teleconnections by dr. gerry bell climate prediction center (cpc) noaa/nws/ncep
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Teleconnections
By
Dr. Gerry BellClimate 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
Climate and Weather AAO,AO,NAO,PNADailyhttp://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.
Monitoring and Data Index
Northern HemisphereTeleconnection Patterns
Monthly
http://www.cpc.ncep.noaa.gov/data/teledoc/telecontents.shtmlMonthly Indices and time series, Calculation procedures, Descriptions of the ten leading patterns, Circulation maps, Temperature and precipitation departures.
Use Care with Teleconnection IndicesSeveral 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
Wet
Jet CoreDry
Dry
WetJet Stream
Jet Streams produce a 4-celled pattern of wet/dry
Jet CoreJet StreamStorms
Form Here
Storms Decay Here
H
Winds flow clockwise around areas of High Pressure
L
Winds flow counter-clockwise around areas of Low Pressure
Setting the Stage: Average Winter Conditions
L
L
H
H
L H
LH
Main Regions Where Storms FormEast Asian Jet Stream Atlantic Jet Stream
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.
Air Pressure Pattern at Jet Stream Level (35,000 ft)
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)
Maps also depict air pressure departures during positive phase of PNA pattern.
PNA pattern changes between winter and summer.
Higher pressure Lower pressure
January July
PNA Pattern Time Series: 3-Month Running Means
CPC index based on Rotated EOF analysis.
Negative Phase
•Weaker high / low pressure systems
•Jet stream and region of storm formation shifts west toward central Pacific.
PNA: January Air Pressure Departures from NormalComparing Positive and Negative Phase
Higher pressure Lower pressure
Winds Storm Formation region
•Stronger high / low pressure systems
•Jet stream and region of storm formation shift eastward
Positive Phase
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
Negative phase of PNA pattern favors blocking and strong cold-air outbreaks into western North America.
COLDLH
H
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.
•Weaker high / low pressure systems
•Jet stream and region of storm formation shift to southern Europe
Negative Phase
NAO: January Air Pressure Departures from NormalComparing Positive and Negative Phase
Higher pressure Lower pressure
Storm Formation region
•Stronger high / low pressure systems
•Jet stream and region of storm formation shift north and east
Positive Phase
Winds
Winter NAO Index
Year 50 55 60 65 70 75 80 85 90 95 00 03
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
LH COLD
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
Higher pressure Lower pressure
Maps show air pressure departures from normal.
Surface Air Pressure and Winds
Weaker Aleutian Low Stronger Icelandic Low
LL
Stronger Aleutian Low Weaker Icelandic Low
L L
Arctic Oscillation (AO): Significant Winter Impacts
Positive AO
Negative AO
Warmer
Colder
FewerNor’easters
More Nor’eastersMore cold-air outbreaks
Increased Snowfall
More heavy rain events
Frequent warm-ups
More IceInland snow
Less rainand clouds
More rainAnd clouds
Stronger Winds,Waves
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.
Climate & Weather
El Niño /La Nina
Monitoring El Niño and La Niña (ENSO)
•Current Conditions—Weekly Update (.ppt)•Animations•Weekly and Monthly Analyses•Indices•Diagnostics Discussion•Tutorial
ENSO Diagnostics Discussion
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml
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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.
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).
Warm, Wet
Cool, Dry
SST(°C) and Departures
28 28
El Niño is present. Expected to strengthen and last into the spring. A moderate strength event is most likely.
ENSO Alert System Status: El Nino Advisory
Niño 3.4 Region
Temperature Departures (oC): Last 30 Days
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.
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
2009: Niño 3.4 Sea Surface Temperature Index (°C) Ja
n
MarFeb
Apr
May Ju
l
Jun
Aug
Sep
Oct
Nov
The current El Niño developed in June
Niño 3.4 SST Forecasts (oC)
-1
0
0.5
1
1.5
-0.5
2
ON
D
ND
J
DJF
JFM
FMA
MAM AM
J
MJJ
JJA
Expected Peak Strength
Continue through Spring
El Niño and La Niña: 1950-PresentClassified 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.
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Wintertime Tropical Rainfall (Inches)
•Tropical convection and jet stream extend across central and eastern Pacific.
•Triggers positive PNA pattern
Jet Stream
WetterDrier
Strong El Nino
4 8 12 16 20
Jet Stream
Wetter Drier
Strong La Nina
•Tropical convection and jet stream confined to western Pacific.
•Triggers negative PNA pattern
4 8 12 16 20
35
Global El Niño Impacts
•El Niño impacts are strongest and most extensive in winter.
•Some impacts are positive, some are negative
December-February
36
El Niño:•Pacific jet stream, storm track are south of normal•Polar jet stream well into Canada•Fewer arctic outbreaks
January-MarchTypical ConditionsWintertime Impacts in North America
Pacific jet stream, storm track
Polar jet streamWarmer
Wetter
El Niño
Cooler
La Niña:•Pacific jet stream, storm track are variable •Periods with strong polar jet stream•More arctic outbreaks
Polar jet stream Cooler
DrierPacific jet stream, storm track more variable
La Niña
Warmer
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.
El Niño and Negative NAO
El Niño Only
oC
Winter El Niño – NAO Temperature Composites
El Niño and Positive NAO
40
Influence on Atlantic Hurricane Activity
El Niño increases the westerly winds, over the Atlantic, increasing the wind shear and suppressing hurricane activity.
More Shear
Increased Wind Shear, Fewer Hurricanes
Warm, Wet
El Niño
Winds at 35,000 ft
La Niña decreases the westerly winds over the Atlantic, reducing wind shear and enhancing hurricane activity.
Less Shear
Increased Wind Shear, Fewer Hurricanes
Cool, Dry
La Niña
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 SignalCurrent High Activity Era
DrierDrier
WarmerWetWet
Warmer
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
Above Near BelowNormal Normal Normal 3 4 2
El NinoHigh Activity Decades
Above Near BelowNormal Normal Normal 0 2 7
Low Activity Decades
Above Near BelowNormal Normal Normal 6 0 1
La Nina
High Activity Decades Above Near BelowNormal Normal Normal 1 2 2
Low Activity Decades
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
Wet
Jet CoreDry
Dry
WetJet Stream
Jet Streams produce a 4-celled pattern of wet/dry
Jet CoreJet StreamStorms
Form Here
Storms Decay Here
Jet streams strongly influence regions of storm formation
H
Winds flow clockwise around areas of High Pressure
L
Winds flow counter-clockwise around areas of Low Pressure
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