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Northern Hemispheric Northern Hemispheric Flow Indices Flow Indices Knight & Grumm Knight & Grumm NWS-PSU NWS-PSU 485 Lecture Series 485 Lecture Series

Northern Hemispheric Flow Indices

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Northern Hemispheric Flow Indices. Knight & Grumm NWS-PSU 485 Lecture Series. Annular Modes. A different view of the zonal index global sea level pressure at 55N/S Northern (NAM) and Southern (SAM) positive index: westerlies are strong negative index: more meridional flow - PowerPoint PPT Presentation

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Page 1: Northern Hemispheric Flow Indices

Northern Hemispheric Northern Hemispheric Flow IndicesFlow Indices

Knight & GrummKnight & Grumm

NWS-PSUNWS-PSU

485 Lecture Series485 Lecture Series

Page 2: Northern Hemispheric Flow Indices

Annular ModesAnnular Modes

A different view of the zonal indexA different view of the zonal index– global sea level pressure at 55N/Sglobal sea level pressure at 55N/S– Northern (NAM) and Southern (SAM)Northern (NAM) and Southern (SAM)– positive index: westerlies are strongpositive index: westerlies are strong– negative index: more meridional flownegative index: more meridional flow

averaged by day, week, month, seasonaveraged by day, week, month, season most significant in the winter (NH)most significant in the winter (NH)

Page 3: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

NAM averaged for NAM averaged for Jan-Feb-Mar (high) Jan-Feb-Mar (high)

NAM averaged for NAM averaged for Jan-Feb-Mar (low) Jan-Feb-Mar (low)

Page 4: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

NAM averaged NAM averaged Jan-Feb-Mar (high) Jan-Feb-Mar (high)

NAM averagedNAM averagedJan-Feb-Mar (low)Jan-Feb-Mar (low)

Page 5: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

Blue shading Blue shading indicates ratio of indicates ratio of

cold days (T<1.5sd)cold days (T<1.5sd)to low values ofto low values of

NAMNAM

Page 6: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

Page 7: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

The Polar Night Jet (PNJ) oscillates in The Polar Night Jet (PNJ) oscillates in the stratospherethe stratosphere– develops each autumn at about 20km develops each autumn at about 20km

and reaches speeds of 50m/sand reaches speeds of 50m/s– Northern Hemisphere PNJ is asymmetric Northern Hemisphere PNJ is asymmetric

due to thermal contrasts of land/oceansdue to thermal contrasts of land/oceans– PNJ is perturbed by upward propagating PNJ is perturbed by upward propagating

velocity waves (due to baroclinic waves)velocity waves (due to baroclinic waves)

Page 8: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

PNJ DissipationPNJ Dissipation– In Northern Hemisphere, deformation of the In Northern Hemisphere, deformation of the

polar vortex plus upward propagating polar vortex plus upward propagating planetary waves leads to rapid weakening of planetary waves leads to rapid weakening of the jet.the jet.

– lower polar stratosphere can warm by 50C as lower polar stratosphere can warm by 50C as upper stratospheric air replaces cold core jet. upper stratospheric air replaces cold core jet.

– Warmth can propagate to the surface at the Warmth can propagate to the surface at the high latitudes. (according to O’Lenic – January high latitudes. (according to O’Lenic – January 2004)2004)

Page 9: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

Stratosphere Stratosphere Temperatures - Feb 29 Temperatures - Feb 29 20042004

Page 10: Northern Hemispheric Flow Indices

Annular ModeAnnular Mode

Global Warming and the NAMGlobal Warming and the NAM– Many GCM predict warming in troposphere Many GCM predict warming in troposphere

and cooling in stratosphereand cooling in stratosphere– This causes a steep thermal gradient in This causes a steep thermal gradient in

the lower stratosphere due to tilted the lower stratosphere due to tilted tropopausetropopause

– In turn, leads to stronger than average PNJ In turn, leads to stronger than average PNJ which locks coldest air near the Polewhich locks coldest air near the Pole

– Explains warmth of most winters since Explains warmth of most winters since 1980’s and patches of frigid air in far north1980’s and patches of frigid air in far north

Page 11: Northern Hemispheric Flow Indices

Regional Flow IndicesRegional Flow Indices

Indices that affect the flow and Indices that affect the flow and climatology over North America and climatology over North America and EurasiaEurasia– North Atlantic Oscillation (NAO)North Atlantic Oscillation (NAO)– Pacific North American pattern (PNA)Pacific North American pattern (PNA)– Eastern Pacific Index (EP)Eastern Pacific Index (EP)

DefinitionsDefinitions Impacts on weather Impacts on weather ……and a bit of history…..and a bit of history…..

