Teleconnections By Dr Gerry Bell Climate Prediction Center

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, 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, 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 Dry Wet L Jet. Stream Core Jet Wet Dry Jet Streams produce a 4 -celled pattern of wet/dry Storms Decay Here Storms Jet. Stream 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 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 (x 100) January July Higher pressure Lower pressure Maps also depict air pressure departures during positive phase of 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 (x 100) 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 COLD L H Negative phase of PNA pattern favors blocking and strong cold-air outbreaks into western North America.

Pacific/ North American Pattern (PNA) Precipitation Correlations (x 100) 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

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.

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 (o. C): 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 Jan 2009: Niño 3. 4 Sea Surface Temperature Index (°C) 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 (o. C) 2 1. 5 1 0. 5 0 -0. 5 JJA MJJ AMJ FMA MAM Expected Peak Strength JFM DJF NDJ OND -1 Continue through Spring

El Niño and La Niña: 1950 -Present Classified using Oceanic Niño Index (ONI, o. C): 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. 9 o. C.

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 Wa rme r Wetter Pacific jet stream, storm track La Niña Polar jet stream Pacific jet stream, storm track more variable El Niño: • Pacific jet stream, storm track are south of normal • Polar jet stream well into Canada • Fewer arctic outbreaks Co Cooler ole r La Niña: • Pacific jet stream, storm track are variable • Periods with strong polar jet stream • More arctic outbreaks Drier Warmer 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 o. C

Influence on Atlantic Hurricane Activity El Niño La Niña 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 Wet Drie r 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 Low Activity Decades Above Near Below Normal 3 4 2 Above Near Below Normal 0 2 7 La Nina High Activity Decades Above Near Below Normal 6 0 1 Low Activity Decades Above Near Below 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 Jet. Stream Core Jet Wet Dry Jet Streams produce a 4 -celled pattern of wet/dry Storms Decay Here Storms Jet. Stream Core Form Here 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