino, La Niña, Recurring Jet Stream

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.
Thunderstorm
Snowstorm
www.squidoo.com/thunderstormpictures.
A weather forecast showing
predicted fronts and rainfall.
Hurricane Katrina
www.accuweather.com.
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.)
Example Daily Temperatures
Weather: Daily temperatures
Climate:
30-year average daily temperature
Climate Variability:
A cool summer
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)
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.
Some examples of climate variability:
Index of Atlantic Ocean
Temperature Departures
Atlantic Multi-Decadal Oscillation
El Niño
Sea surface temperature Departures
Atlantic Hurricane
Season Strength
El Niño Impacts
African Sahel Drought
2009-2010 Record
Snowfall
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
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
El Niño/ La Niña Tutorial
http://www.cpc.ncep.noaa.gov/product
s/analysis_monitoring/ensocycle/enso
_cycle.shtml
Recent Model Forecasts
Official ENSO
Probability Forecast
Normal Ocean Surface Temperatures (°C)
January
Equator
Warm, Wet
Cool, Dry
Date Line
˚C
Equatorial Cold Tongue
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.
January Ocean Temperatures (oC)
Comparing Normal to El Niño
Normal
Temperatures
El Niño
Temperature Departures
•El Niño: a warming of the central and eastern equatorial Pacific
January Ocean Temperatures (oC)
Comparing Normal to La Niña
Normal
Temperatures
La Niña
Temperature Departures
•La Niña: a cooling of the central and eastern equatorial Pacific
Wintertime Tropical Rainfall (Inches)
Strong La Nina
Strong El Nino
Pacific Jet Stream
Pacific Jet Stream
Normal Jet
Normal Jet
Drier
Wetter
Wetter
Drier
Scales show
Inches of Rain
4
8
12
16
20
El Niño
Deep tropical convection and
Pacific jet stream extend across
the central and eastern Pacific.
4
8
12
16
20
La Niña
Deep tropical convection and
Pacific jet stream retracted
westward toward Asia.
•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.
Global El Niño Temperature and Precipitation Impacts
DecemberMarch
Mid-latitude
impacts
stronger in
winter
hemisphere
June-August
El Niño impacts include:
• Temperature and precipitation patterns
• Jet streams and storm tracks
• Monsoons and hurricanes
Global La Niña Temperature and Precipitation Impacts
DecemberMarch
Mid-latitude
impacts
stronger in
winter
hemisphere
June-August
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
El Niño: Persistent, extended Pacific
jet stream and amplified storm track
•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
La Niña Winter Impacts:
North Pacific and North America
La Niña: Weaker and Variable
Pacific Jet Stream
•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.
8
El Niño and La Niña Hurricane Season Impacts
More
Less
Less
More
No Change
Less More
More Less
No Change
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
Air Pressure and Wind Relationships
Winds flow clockwise around
areas of High Pressure
Winds flow counter-clockwise
around areas of Low Pressure
H
L
Air Pressure, Temperature and Precipitation Relationships
Stormier, Warm and Cold
fronts
Clear Weather
Warmer
H
Colder, Drier
L
Warmer,
Wetter
Jet Streams and Air Pressure
Jet Stream and Air Pressure Relationships
Lines of
Equal
Pressure
Low
Pressure
JetStream
Core
Jet
High
Pressure
High
Pressure
Low
Pressure
Jet Streams are associated with a 4-celled pressure pattern.
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 Stream and Precipitation Relationships
Dry
Wet
JetStream
Core
Jet
Wet
Dry
Jet Streams produce a 4-celled pattern of wet/dry
Lines of
Equal
Pressure
Jet Stream and Storm Relationships
Storms
Decay
Here
Storms
JetStream
Core Form Here
Jet
Jet streams influence regions of storm formation/ decay
Jet stream variability also produces these teleconnection patterns.
Putting It All Together
Jet Stream, Pressure, Temperature, Precipitation, Storm Relationships
Cooler, Drier
Storms
Decay here
Low
Pressure
JetStream
Core
Jet
Wetter,
Warmer
High Pressure
Wetter,
Storms
Form here
Drier
High Pressure
Lines of
Equal
Pressure
Low
Pressure
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.
Average Winter Jet Streams, Air Pressure, Storminess
Lines of
Equal
Pressure
L
Jet Stream
H
Pacific Jet Stream
H
L
H
L
H
L
Atlantic Jet Stream
Storm Formation Region
•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.