Page 12: Northern Hemispheric Flow Indices

North Atlantic OscillationNorth Atlantic Oscillation

A measure of the flow over the Atlantic BasinA measure of the flow over the Atlantic Basin Typically, the value is computed using MSLP Typically, the value is computed using MSLP

departuresdepartures– over Iceland and the Azoresover Iceland and the Azores– high or positive NAO associated with deep high or positive NAO associated with deep

Icelandic lowIcelandic low– low or negative NAO associated with ridge over low or negative NAO associated with ridge over

Iceland and NorwayIceland and Norway Periods of low NAO have been linked to cold Periods of low NAO have been linked to cold

times in Northern Europe and North Americatimes in Northern Europe and North America– the Little Ice Age ~1300-1860the Little Ice Age ~1300-1860

Page 13: Northern Hemispheric Flow Indices

North Atlantic OscillationNorth Atlantic Oscillation

Monthly and Seasonal, raw and normalized, Monthly and Seasonal, raw and normalized, indices of the NAO are based on the indices of the NAO are based on the difference in sea level pressure between difference in sea level pressure between Ponta Delgada, Azores (38°N, 26°W) and Ponta Delgada, Azores (38°N, 26°W) and Akureyri, Iceland (66°N, 18°W) from 1874-Akureyri, Iceland (66°N, 18°W) from 1874-2000. Raw indices are obtained as the 2000. Raw indices are obtained as the simple monthly sea level pressure anomaly simple monthly sea level pressure anomaly difference between the two stations, biased difference between the two stations, biased toward the Arctic where the standard toward the Arctic where the standard deviation in pressures is approximately deviation in pressures is approximately twice that of the subtropical Azores location twice that of the subtropical Azores location

Page 14: Northern Hemispheric Flow Indices

NAONAOhttp://www.cru.uea.ac.uk/tiempo/floor2/data/nao.htmNAOhttp://www.cru.uea.ac.uk/tiempo/floor2/data/nao.htmNAO

Strictly the index should only be applied in the Strictly the index should only be applied in the cold seasoncold season

Last period of low NAO: the winter of 1995-96Last period of low NAO: the winter of 1995-96 Historically:Historically:

– NAO did fluctuate more in the past than recent timesNAO did fluctuate more in the past than recent times– We know this from history:We know this from history:

wine harvest dates (later was a cold year)wine harvest dates (later was a cold year) wheat harvests and periods of European Faminewheat harvests and periods of European Famine

– wheat and other grains failed or produced bad crops in cold wet wheat and other grains failed or produced bad crops in cold wet years.years.

shipping and fishing industries back to Nordic andshipping and fishing industries back to Nordic and Basque Basque fishing times. fishing times.

– they followed the water-temperature sensitive Cod fishthey followed the water-temperature sensitive Cod fish

Page 15: Northern Hemispheric Flow Indices

NAO-Positive PhaseNAO-Positive Phase

A stronger than usual subtropical high pressure A stronger than usual subtropical high pressure center and a deeper than normal Icelandic lowcenter and a deeper than normal Icelandic low

The increased pressure difference results in more The increased pressure difference results in more numerous and stronger winter storms crossing the numerous and stronger winter storms crossing the Atlantic Ocean on a more northerly track.Atlantic Ocean on a more northerly track.– Wetter in western EuropeWetter in western Europe

– Keeps cold air out of EuropeKeeps cold air out of Europe

North American WeatherNorth American Weather– Cold and dry winters in northern Canada and GreenlandCold and dry winters in northern Canada and Greenland

– The eastern US experiences mild and wet winter conditionsThe eastern US experiences mild and wet winter conditions

Page 16: Northern Hemispheric Flow Indices

NAO-Positive PhaseNAO-Positive Phase

Page 17: Northern Hemispheric Flow Indices

NAO-Negative PhaseNAO-Negative Phase

Shows a weak subtropical high and a weak Icelandic Shows a weak subtropical high and a weak Icelandic low. low.

