1. Teleconnections By Dr. Gerry Bell Climate Prediction Center (CPC) NOAA/NWS/NCEP

2. 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

3. 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.

4. Monitoring Northern Hemisphere Teleconnections at CPC
Monitoring and Data
Index
Northern Hemisphere
Teleconnection Patterns
Monthly
Monthly Indices and time series, Calculation procedures, Descriptions of the ten leading patterns, Circulation maps, Temperature and precipitation departures.
Climate and Weather
AAO,AO,NAO,PNA
Daily
Daily indices, time series, model forecasts and forecast verifications of PNA, NAO, AO, AAO.

5. 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.

6. Air Pressure Patterns and Jet StreamsH
Winds flow clockwise around areas of High Pressure L
Winds flow counter-clockwise around areas of Low Pressure
Wet
Jet Core
Dry
Jet Stream
Jet Streams produce a 4-celled pattern of wet/dry
Jet Core
Jet Stream
Storms Form Here
Storms Decay Here
Jet streams strongly influence regions of storm formation

7. Setting the Stage: Average Winter Conditions
Air Pressure Pattern at Jet Stream Level (35,000 ft) L H L H
Main Regions Where Storms Form
East 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.

8. Some Northern Hemisphere Teleconnection Patterns
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.

9. Pacific/ North American Pattern (PNA)
The PNA is a main teleconnection pattern affecting the North Pacific and North America.

10. 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.

11. PNA Pattern Time Series: 3-Month Running Means
CPC index based on Rotated EOF analysis.

12. PNA: January Air Pressure Departures from Normal Comparing Positive and Negative Phase
Positive Phase
Negative Phase
Weaker high / low pressure systems
Jet stream and region of storm formation shifts west toward central Pacific.
Winds
Storm Formation region
Higher pressure
Lower pressure
Stronger high / low pressure systems
Jet stream and region of storm formation shift eastward

13. Pacific/ North American Pattern (PNA) Surface Temperature Correlations (x100)
PNA pattern influences N.A. surface temperatures mainly during cool-season.

14. 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.
COLD H H

15. Pacific/ North American Pattern (PNA) Precipitation Correlations (x100)
The PNA influence on precipitation varies during the year.

16. North Atlantic Oscillation (NAO)
The NAO is a main teleconnection pattern affecting eastern North America to Europe.

17. NAO: January Air Pressure Departures from Normal Comparing Positive and Negative Phase
Positive Phase
Weaker high / low pressure systems
Jet stream and region of storm formation shift to southern Europe
Negative Phase
Storm Formation region
Winds
Higher pressure
Lower pressure
Stronger high / low pressure systems
Jet stream and region of storm formation shift north and east

18. Winter NAO Index
Year
The NAO pattern can persist in one phase for decades at a time.

19. North Atlantic Oscillation (NAO) Surface Temperature Correlations

20. Surface Air Pressure Pattern Showing Blocking During Negative Phase of NAO
COLD
Negative phase of NAO pattern favors blocking and strong cold-air outbreaks into northern Europe. H L

21. North Atlantic Oscillation (NAO) Precipitation Correlations
The main precipitation signals for the NAO pattern are seen in Europe.

22. 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

23. Wintertime Arctic Oscillation (AO): Positive Phase
Maps show air pressure departures from normal.
Higher pressure
Lower pressure

24. Surface Air Pressure and Winds
Stronger Aleutian Low
Weaker Icelandic Low L L
Weaker Aleutian Low
Stronger Icelandic Low

25. Arctic Oscillation (AO): Significant Winter Impacts
Positive AO
Stronger Winds,
Waves
Frequent warm-ups
Fewer
Nor’easters
Warmer
More rain
And clouds
More heavy
rain events
More Ice
Inland snow
Negative AO
Colder
More Nor’easters
More cold-air outbreaks
Less rain
and clouds
Increased Snowfall

26. 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.

27. 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

28. 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
Warm pool in western Pacific and equatorial cold tongue in eastern Pacific.

29. SST(°C) and Departures28

30. 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

31. 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.
2009: Niño 3.4 Sea Surface Temperature Index (°C)
Jan
Mar
Feb
Apr
May
Jul
Jun
Aug
Sep
Oct
Nov -1
0.5 1
1.5
-0.5 2
-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

32. Niño 3.4 SST Forecasts (oC)-1
0.5 1
1.5
-0.5 2
OND
NDJ
DJF
JFM
FMA
MAM
AMJ
MJJ
JJA
Expected Peak Strength
Continue through Spring

33. 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.

34. Wintertime Tropical Rainfall (Inches)
Strong El Nino
Jet Stream
Wetter
Drier
Strong La Nina
Tropical convection and
jet stream confined to western Pacific.
Triggers negative PNA pattern
Jet Stream
Drier
Wetter
Tropical convection and
jet stream extend across central and eastern Pacific.
Triggers positive PNA pattern

35. Global El Niño Impacts December-February
El Niño impacts are strongest and most extensive in winter.
Some impacts are positive, some are negative

36. Wintertime Impacts in North America
January-March
Typical Conditions
Wintertime Impacts in North America
El Niño
El Niño:
Pacific jet stream, storm track are south of normal
Polar jet stream well into Canada
Fewer arctic outbreaks
Polar
jet stream
Warmer
Wetter
Pacific jet stream, storm track
Cooler
La Niña:
Pacific jet stream, storm track are variable
Periods with strong polar jet stream
More arctic outbreaks
Polar
jet stream
Cooler
Drier
Pacific jet stream, storm track more variable
La Niña
Warmer

37. CPC: Dec.-Feb. 2009-10 Seasonal Outlooks
Precipitation
Temperature
These outlooks largely reflect El Niño and long-term trends.

38. Combined Climate Impacts
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.

39. Winter El Niño – NAO Temperature Composites
El Niño Only
El Niño and Negative NAO
El Niño and Positive NAO oC

40. Influence on Atlantic Hurricane Activity
El Niño
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
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
Winds at 35,000 ft

41. Historical Atlantic Hurricane Season Strength
ACE index shows the overall strength of the hurricane season.
Multi-decadal fluctuations in season strength are clearly evident.

42. Tropical Multi-Decadal Signal Current High Activity Era
Drier
Warmer
Wet
High-activity eras are associated with the above climate conditions.
Low-activity eras have opposite departures from normal.

43. Conditions For Active Atlantic Hurricane Era

44. Atlantic Hurricane Activity
Above Near Below
Normal Normal Normal
El Nino
High Activity Decades
Low Activity Decades
Above Near Below
Normal Normal Normal
La Nina
High Activity Decades
Above Near Below
Low Activity Decades

45. 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.

46. H L Jet Stream Jet Stream Jet Core Jet Stream Jet Core Wet Dry
Jet Streams produce a 4-celled pattern of wet/dry
Jet Core
Jet Stream
Storms 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