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

1. TeleconnectionsByDr. Gerry BellClimate 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 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.

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 Streams Jet Stream Wet Jet Streams produce a 4-celled pattern of wet/dry Winds flow clockwise around areas of High Pressure Winds flow counter-clockwise around areas of Low Pressure Dry Wet Storms Decay Here Storms Form Here L H Jet Core Jet Stream Jet Core Dry 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 H L L H L H 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.

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 NormalComparing Positive and Negative Phase Negative Phase Positive Phase Higher pressure Lower pressure Storm Formation region Winds • Stronger high / low pressure systems • Jet stream and region of storm formation shift eastward • Weaker high / low pressure systems • Jet stream and region of storm formation shifts west toward central Pacific.

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 L COLD H H Negative phase of PNA pattern favors blocking and strong cold-air outbreaks into western North America.

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 NormalComparing Positive and Negative Phase Positive Phase Negative Phase Higher pressure Lower pressure Storm Formation region Winds • Stronger high / low pressure systems • Jet stream and region of storm formation shift north and east • Weaker high / low pressure systems • Jet stream and region of storm formation shift to southern Europe

18. Winter NAO Index 50 55 60 65 70 75 80 85 90 95 00 03 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 H L Negative phase of NAO pattern favors blocking and strong cold-air outbreaks into northern Europe.

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 L L L L Stronger Aleutian Low Weaker Icelandic Low 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 Negative AO More Ice Inland snow 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 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

28. 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). Normal Ocean Surface Temperatures (°C)January

29. SST(°C) and Departures 28 28

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) 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 Jul Nov Jan Feb Jun Oct Sep Apr Mar Aug May

32. Niño 3.4 SST Forecasts (oC) 2 1.5 1 0.5 0 -0.5 -1 JJA MJJ AMJ DJF NDJ JFM FMA OND MAM 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. Strong La Nina Jet Stream Drier Wetter 4 8 12 16 20 • Tropical convection and • jet stream confined to western Pacific. • Triggers negative PNA pattern Wintertime Tropical Rainfall (Inches) Strong El Nino Jet Stream Drier Wetter 4 8 12 16 20 • 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. January-March Typical Conditions La Niña Polar jet stream • La Niña: • Pacific jet stream, storm track are variable • Periods with strong polar jet stream • More arctic outbreaks Cooler Warmer Drier Pacific jet stream, storm track more variable 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

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 Increased Wind Shear, Fewer Hurricanes Increased Wind Shear, Fewer Hurricanes More Shear Less Shear Warm, Wet Cool, Dry La Niña decreases the westerly winds over the Atlantic, reducing wind shear and enhancing hurricane activity. El Niño increases the westerly winds, over the Atlantic, increasing the wind shear and suppressing hurricane activity. La Niña El Niño 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 SignalCurrent High Activity Era Warmer Warmer Wet Drier 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 La Nina Low Activity Decades High Activity Decades Above Near Below Normal Normal Normal 6 0 1 Above Near Below Normal Normal Normal 1 2 2 El Nino Low Activity Decades High Activity Decades Above Near Below Normal Normal Normal 3 4 2 Above Near Below Normal Normal Normal 0 2 7

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