A reduced pressure gradient results in fewer and A reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east weaker winter storms crossing on a more west-east path. path. – Moist Atlantic air moves into the MediterraneanMoist Atlantic air moves into the Mediterranean

– Cold air to northern EuropeCold air to northern Europe

– Associated with many record cold European winters Associated with many record cold European winters

– US east coast experiences more cold air outbreaks and US east coast experiences more cold air outbreaks and snowy weather conditions. snowy weather conditions.

– Greenland, has milder winter temperaturesGreenland, has milder winter temperatures during the warm conditions 800-1250, negative NAOs during the warm conditions 800-1250, negative NAOs

may have allowed farming and fishing in Greenlandmay have allowed farming and fishing in Greenland

Page 18: Northern Hemispheric Flow Indices

NAO-Negative PhaseNAO-Negative Phase

Page 19: Northern Hemispheric Flow Indices

NAO in recent historyNAO in recent history

Page 20: Northern Hemispheric Flow Indices

NAO by Seasons

Page 21: Northern Hemispheric Flow Indices

Annual NAO ValuesAnnual NAO Values 00 01 02 03 04 05 06 07 08 09

1860 -0.66 -0.20 -3.04 4.14 0.421870 -2.77 -0.85 -0.83 0.17 2.32 -2.10 -1.85 -0.24 -4.03 -0.691880 -1.86 -2.84 2.06 1.73 1.38 -1.40 0.20 -3.05 -2.94 2.571890 2.97 -0.34 -2.49 -1.32 2.28 -3.41 1.58 0.38 0.95 -2.401900 0.22 -0.78 -2.61 1.69 1.46 1.12 2.29 2.36 2.51 -0.871910 1.62 0.99 0.11 2.85 2.40 -2.66 -0.60 -2.21 0.45 -0.471920 2.97 2.32 2.21 2.43 -0.02 0.18 -0.31 -0.49 1.43 -0.511930 1.46 -0.48 -0.60 -0.21 1.91 1.90 -1.00 -0.81 3.75 -0.661940 -1.78 -2.10 -0.84 3.31 0.71 -1.69 1.62 -2.73 0.68 1.531950 1.10 0.49 -1.54 1.50 3.26 -2.79 0.54 -0.51 -2.12 1.831960 -1.88 0.47 -1.05 -2.16 -1.04 -1.77 -2.54 1.67 -2.97 -2.581970 -1.08 -0.08 2.05 0.27 2.18 0.01 0.59 -2.08 -0.42 -0.231980 -1.58 -0.55 2.63 0.38 2.17 -3.09 3.14 -3.01 -0.13 2.381990 3.88 1.14 2.54 1.71 2.86 -1.11 -2.00 -0.93

Page 22: Northern Hemispheric Flow Indices

Monthly NAO during the Monthly NAO during the 1950s1950s

http://www.ldeo.columbia.edu/NAO/http://www.ldeo.columbia.edu/NAO/

1950 0.2 1.9 0.1 2.0 -3.0 0.3 0.5 2.4 4.4 1.6 -0.6 -2.0

1951 1.2 1.7 -2.6 -2.0 -2.6 -3.5 0.0 2.8 0.5 2.1 -0.2 3.8

1952 2.2 -1.6 -2.3 2.8 -2.7 -0.3 0.6 -0.9 -3.7 0.1 -2.8 -1.7

1953 -1.4 0.6 0.5 -3.2 -1.5 1.6 2.6 2.9 2.1 2.6 3.6 1.7

1954 0.0 1.9 0.9 0.8 -2.2 1.1 4.2 -0.2 2.5 1.8 3.5 2.2

1955 -2.5 -2.9 -3.2 1.1 -0.2 -0.3 2.3 2.2 5.4 -2.1 -4.0 -1.1

1956 -1.2 -2.9 0.8 -2.0 6.3 0.5 -1.6 -2.2 -1.2 1.3 2.4 2.3

Page 23: Northern Hemispheric Flow Indices

Viewing the NAOViewing the NAO

Best to look at westerlies and upper level Best to look at westerlies and upper level heightsheights– compare anomaliescompare anomalies

