Download Teleconnections By Dr. Gerry Bell Climate Prediction Center (CPC)

Teleconnections
By
Dr. Gerry Bell
Climate Prediction Center (CPC)
NOAA/NWS/NCEP
Outline
•General concepts
•Teleconnection Patterns: What they are
• CPC Monitoring
•Use care with teleconnection indices
•Setting the stage: Average winter conditions
•Some Northern Hemisphere teleconnection patterns
•Pacific/ North American Pattern (PNA)
•North Atlantic Oscillation (NAO)
•Arctic Oscillation (AO)
•Tropical teleconnections
•El Niño and La Niña
•Tropical Multi-decadal Signal
•Summary
Teleconnection Patterns: What They Are
Definition:
Recurring and persistent, air pressure and circulation patterns
spanning vast geographical areas. Also called “leading modes of
variability, “ or “circulation regimes.”
Impacts:
•
•
Anomalous weather over seemingly vast distances: entire ocean
basins, continents, some are global.
Strong seasonality.
Monitoring Northern Hemisphere
Teleconnections at CPC
Monthly Monitoring and Data
Index
Northern Hemisphere
Teleconnection Patterns
http://www.cpc.ncep.noaa.gov/data/teledoc/telecontents.shtml
Monthly Indices and time series, Calculation procedures,
Descriptions of the ten leading patterns, Circulation maps,
Temperature and precipitation departures.
Daily
Climate and Weather
AAO,AO,NAO,PNA
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao
_index/teleconnections.shtml
Daily indices, time series, model forecasts and forecast
verifications of PNA, NAO, AO, AAO.
Use Care with Teleconnection Indices
Several different indices are often available, with differing calculation
procedures (grid point, area averaging, rotated EOF or RPCA).
Problems with indices based on grid points or area averaging:
•Don’t recognize that patterns and strengths vary seasonally (e.g. Winter
PNA index used to assess summer conditions).
•Independently calculated for each teleconnection pattern (PNA, NAO).
•Some patterns overlap spatially.
•Techniques cannot isolate pattern for which anomalies belong.
•Same pressure anomaly can be reflected in several different indices
CPC’s indices are based on rotated EOF analysis (Barnston and Livezey 1987):
•Above problems avoided.
•Indices for all patterns are computed simultaneously.
•Indices reflect the combination of patterns/ strengths that best explain
the observed monthly (or daily) anomaly pattern.
Air Pressure Patterns and Jet Streams
Winds flow clockwise around
areas of High Pressure
Winds flow counter-clockwise
around areas of Low Pressure
H
L
Dry
Wet
JetStream
Core
Jet
Wet
Dry
Jet Streams produce a 4-celled pattern of wet/dry
Storms
Decay
Here
Storms
JetStream
Core Form Here
Jet
Setting the Stage: Average Winter Conditions
Air Pressure Pattern at Jet Stream Level (35,000 ft)
L
H
H
L
H
L
H
L
Atlantic Jet Stream
East Asian Jet Stream
Main Regions Where Storms Form
High pressure (H) and low pressure (L) areas, and jet streams strongly
influence regions of storm formation, precipitation and temperature.
These patterns vary substantially. Preferred patterns are called
teleconnections.
Some Northern Hemisphere
Teleconnection Patterns
1. Pacific/ North American Pattern (PNA)
•
A main teleconnection pattern affecting the North Pacific
and North America.
2. North Atlantic Oscillation (NAO)
•
A main teleconnection pattern affecting eastern North
America to Europe.
PNA and NAO are continental scale wind/ pressure patterns
linked to recurring jet stream patterns.
3. Arctic Oscillation (AO)
Hemispheric pattern linked to polar-mid latitude mass
exchanges– Features aspects of PNA and NAO patterns.
Pacific/ North American Pattern (PNA)
The PNA is a main teleconnection pattern affecting the
North Pacific and North America.
PNA Teleconnection Pattern
Air Pressure Correlations (x100)
January
July
Higher pressure
Lower pressure
Maps also depict air pressure departures during
positive phase of PNA pattern.
PNA pattern changes between winter and summer.
PNA Pattern Time Series: 3-Month Running Means
CPC index based on Rotated EOF analysis.
PNA: January Air Pressure Departures from Normal
Comparing Positive and Negative Phase
Positive Phase
Negative Phase
Higher pressure
Lower pressure
Winds
Storm Formation region
•Stronger high / low pressure systems
•Weaker high / low pressure systems
•Jet stream and region of storm
formation shift eastward
•Jet stream and region of storm
formation shifts west toward central
Pacific.
Pacific/ North American Pattern (PNA)
Surface Temperature Correlations (x100)
PNA pattern influences N.A. surface temperatures mainly during cool-season.
