Download Chapter 14 Cold Waves Effects of Cold Waves

2/11/17
Chapter14
Cold Waves
Cold Waves
• Aninflux ofunusually cold airfromthearctic
thatintrudes into thelower andmiddle
latitudes
• Canfreezevegetationandcausestructural
damage
• Generally affectmuchlarger areasthan
blizzards, icestorms, etc.
EffectsofCold Waves
• NWSkeepsstatistics ondeathsrelated tocold
weather outbreaks
– Onaverage, (3,30,300)deathsareattributedto
coldwaves
• CDC estimatesthat(60, 600,6000)deaths are
attributed tohypothermia
– Maynotnecessarilyberelatedtoacoldoutbreak
– Onlyincludesdeathsdirectlyrelatedtocold
– Disproportionatelyoccuramongstelderlymales
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Cold Waveoutbreaks
• Whereareeconomic lossesgreatest?
• Whatismeantbya“Cold Wave”?
Cold WaveIntensityMeasure
• Temperatures during cold wavesarenot the
mostmeaningful measureofacold waves
intensity. Whatis?
LowestTemperaturesonRecordby
State
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Cold WaveDevelopment
• Core developsasastrong(high-pressure/lowpressure) systemathighlatitudes
• Aircools neartheground byconductive heat
losstotheground
• Airdensity increases, temperature decreases,
whathappens topressure?
• Whattypeofairmass develops?
ArcticAir
• Temperatures intheArctic Regions can
sometimes drop below -40C.Whatproblems
doesthis cause?
DevelopmentofPolarAirmasses
• Whatistypicallycolder, Arctic Oceanregions
nearthepole orland locations (Siberia,
Northern Canada, Alaska)?Why?
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PolarAirmass Depths
• Generally shallow
• Characterized bystrongtemperature
inversions
• Canleadtotemperatures atthesurfacethat
are(5,10,15)Ccolder than severalhundred
metersaloft
• Howdoes topography playarole inin
enhancing temperature inversions?
Airmass Intensification
• Whatother factors canintensify theairmass?
Airmass Intensification
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Cold WaveOutbreaks
• Cold airoutbreaks require acoldairmass to
formathighlatitudes andmovesouth
• Whatmakesthemmove(twofactors)?
• Themorequickly itmovestomiddle latitudes,
thelesstimeithastomodify
Equatorward Motion
• Occur whenjetstream windshaveasoutherly
component
– Upperairpatterncontributestobothconvergence
aloftandsouthernmovementoftheairmass
• Factorofridge intensification overeastern
North Pacific
RidgeIntensification
• AiroverNorth PacificWatersis
(warmer/colder) thanairoverland atsame
latitudes
• Aleutian lowtransports warmairnorthward
• Northward flowofmaritime airleadsto
warming ofthelower troposphere. Whatdoes
thisdo tothejetstream?
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RidgeIntensification
• Second factorisflowassociated with strong
cyclones originating ontheeastsideofthe
Rockiesor alongtheeastern Seaboard
• Cyclones transport cold airsouthward ontheir
(eastern/western) side
• Enhances southward component ofjet stream
flowon troughs western side,enhancing
upstream ridge
Cold WavePattern
Cold WaveMovement
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Subsidence Effects
• Howdoes subsidence modify theairmass?
• Cancold airmasses passovertherockies and
headwest?
• Whatother variables canaffectcold wave
outbreaks?
Cold OutbreakSummary
• Whatfivefactors influence theoutbreak ofa
cold wave?
ExtremeCold inEuropeandAsia
• Siberia
– Whatenhancestheextreme coldinSiberia?
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NorthAtlanticOscillation
• Typicalflowiswesttoeast
• Flowisconsequence oftheIcelandic lowand
highpressure near theAzores
• Both pressure centers weakeningsubstantially
leadstotheNAO
• Allows coldSiberian airtomove
southwestward
NorthAtlanticOscillation
NorthAtlanticOscillation
• Negativephasewhenpressures andwinds are
allweakerthan normal
• Positive whenallarestronger
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EuropeanCold Outbreaks
Wind Chill Factor
• Accounts forthe effectoftemperature and
wind ontherateatwhich exposed skinwill
cool
• Solid andliquid surfaces loseheatmore
rapidly atagivenwind speedaswinds
increase
• Object losesheatduetoconduction
• Evaporation fromskinalsoincreases aswind
speedincreases
Wind Chill Index
• Estimateofperceived temperature basedon
wind speedandactual temperature
• Scientists first begandevelopment in1940’s,
where at?
• Measuredtime required forcooling and
freezing ofknown volumesofwaterstarting at
varioustemperatures
• Latestrefinement madein2001
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Wind Chill IndexModifications
• 2001adjustments included factorsaccounting
for:
– Advancesinscience,techandmodelingofheat
loss
– New formulabasedonmodelofhumanface
– Assumesnighttime,doesn’taccountforsunshine
warmth
Wind Chill Index
Advisory vs Watch
• Whatisthedifference between aWind Chill
AdvisoryandaWind Chill Warning?
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Cold WaveWarning
• Issuedbasedonforecastofprolonged
temperatures wellbelow normal
Cold WavesandClimateChange
• Whathazardsareassociated with coldwave
outbreaks?
• Whatwill climate changemeanforcoldwave
outbreaks?
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