westerlies above (+) or below (-) normalwesterlies above (+) or below (-) normal position of upper level high/low systemsposition of upper level high/low systems

Large Negative NAO exampleLarge Negative NAO example– Jan 1956 Great Atlantic LowJan 1956 Great Atlantic Low– Huge upper level ridge over Greenland and Huge upper level ridge over Greenland and

LabradorLabrador– Strong trough off southeastern USStrong trough off southeastern US– Rex Block is another sign.Rex Block is another sign.

Page 24: Northern Hemispheric Flow Indices

Low NAO Storm ExampleLow NAO Storm Example

Page 25: Northern Hemispheric Flow Indices

NAO and HistoryNAO and HistoryMedieval warm periodMedieval warm period

Medieval warm period (800-1200 AD)Medieval warm period (800-1200 AD)– Vikings and Irish Monks traveled the North Vikings and Irish Monks traveled the North

AtlanticAtlantic– VikingsVikings

settled Iceland and Greenlandsettled Iceland and Greenland Farmed on Greenland and raised sheepFarmed on Greenland and raised sheep went to the Islands we now know as Labradorwent to the Islands we now know as Labrador obtained wood for ships in New Found landobtained wood for ships in New Found land sailed on low sea ice and not very stormy seassailed on low sea ice and not very stormy seas

Warmest summers in 8000 yearsWarmest summers in 8000 years

Page 26: Northern Hemispheric Flow Indices

NAO Detection from PastNAO Detection from Past

Wine recordsWine records– dates of grape harvests dates of grape harvests

late harvests, cold summerslate harvests, cold summers early harvests, warm summersearly harvests, warm summers

– location of vineyards…into Scotlandlocation of vineyards…into Scotland Wheat/Barley FaminesWheat/Barley Famines

– 800-1200 AD wheat grown higher latitudes and 800-1200 AD wheat grown higher latitudes and altitudes in Europealtitudes in Europe

– barley grown in Iceland (not today!)barley grown in Iceland (not today!)– bad wheat crops lead to faminesbad wheat crops lead to famines

Tree rings and ice core samplesTree rings and ice core samples

Page 27: Northern Hemispheric Flow Indices

Medieval warm period Medieval warm period endsends

Cold weather began to return slowly in Cold weather began to return slowly in 11th Century11th Century– some cold years; such as 1258 some cold years; such as 1258 – probably related to volcanismprobably related to volcanism– most of the time it was quite warm most of the time it was quite warm – 1258 was probably a low NAO year based 1258 was probably a low NAO year based

on tree rings in the region being narrow on tree rings in the region being narrow showing slow growthshowing slow growth

Page 28: Northern Hemispheric Flow Indices

The Little Ice Age beginsThe Little Ice Age begins Colder weather began to dominate in 12th Colder weather began to dominate in 12th

centurycentury– 1309/10 Thames river freezes with cold and dry 1309/10 Thames river freezes with cold and dry

weatherweather tree rings were narrow suggesting cold and dry tree rings were narrow suggesting cold and dry NAO < 0NAO < 0

– 1312 very wet; failed wheat crops (NAO>0)1312 very wet; failed wheat crops (NAO>0)– 1315 very wet for next 3 years1315 very wet for next 3 years

extraordinary tree ring growth in Iceland and Irelandextraordinary tree ring growth in Iceland and Ireland very wetvery wet lead to crop failures and the Great Faminelead to crop failures and the Great Famine

– some countries lost 5-10% of population in large townssome countries lost 5-10% of population in large towns

– 1320 NAO went negative and ended famine periods and 1320 NAO went negative and ended famine periods and wetness-Record cold set inwetness-Record cold set in

Page 29: Northern Hemispheric Flow Indices

The Little Ice AgeThe Little Ice Age1300 to ~18501300 to ~1850

General period was colder than today by General period was colder than today by 0.3C.0.3C.