Surface Air Pressure and Jet Stream Showing
Blocking During Negative Phase of PNA Pattern
H
L
COLD
H
Negative phase of PNA pattern favors blocking and strong cold-air outbreaks
into western North America.
Pacific/ North American Pattern (PNA)
Precipitation Correlations (x100)
The PNA influence on precipitation varies during the year.
North Atlantic Oscillation (NAO)
The NAO is a main teleconnection pattern affecting
eastern North America to Europe.
NAO: January Air Pressure Departures from Normal
Comparing Positive and Negative Phase
Positive Phase
Higher pressure
Winds
Negative Phase
Lower pressure
Storm Formation region
•Stronger high / low pressure systems
•Weaker high / low pressure systems
•Jet stream and region of storm
formation shift north and east
•Jet stream and region of storm
formation shift to southern Europe
DJF Seasonal NAO Index
Winter NAO Index
Standardized Amplitude
3
2
1
0
-1
-2
-3
50
55
60
65
70
75
80 85 90
95 00 03
Year
Year
The NAO pattern can persist in one phase for decades at a time.
North Atlantic Oscillation (NAO)
Surface Temperature Correlations
Surface Air Pressure Pattern Showing
Blocking During Negative Phase of NAO
H
COLD
L
Negative phase of NAO pattern favors blocking and strong cold-air outbreaks
into northern Europe.
North Atlantic Oscillation (NAO)
Precipitation Correlations
The main precipitation signals for the NAO pattern are seen in Europe.
Arctic Oscillation (AO)
•AO reflects mass exchange between polar region and middle latitudes
•Affects Pacific and North Atlantic storm tracks, jets
•Features aspects of PNA and NAO pattern
Wintertime Arctic Oscillation (AO): Positive Phase
Maps show air pressure departures from normal.
Higher pressure
Lower pressure
Surface Air Pressure and Winds
L
L
Weaker Aleutian Low
Stronger Icelandic Low
L
L
Stronger Aleutian Low
Weaker Icelandic Low
Arctic Oscillation (AO): Significant Winter Impacts
Positive AO
Stronger Winds,
Waves
More rain
And clouds
Frequent warm-ups
Warmer
Fewer
Nor’easters
More heavy
rain events
More Ice
Inland snow
Less rain
and clouds
Negative AO
Colder
More Nor’easters
More cold-air outbreaks
Increased Snowfall
El Niño and La Niña
•El Niño and La Niña are naturally occurring climate phenomena, and
represent extremes in the El Niño/ Southern Oscillation (ENSO).
•El Niño: a periodic warming (every 3-6 years) of the central and
eastern equatorial Pacific .
•La Niña: a periodic cooling (every 3-6 years) of the central and
eastern equatorial Pacific.
Monitoring El Niño and La Niña (ENSO)
Climate &
Weather
El Niño /La Nina
ENSO Diagnostics
Discussion
•Current Conditions—Weekly Update (.ppt)
•Animations
•Weekly and Monthly Analyses
•Indices
•Diagnostics Discussion
•Tutorial
http://www.cpc.ncep.noaa.gov/products/analysis_monito
ring/enso_advisory/index.shtml
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/
MJO/enso.shtml
Normal Ocean Surface Temperatures (°C)
January
Warm, Wet
Equator
Cool, Dry
Date Line
Equatorial ocean temperatures are normally warmest in the
western Pacific and coolest in the eastern Pacific.
In the central and eastern Pacific, there is a lot of year-to-year
variability. Some years are much warmer and wetter (El Niño)
and some years are much cooler and drier (La Niña).
28
SST(°C) and Departures
28
28
ENSO Alert System Status: El Nino Advisory
El Niño is present. Expected to strengthen and last into the
spring. A moderate strength event is most likely.
Temperature Departures (oC): Last 30 Days
Niño 3.4
Region
Defining El Niño and La Niña
Real-time: El Niño or La Niña conditions are present when the monthly SST
departures in Niño 3.4 region meet or exceed +/- 0.5°C along with
consistent atmospheric features. Anomalies must be forecasted to persist
for 3 consecutive months.
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
2009: Niño 3.4 Sea Surface Temperature Index (°C)
Jan
2
1.5
1
0.5
0
-0.5
-1
-1.5
The current El Niño developed in June
Strength Thresholds:
Weak:
Monthly Niño 3.4 index is 0.5° to 1°C.
Moderate: Monthly Niño 3.4 index is 1.0° to 1.5°C.
