Teleconnections & The Teleconnections & The Zonal IndexZonal Index

Part I: The Big PicturePart I: The Big Picture

Brian Griffith & Jason FurtadoBrian Griffith & Jason FurtadoAT750 – Climate VariabilityAT750 – Climate Variability

Lecture 1Lecture 1

Quick OutlineQuick Outline► Teleconnection WorksTeleconnection Works

Walker and Bliss (1932)Walker and Bliss (1932) Pacific-North American PatternPacific-North American Pattern

► The Zonal Index Cycle & Atmospheric The Zonal Index Cycle & Atmospheric CirculationCirculation Rossby & Willett (1948)Rossby & Willett (1948)

► Zonally Symmetric SeesawZonally Symmetric Seesaw Lorenz (1951)Lorenz (1951)

► Onto Wallace & Gutzler (1981) and Wallace Onto Wallace & Gutzler (1981) and Wallace & Hsu (1985)& Hsu (1985)

The MotivationThe Motivation►What prompted scientists of the early What prompted scientists of the early

2020thth century to focus on finding century to focus on finding teleconnection and circulation teleconnection and circulation patterns?patterns? Understand the overall general circulation Understand the overall general circulation

of the planet.of the planet. Expand the predictability of future Expand the predictability of future

anomalies and weather patterns (extend anomalies and weather patterns (extend long range forecasts).long range forecasts).

Gain more insight into the dynamical Gain more insight into the dynamical principles of the atmosphere.principles of the atmosphere.

Some Key DefinitionsSome Key Definitions►Teleconnection: Teleconnection: A relationship A relationship

between changes in variables between between changes in variables between two locations two locations

►Zonal Index: Zonal Index: A measure of the A measure of the strength of the mid-latitude westerlies.strength of the mid-latitude westerlies.

►Zonal Symmetry: Zonal Symmetry: Equally distributed Equally distributed signal at all longitudes along a signal at all longitudes along a latitudinal belt.latitudinal belt. In this discussion, we look at zonally In this discussion, we look at zonally

symmetric symmetric see-sawssee-saws, which means anti-, which means anti-correlations between two latitudinal correlations between two latitudinal belts.belts.

Early Teleconnection WorkEarly Teleconnection Work► Walker & Bliss (1932) Walker & Bliss (1932)

investigated three (3) investigated three (3) “connected relationships” in “connected relationships” in the world’s circulation.the world’s circulation. North Atlantic Oscillation North Atlantic Oscillation

(NAO)(NAO) North Pacific Oscillation (NPO)North Pacific Oscillation (NPO) Southern Oscillation (SO)Southern Oscillation (SO)

► Used correlation coefficients Used correlation coefficients in T, P, and rainfall in T, P, and rainfall measurements between measurements between certain stations to define certain stations to define each pattern each pattern mathematicallymathematically

The NAOThe NAO

NAO+ NAO-Figure from J. M. Wallace, U. of Washington

More On The NAOMore On The NAO►Walker and Bliss (1932) defined the NAO Walker and Bliss (1932) defined the NAO

Index as:Index as:

►OK, but what does it fundamentally reflect?OK, but what does it fundamentally reflect? Changes in SLP between the Icelandic Low and Changes in SLP between the Icelandic Low and

Azorean HighAzorean High Affects temperatures in North America and Affects temperatures in North America and

Europe, as seen by van Loon and Rogers (1978)Europe, as seen by van Loon and Rogers (1978)

)(35.7.

7.

HatterasDCGodthaabIvigtut

mStykkisholBermudaStornowayBodoVienna

TTTP

PPTTP

The NPOThe NPO► The NPO has negatively correlated centers of action The NPO has negatively correlated centers of action

between Hawaii and an extended region from Siberia to between Hawaii and an extended region from Siberia to the Canadian Rockies (Walker and Bliss 1932).the Canadian Rockies (Walker and Bliss 1932).

► Originated from observations of storm tracks based on Originated from observations of storm tracks based on pressure in Alaska and the Intermountain West of the US. pressure in Alaska and the Intermountain West of the US.