Some particular cold decades about 0.5C Some particular cold decades about 0.5C coldercolder– virtually all linked to prolonged negative NAOvirtually all linked to prolonged negative NAO– warmer intervals linked to positive NAOwarmer intervals linked to positive NAO– some periods linked to:some periods linked to:

Maunder minimum - low to no sunspots observed Maunder minimum - low to no sunspots observed globallyglobally

Large volcanic eruptionsLarge volcanic eruptions

– Cold in Europe was linked to cold in North AmericaCold in Europe was linked to cold in North America America became settled in this time frameAmerica became settled in this time frame

Page 30: Northern Hemispheric Flow Indices

The Little Ice AgeThe Little Ice AgeColdest DecadesColdest Decades

1557-16001557-1600

– 1590 were coldest period1590 were coldest period– 1588- high NAO storm time…Spanish Armada..1588- high NAO storm time…Spanish Armada..

1690s 1690s

– heart of Maunder sunspot minimumheart of Maunder sunspot minimum

1810s1810s

Page 31: Northern Hemispheric Flow Indices

Identifying the Coldest Identifying the Coldest DecadesDecades

Ice cores cover the entire periodIce cores cover the entire period Tree rings cover the entire period (>300 Tree rings cover the entire period (>300

locations)locations) Volcanic dust layersVolcanic dust layers Reliable wine harvest data present to ~1400Reliable wine harvest data present to ~1400 Other records Other records

– local harvest and famine recordslocal harvest and famine records bad wheat harvest ~ high NAO index wet yearsbad wheat harvest ~ high NAO index wet years

– writings and art workwritings and art work

Page 32: Northern Hemispheric Flow Indices

Other NAO impacts on Other NAO impacts on ClimateClimate

VolcanismVolcanism– 1600 was notable year1600 was notable year

SunspotsSunspots– Sporer minimum 1460-1550Sporer minimum 1460-1550– Maunder minimum 1645-1715Maunder minimum 1645-1715

period of prolonged low sunspot activityperiod of prolonged low sunspot activity 1672-1704 no sun spots were observed1672-1704 no sun spots were observed

– correlated closely to cold period correlated closely to cold period – many low NAO yearsmany low NAO years– 1810 was a no sun spot year1810 was a no sun spot year– sun spots may be proven to impact Climate.sun spots may be proven to impact Climate.

Page 33: Northern Hemispheric Flow Indices

Pacific North American Pacific North American PattenPatten

Flow Pattern over North America Flow Pattern over North America and adjacent Pacific Oceanand adjacent Pacific Ocean

referred to as the PNAreferred to as the PNA . The standard is from Wallace and . The standard is from Wallace and

Gutzler (1981) where they defined Gutzler (1981) where they defined the index as: the index as:

time(yeartime(year)=[z(20N,160W)-z(45N,165W))=[z(20N,160W)-z(45N,165W)+z(55N,115W)+z(30N,85W)]/ 4+z(55N,115W)+z(30N,85W)]/ 4

Page 34: Northern Hemispheric Flow Indices

PNA DescriptionPNA Description The PNA pattern is one of the most prominent The PNA pattern is one of the most prominent

modes of low-frequency variability in the Northern modes of low-frequency variability in the Northern Hemisphere extra-tropics, appearing in all months Hemisphere extra-tropics, appearing in all months except June and July. except June and July.

The PNA pattern reflects a quadripole pattern of The PNA pattern reflects a quadripole pattern of height anomalies, with anomalies of similar sign height anomalies, with anomalies of similar sign located south of the Aleutian Islands and over the located south of the Aleutian Islands and over the southeastern United States. Anomalies with sign southeastern United States. Anomalies with sign opposite to the Aleutian center are located in the opposite to the Aleutian center are located in the vicinity of Hawaii, and over the intermountain vicinity of Hawaii, and over the intermountain region of North America (central Canada) during region of North America (central Canada) during the winter and fall/spring. the winter and fall/spring.