Strong:
Monthly Niño 3.4 index exceeds 1.5°C
Niño 3.4 SST Forecasts (oC)
2
1.5
1
0.5
0
-0.5
Expected Peak
Strength
JJA
MJJ
AMJ
MAM
FMA
JFM
DJF
NDJ
OND
-1
Continue through
Spring
El Niño and La Niña: 1950-Present
Classified using Oceanic Niño Index (ONI, oC): Three-month
running-mean SST departures in the Niño 3.4 region.
Historical Classification:
El Niño: ONI ≥ +0.5°C
La Niña: ONI ≤ -0.5°C
Must persist for five
consecutive overlapping
3-month seasons.
Most recent ONI value
(August – October
2009) is +0.9oC.
Wintertime Tropical Rainfall (Inches)
Strong La Nina
Jet Stream
Strong El Nino
Jet Stream
Drier
4
Wetter
8
12
16
20
Wetter
Drier
4
12
8
16
20
•Tropical convection and
jet stream extend across
central and eastern Pacific.
•Tropical convection and
jet stream confined to western
Pacific.
•Triggers positive PNA pattern
•Triggers negative PNA pattern
34
Global El Niño Impacts
December-February
•El Niño impacts are strongest and most extensive in winter.
•Some impacts are positive, some are negative
35
Wintertime
January-March
Impacts
in North
Typical Conditions
America
El Niño
Polar
jet stream
Wetter
Pacific jet stream, storm track
La Niña
Polar
jet stream
El Niño:
•Pacific jet stream, storm
track are south of normal
•Polar jet stream well
into Canada
•Fewer arctic outbreaks
Cooler
La Niña:
•Pacific jet stream, storm
track are variable
•Periods with strong
polar jet stream
•More arctic outbreaks
Warmer
Pacific jet stream, storm
track more variable
36
CPC: Dec.-Feb. 2009-10 Seasonal Outlooks
Temperature
Precipitation
These outlooks largely reflect El Niño and long-term trends.
Combined Climate Impacts
1.
Understanding combinations of signals is key to
understanding observed climate variability and improving
seasonal predictions.
2. El Niño impacts can vary depending on
•
Other teleconnections: NAO, AO
•
Tropical rainfall and temperature patterns that can last
for decades: called multi-decadal signal– affects hurricanes
3. Care must be taken when performing regression analysis on
individual climate factors.
Winter El Niño – NAO Temperature Composites
El Niño Only
El Niño and
Negative NAO
El Niño and
Positive NAO
oC
Influence on Atlantic Hurricane Activity
El Niño
La Niña
Increased Wind Shear, Fewer Hurricanes
Increased Wind Shear, Fewer Hurricanes
Warm, Wet
More
Shear
Cool, Dry
Less
Shear
Winds at 35,000 ft
El Niño increases the westerly winds,
over the Atlantic, increasing the wind
shear and suppressing hurricane
activity.
40
La Niña decreases the westerly winds
over the Atlantic, reducing wind shear
and enhancing hurricane activity.
Historical Atlantic Hurricane Season Strength
ACE index shows the overall strength of the hurricane season.
Multi-decadal fluctuations in season strength are clearly evident.
Tropical Multi-Decadal Signal
Current High Activity Era
Warmer
Warmer
Wet
High-activity eras are associated with the above climate conditions.
Low-activity eras have opposite departures from normal.
Conditions For Active Atlantic Hurricane Era
Atlantic Hurricane Activity
El Nino
High Activity Decades
Above
Near
Below
Normal Normal Normal
3
4
2
Low Activity Decades
Above
Near
Below
Normal Normal Normal
0
2
7
La Nina
High Activity Decades
Above Near
Below
Normal Normal Normal
6
0
1
Low Activity Decades
Above
Near
Below
Normal Normal Normal
1
2
2
Summary
PNA and NAO Teleconnection Patterns:
• Seasonally dependent, continental scale, linked to recurring jet
stream patterns, Vary months to seasons to decades (NAO).
• EOF-based indices are better (CPC)
Arctic Oscillation (AO):
• Combines parts of PNA and NAO
• Hemispheric impacts linked to polar-mid latitude mass exchange.
Tropics
• El Niño/ La Niña:
• Niño 3.4 and ONI indices
• Global teleconnections, strongest in winter hemisphere
• El Niño is present and will last into the spring.
•
Multi-decadal signal: Atlantic SSTs and west African monsoon.
•
Combinations of climate signals for understanding observed climate
variability and improving seasonal predictions.
Jet Stream
Dry
Wet
JetStream
Core
Jet
Dry
Wet
Jet Streams produce a 4-celled pattern of wet/dry
Storms
Decay
Here
Storms
JetStream
Core Form Here
Jet
Jet streams strongly influence regions of storm formation
Winds flow clockwise around
areas of High Pressure
H
Winds flow counter-clockwise
around areas of Low Pressure
L