From Walker and Bliss (1932)

The Pacific-North American The Pacific-North American PatternPattern

From Pacific Marine Environmental Lab http://www.pmel.noaa.gov/~miletta/images/pna.gif

Aleutian LowHawaii

“High Plateau” High

Gulf Coast

*Note: Wave-train signal in the PNA Pattern.Often recognized by SST changes in the Pacific.

Another center?

A Circulatory ArgumentA Circulatory Argument► Walker and Bliss’s Walker and Bliss’s

discussion depended solely discussion depended solely on surface measured on surface measured variables. (Why?)variables. (Why?)

► Enter the MIT Extended Enter the MIT Extended Forecasting Project (MIT Forecasting Project (MIT EFP) in the early 40s.EFP) in the early 40s. The ultimate goal – Make The ultimate goal – Make

longer, more accurate long longer, more accurate long range forecasts (several days range forecasts (several days to two weeks)to two weeks)

► But how can one hope to But how can one hope to make longer range forecasts make longer range forecasts without understanding a without understanding a simple simple general circulationgeneral circulation of the planet?of the planet?

► One theory – Hadley’s 1735 One theory – Hadley’s 1735 theory of the thermal theory of the thermal circulation that produces the circulation that produces the tropical trade winds.tropical trade winds. From Ahrens (1994)

Toward A Zonal TheoryToward A Zonal Theory► Rossby & Willett (1948) Rossby & Willett (1948)

investigated upper investigated upper troposphere / lower troposphere / lower stratosphere circulationstratosphere circulation

► They noticed that the They noticed that the polar jet stream had a polar jet stream had a tendency to oscillate tendency to oscillate between 35 and 55 N.between 35 and 55 N.

► This oscillation This oscillation coincided with coincided with expansion and expansion and contractions of the contractions of the polar vortex.polar vortex.

► In particular, Rossby & In particular, Rossby & Willett noticed that a 3-Willett noticed that a 3-8 week period 8 week period accompanied these jet accompanied these jet stream and polar stream and polar vortex changes.vortex changes.

Mean zonal Vg Jan. – Feb. (Rossby & Willett 1948)

Mean zonal Vg July-Aug. (Rossby & Willett 1948)

The Zonal Index CycleThe Zonal Index Cycle► With these observations, Rossby & Willett With these observations, Rossby & Willett

(1948) defined the (1948) defined the zonal index cyclezonal index cycle.. High Index: High Index: Stronger zonal flow in the higher Stronger zonal flow in the higher

latitudes, decreasing storminess and latitudes, decreasing storminess and meriodional air mass advection,meriodional air mass advection,

Low Index: Low Index: A weaker polar vortex, allowing A weaker polar vortex, allowing the jet stream to shift further south, allowing the jet stream to shift further south, allowing for a period of increased storminess.for a period of increased storminess.

► Rossby (1948) theorized that zonal index Rossby (1948) theorized that zonal index cycle changes could be predicted at cycle changes could be predicted at natural intervals based on radiational natural intervals based on radiational cooling effects at higher latitudes.cooling effects at higher latitudes. More importantly, Rossby (1948) formulated a More importantly, Rossby (1948) formulated a

realistic circulation model of the atmosphere.realistic circulation model of the atmosphere.

Rossby’s Circulation ModelRossby’s Circulation Model

Hadley Cell

Ferrell CellPolar Cell (?)

?

Nothing?

From Rossby and Willett (1948)

*Note: This entire circulation model was derived based on the zonal index cycle.According to Rossby (1948), fluctuations in the polar vortex strength and size causedthe movements of the jet streams and hence develop these cells.

Lorenz’s SeesawLorenz’s Seesaw► Lorenz (1951) Lorenz (1951)

investigated variations investigated variations in NH SLP data, seasonal in NH SLP data, seasonal and anomalous.and anomalous.