Page 35: Northern Hemispheric Flow Indices

PNA Plots PNA Plots (Nov-Mar)(Nov-Mar)

Page 36: Northern Hemispheric Flow Indices

Positive PNA-JanuaryPositive PNA-January

Page 37: Northern Hemispheric Flow Indices

Negative PNA-JanuaryNegative PNA-Januaryhttp://www.cdc.noaa.gov/USclimate/pna.htmlhttp://www.cdc.noaa.gov/USclimate/pna.html

Page 38: Northern Hemispheric Flow Indices

PNA QuadripolePNA Quadripole

Page 39: Northern Hemispheric Flow Indices

ConclusionsConclusions The The North Atlantic OscillationNorth Atlantic Oscillation (NAO) (NAO)

– Impacts the seasonal weather overImpacts the seasonal weather overeastern North America, western Europeeastern North America, western Europeand Greenlandand Greenland– Has two phases in the cold seasonHas two phases in the cold season

The The Pacific North American IndexPacific North American Index (PNA) (PNA)– Describes the primary mode of atmospheric Describes the primary mode of atmospheric

circulation pattern across North America and circulation pattern across North America and adjacent oceans.adjacent oceans.

– Related to teleconnections (Aleutian and Related to teleconnections (Aleutian and Southeast) and (Hawaii and Northern Rockies)Southeast) and (Hawaii and Northern Rockies)

Page 40: Northern Hemispheric Flow Indices

Web resourcesWeb resources

NAONAO http://www.ldeo.columbia.edu/NAO/http://www.ldeo.columbia.edu/NAO/ http://www.cru.uea.ac.uk/tiempo/floor2/data/http://www.cru.uea.ac.uk/tiempo/floor2/data/

nao.htmnao.htm http://www.cpc.noaa.gov/data/teledoc/http://www.cpc.noaa.gov/data/teledoc/

nao.htmlnao.html http://www.cdc.noaa.gov/USclimate/http://www.cdc.noaa.gov/USclimate/

pna.htmlpna.html

Page 41: Northern Hemispheric Flow Indices

ReferencesReferencesRogers, J.C., 1997: North Atlantic storm track variability and its association Rogers, J.C., 1997: North Atlantic storm track variability and its association

to the North Atlantic Oscillation and climate variability of Northern to the North Atlantic Oscillation and climate variability of Northern Europe. Europe. Journal of ClimateJournal of Climate 10(7)10(7), 1635-1647. , 1635-1647.

Hurrell, J.W., 1995: Decadal trends in the North Atlantic Oscillation and Hurrell, J.W., 1995: Decadal trends in the North Atlantic Oscillation and relationships to regional temperature and precipitation. relationships to regional temperature and precipitation. ScienceScience 269269, ,

676-679.676-679. Wallace, J.M. and David S. Gutzler, 1981:"Teleconnections in the Wallace, J.M. and David S. Gutzler, 1981:"Teleconnections in the

Geopotential Height Field during the Northern Hemisphere Winter" Geopotential Height Field during the Northern Hemisphere Winter" Mon. Mon. Wea. ReviewWea. Review,,109109,784-812. ,784-812.

Teleconnections Linking Wolrdwide Climate Anomalies. ed. M.H. Glantz, Teleconnections Linking Wolrdwide Climate Anomalies. ed. M.H. Glantz, R.W. Katz and N. Nicholls, Cambridge University Press, 1991. R.W. Katz and N. Nicholls, Cambridge University Press, 1991.

Rogers, J.C. and H. Van Loon, 1979: "The Sea-Saw in winter temperatures Rogers, J.C. and H. Van Loon, 1979: "The Sea-Saw in winter temperatures between Greenland and Northern Europe. Part II. Some atmospheric and between Greenland and Northern Europe. Part II. Some atmospheric and oceanic effectes in middle and high latitudes." oceanic effectes in middle and high latitudes." Mon Wea. Rev. Mon Wea. Rev. ,,107107, 509-, 509-519. 519.