Teleconnections: Monthly Monitoring at CPC
www.cpc.ncep.noaa.gov/data/teledoc/telecontents.shtml
SomeTeleconnection Patterns
Air Pressure Patterns
Precipitation Patterns
Recent Monthly Index Values
Temperature Patterns
Historical Time Series (1950-Pres)
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
Lines of
Constant
Pressure
L
Jet Stream
H
Pacific Jet Stream
H
L
H
L
H
L
Atlantic Jet Stream
Storm Formation Region
Pacific/ North American (PNA) Pattern
Related to changes in position and strength of the Pacific jet stream.
January Jet Stream and Air Pressure Departures
Positive Phase of PNA Pattern
Pacific Jet Stream
Negative Phase of PNA Pattern
Pacific Jet
Stream
Higher pressure
Pacific Jet Stream
Pacific jet stream and region of storm
formation shift eastward to western U.S.
(as during El Niño)
Lower pressure
Storm Formation Region
Pacific jet stream and region of storm
formation shifts westward toward Asia
(as during La Niña).
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
Correlation With Surface Air Pressure
•Correlation
patterns reflect
sign of
anomalies for
positive phase
of PNA pattern.
Higher
Pressure
Lower
Pressure
Correlation With Surface Temperature
•Wintertime
impacts are
stronger than in
summer.
Warmer
Colder
Correlation With Precipitation
Wetter
Drier
Pacific/ North American (PNA) Pattern
Negative Phase
Air Pressure Departures
Higher
Pressure
Lower
Pressure
Surface Temperature Departures
Warmer
Colder
Precipitation Departures
Wetter
Drier
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
Wintertime NAO Index 1950-Present
Cold
Warm, Wet
Cold, Dry
Warmer,
Less snow
Smoothed NAO Index Back to 1860
Warm
Cold, Dry
Warm, Wet
Colder,
Snowier
http://www.ldeo.columbia.edu/res/pi/NAO/
The NAO varies from weeks to years to decades, producing climate variability
extending from central North America to Eurasia and Africa.
North Atlantic Oscillation (NAO)
Correlation With Surface Air Pressure
•Correlation
patterns reflect
sign of
anomalies for
positive phase of
PNA pattern.
Higher
Pressure
Lower
Pressure
Correlation With Surface Temperature
•Wintertime
impacts are
stronger than in
summer.
Warmer
Colder
Correlation With Precipitation
Wetter
Drier
North Atlantic Oscillation (NAO): Negative Phase
Surface Air Pressure Departures
Higher
Pressure
Lower
Pressure
Surface Temperature Departures
Warmer
Colder
Precipitation Departures
Wetter
Drier
Winter El Niño – NAO Temperature Composites
El Niño Only
•Understanding combinations of
climate signals is important.
•El Niño impacts can vary
depending on NAO and
other climate factors (AMO,
PDO).
El Niño and
Negative NAO
•Take care when performing
regression analysis on individual
climate factors.
El Niño and
Positive NAO
oC
Wintertime Arctic Oscillation (AO)
Contains aspects of PNA and NAO patterns
Positive Phase
Negative Phase
Weaker
Icelandic
Low
Stronger
Icelandic
Low
Weaker
Aleutian
Low
Stronger
Aleutian
Low
Higher pressure
Normal Atlantic jet
stream
Lower pressure
AO-related Pacific and Atlantic jet
stream
•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
Arctic Oscillation (AO): U.S. Winter Impacts
Positive AO
Stronger
Winds,
Waves
More
rain,
clouds
More Ice,
snow
Less rain
And clouds
Frequent warm-ups
Warmer
Fewer
Nor’easters
More heavy
rain events
Negative AO
Colder
More Nor’easters
More cold-air
outbreaks
Increased Snowfall
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
Map depicts warm
phase of AMO
˚C
•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.
The Atlantic Multi-Decadal Oscillation (AMO) and
Monsoon Rainfall in India and Western Africa
Observed AMO Index
Jun.-Sep. West Central India Rainfall Departures
Jun.-Sep. African Sahel Rainfall Departures
This AMO-Related Pattern Increases Atlantic Hurricane
Activity for Decades at a time
Warmer
Warmer
Wet
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)
Sea Surface Temperature Departures (Shading)
Negative Phase
Positive Phase
Can Reinforce El Niño
Can Reinforce La Niña
Observed PDO Index
•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
Summary
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).
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.
Combining these climate signals is very important for making seasonal
predictions.
Questions?