► Findings summarized on Findings summarized on the right – Lorenz found the right – Lorenz found two (2) zones in NH SLP.two (2) zones in NH SLP. ++rr within the zone, and within the zone, and

––rr with the other zone. with the other zone.► The connection: Lorenz The connection: Lorenz

linked the zones to the linked the zones to the fluctuations in the index fluctuations in the index cyclecycle

(top) NH mean SLP profiles connected withthe index cycles and (bottom) normal SLPprofiles for each month From Lorenz (1951).

Zonally Symmetric SeesawZonally Symmetric Seesaw

What Do We Have?What Do We Have?► Three (3) “relationship” (teleconnection) Three (3) “relationship” (teleconnection)

patternspatterns The NAO – SLP differences between points in the The NAO – SLP differences between points in the

Atlantic basis.Atlantic basis. The NPO – SLP differences between subtropical The NPO – SLP differences between subtropical

Pacific and Siberian-Alaskan-Rockies pressure Pacific and Siberian-Alaskan-Rockies pressure system.system.

The PNA – Wave train pattern in the central and The PNA – Wave train pattern in the central and eastern Pacific extending into N. Americaeastern Pacific extending into N. America

► The Zonal Index CycleThe Zonal Index Cycle Linked to expansions and contractions of the polar Linked to expansions and contractions of the polar

vortexvortex► The Zonally Symmetric SeesawThe Zonally Symmetric Seesaw

Mass transport between middle and higher latitudesMass transport between middle and higher latitudes Linked to zonal index changes.Linked to zonal index changes.

An Emerging InterestAn Emerging Interest► Teleconnection interests waned after the Teleconnection interests waned after the

early ’50s but picked up significantly in the early ’50s but picked up significantly in the late ’60s and early ’70s.late ’60s and early ’70s.

► Why a renewed interest in teleconnection Why a renewed interest in teleconnection patterns?patterns? Early ’60s into the ’70s - anomalously snowy & Early ’60s into the ’70s - anomalously snowy &

cold winters plagued the Eastern US as well as cold winters plagued the Eastern US as well as parts of W. Europe (Hurrell and van Loon 1997).parts of W. Europe (Hurrell and van Loon 1997).

► Linked to a long-lasting negative phase of the NAO.Linked to a long-lasting negative phase of the NAO. Dynamics of the proposed patterns not Dynamics of the proposed patterns not

understood or only speculated.understood or only speculated.► Forcing? Changes in ocean circulations?Forcing? Changes in ocean circulations?► Ocean-atmosphere coupling?Ocean-atmosphere coupling?

From Theory to More Objective From Theory to More Objective AnalysesAnalyses

► The earlier works were The earlier works were instrumental in laying instrumental in laying the foundations of the the foundations of the existence of these existence of these patterns, but much of the patterns, but much of the work was “subjective.”work was “subjective.”

► Later works by Kutzbach Later works by Kutzbach (1970), van Loon & (1970), van Loon & Rogers (1978) & Wallace Rogers (1978) & Wallace & Gutzler (1981) & Gutzler (1981) attempted to use attempted to use contemporary methods contemporary methods and data to recreate or and data to recreate or disprove the proposed disprove the proposed theories.theories. First EOF of January SLP from 1899 – 1969

(Kutzbach 1970).

More On Teleconnection More On Teleconnection WorkWork

There is a robust negative correlationbetween temperatures in Greenland &Oslo. (van Loon and Rogers 1978)

Correlations between IL mean positionSLP and all other points on the globe.Notice the north-south dipole in theAtlantic as well as the strong negativecorrelation in the Aleutians. (van Loonand Rogers 1978)

c

A Look AheadA Look Ahead►Wallace and Gutzler Wallace and Gutzler (1981)(1981)

One-point correlationOne-point correlation maps to identify maps to identify the individual patterns and then centers the individual patterns and then centers of action of each pattern.of action of each pattern.

CompositeComposite maps to understand maps to understand oscillations in planetary wave action.oscillations in planetary wave action.

►Wallace and HsuWallace and Hsu (1985) (1985) Eddy componentEddy component maps vs. composite maps vs. composite

maps of the zonal indexmaps of the zonal index►How How shouldshould they compare they compare ifif the zonal index the zonal index

cycle theory were true?cycle theory were true?

Part IIPart IIAnalyses of PapersAnalyses of Papers

Objective AnalysisObjective Analysis►Consider teleconnections emerging Consider teleconnections emerging

from objective treatment of datafrom objective treatment of data►Monthly mean SLP and 500mb GPH for Monthly mean SLP and 500mb GPH for

15 winter data set15 winter data set►Test reproducibility with independent Test reproducibility with independent

13 winter data set13 winter data set

Analysis TechniquesAnalysis Techniques►Apriori: one-point correlation mapsApriori: one-point correlation maps►Objective: eigenvector analysisObjective: eigenvector analysis

Fig 7Fig 7

SLP TeleconnectionsSLP Teleconnections►NAO: Teleconnection between NAO: Teleconnection between

(65N,20W) and (30N,20W)(65N,20W) and (30N,20W)►NPO: Teleconnection between NPO: Teleconnection between

(65N,170E) and (25N,165E)(65N,170E) and (25N,165E)

Fig 8Fig 8

Fig 10Fig 10

Fig 11Fig 11

500mb Teleconnections500mb Teleconnections►EA pattern: (25N,25W), (55N,20W), EA pattern: (25N,25W), (55N,20W),

(50N,40E)(50N,40E)►EA Index: positive indicatesEA Index: positive indicates

Fig 12Fig 12

Fig 13Fig 13

Fig 14Fig 14

Pacific/North AmericanPacific/North American►(20N,160W),(45N,165W),(55N,115W),(20N,160W),(45N,165W),(55N,115W),

(30N,85W)(30N,85W)►PNA index: positive with strong ridges PNA index: positive with strong ridges

over Canada, deep Aleutian low; over Canada, deep Aleutian low; negative associated w/ more zonal negative associated w/ more zonal 500mb GPH field500mb GPH field

Fig 16Fig 16

Fig 17Fig 17

Fig 18Fig 18

Western Atlantic PatternWestern Atlantic Pattern►(55N,55W),(30N,55W)(55N,55W),(30N,55W)►WA index: positive with weak jet over WA index: positive with weak jet over

western Atlantic, weak Icelandic low, western Atlantic, weak Icelandic low, weak subtropical high in SLP fieldweak subtropical high in SLP field

Fig 20Fig 20

Fig 21Fig 21

Fig 22Fig 22

Western Pacific PatternWestern Pacific Pattern►(60N,155E), (30N,155E)(60N,155E), (30N,155E)►WP index: positive with weak Aleutian WP index: positive with weak Aleutian

low, weak jet over Japanlow, weak jet over Japan

Fig 24Fig 24

Eurasian PatternEurasian Pattern►(55N,20E),(55N,75E),(40N,145E)(55N,20E),(55N,75E),(40N,145E)►EU index: positive EU with deep EU index: positive EU with deep

500mb GPH trough near 30E and 500mb GPH trough near 30E and strong Siberian sfc high; negative EU strong Siberian sfc high; negative EU has trough near 50Ehas trough near 50E

Fig 25Fig 25

Eigenvector AnalysisEigenvector Analysis►1st EV resembles WP pattern1st EV resembles WP pattern►2d EV resembles PNA pattern2d EV resembles PNA pattern►3d EV resembles EA pattern3d EV resembles EA pattern►4th EV resembles WA pattern4th EV resembles WA pattern►Differences btwn EV patterns and Differences btwn EV patterns and

teleconnections?teleconnections?

Fig 26Fig 26

Overlap of Patterns

Fig 27Fig 27

ReproducibilityReproducibility►13 independent winters13 independent winters►700mb instead of 500mb700mb instead of 500mb►1 point correlations demonstrate 1 point correlations demonstrate

similar patternssimilar patterns►EV patterns not as reproducibleEV patterns not as reproducible►Why?Why?

Fig 28aFig 28a

Fig 28eFig 28e

Fig 29Fig 29

Fig 30Fig 30

Zonal IndexZonal Index► Objectively examine relationship btwn ZI, Objectively examine relationship btwn ZI,

mean square eddy amplitude and standing mean square eddy amplitude and standing mode amplitudemode amplitude

► If ZI hypothesis true: should see strong If ZI hypothesis true: should see strong negative correlation btwn ZI and eddy negative correlation btwn ZI and eddy amplitude and composite high ZI maps amplitude and composite high ZI maps should resemble composite high eddy should resemble composite high eddy amplitude mapsamplitude maps

AnalysisAnalysis►ZI = avg SLP(35N) - avg SLP(55N)ZI = avg SLP(35N) - avg SLP(55N)►Eddy = average squared departure Eddy = average squared departure

from avg polar 500mb heightfrom avg polar 500mb height►Standing mode = normalized Standing mode = normalized

projection of transient eddy projection of transient eddy component of 500mb GPH on component of 500mb GPH on climatological meanclimatological mean

Fig1Fig1

Fig 3Fig 3

Fig 4Fig 4

Zonal Index?Zonal Index?► Fig 3 looks like Fig 4, not like Fig 1Fig 3 looks like Fig 4, not like Fig 1► Implies: Implies:

Variations in ZI not accompanied by major Variations in ZI not accompanied by major changes in eddy activitychanges in eddy activity

Variations in S account for much of observed Variations in S account for much of observed variability in eddy activityvariability in eddy activity

► Correlation btwn e and S = 0.64Correlation btwn e and S = 0.64► Correlation btwn e and ZI = -0.27Correlation btwn e and ZI = -0.27► Cross-spectrum analysis shows no Cross-spectrum analysis shows no

significant peaks btwn e and ZIsignificant peaks btwn e and ZI

Part IIIPart IIIConclusions & Final Conclusions & Final

RemarksRemarks

The Unanswered…The Unanswered…►Wallace and Gutzler (1981) ends with Wallace and Gutzler (1981) ends with

many many unanswered and unexplored issues. unanswered and unexplored issues. Connections with the Southern Hemisphere?Connections with the Southern Hemisphere?

►Symmetry!Symmetry! Extent of the teleconnection patterns?Extent of the teleconnection patterns?

►Upper troposphere? Stratosphere?Upper troposphere? Stratosphere? Are Are all all of these patterns realized exclusively?of these patterns realized exclusively?

►Which ones are “parent” patterns, and which are Which ones are “parent” patterns, and which are “children”?“children”?

Can the extratropics affect the tropics?Can the extratropics affect the tropics?

The Zonal Index Theory The Zonal Index Theory Falls…Falls…

► Wallace & Hsu (1985) Wallace & Hsu (1985) confirmed relocations confirmed relocations of mid-latitude of mid-latitude pressure systems pressure systems based on zonal wind based on zonal wind changes.changes. ButBut no zonally no zonally

symmetric T changes symmetric T changes and a lack of negative and a lack of negative correlation in the zonal correlation in the zonal index and eddy index and eddy component discredits component discredits Zonal Index TheoryZonal Index Theory

► What about the zonally What about the zonally symmetric see-saw?symmetric see-saw?

Composite difference (high – low) of1000 -500 mb thicknesses. The figure isproportional to mean temperature changes.(Wallace and Hsu 1985)

From Zonal to RegionalFrom Zonal to Regional► Essentially, Wallace and Hsu argue that “high Essentially, Wallace and Hsu argue that “high

index” and “low index” cycles may be more index” and “low index” cycles may be more regional.regional. E.g., NAO, PNA phase changesE.g., NAO, PNA phase changes Topographic/orographic features and patternsTopographic/orographic features and patterns

► The pair also looks at pressure gradients in The pair also looks at pressure gradients in different latitudinal belts (20-40 N and 45-65 N)different latitudinal belts (20-40 N and 45-65 N) Slight deterioration in signal in 20-40 NSlight deterioration in signal in 20-40 N 45-65 N have index differences in Atlantic sector and 45-65 N have index differences in Atlantic sector and

at high latitudesat high latitudes