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Chapter14

ColdWaves

ColdWaves

• Aninflux ofunusually cold airfromthearcticthatintrudes into thelower andmiddlelatitudes

• Canfreezevegetationandcausestructuraldamage

• Generally affectmuchlarger areasthanblizzards, icestorms, etc.

EffectsofColdWaves

• NWSkeepsstatistics ondeathsrelated tocoldweather outbreaks– Onaverage, (3,30,300)deathsareattributedtocoldwaves

• CDC estimatesthat(60, 600,6000)deaths areattributed tohypothermia–Maynotnecessarilyberelatedtoacoldoutbreak– Onlyincludesdeathsdirectlyrelatedtocold– Disproportionatelyoccuramongstelderlymales

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ColdWaveoutbreaks

• Whereareeconomic lossesgreatest?

• Whatismeantbya“Cold Wave”?

ColdWaveIntensityMeasure

• Temperatures during cold wavesarenot themostmeaningful measureofacold wavesintensity.Whatis?

LowestTemperaturesonRecordbyState

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ColdWaveDevelopment

• Core developsasastrong(high-pressure/low-pressure) systemathighlatitudes

• Aircools neartheground byconductive heatlosstotheground

• Airdensity increases, temperature decreases,whathappens topressure?

• Whattypeofairmass develops?

ArcticAir

• Temperatures intheArctic Regions cansometimes drop below -40C.Whatproblemsdoesthis cause?

DevelopmentofPolarAirmasses

• Whatistypicallycolder, Arctic Oceanregionsnearthepole orland locations (Siberia,Northern Canada, Alaska)?Why?

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PolarAirmass Depths

• Generally shallow• Characterized bystrongtemperatureinversions

• Canleadtotemperatures atthesurfacethatare(5,10,15)Ccolder than severalhundredmetersaloft

• Howdoes topography playarole ininenhancing temperature inversions?

Airmass Intensification

• Whatother factors canintensify theairmass?

Airmass Intensification

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ColdWaveOutbreaks

• Cold airoutbreaks require acoldairmass toformathighlatitudes andmovesouth

• Whatmakesthemmove(twofactors)?

• Themorequickly itmovestomiddle latitudes,thelesstimeithastomodify

EquatorwardMotion

• Occur whenjetstream windshaveasoutherlycomponent– Upperairpatterncontributestobothconvergencealoftandsouthernmovementoftheairmass

• Factorofridge intensification overeasternNorth Pacific

RidgeIntensification

• AiroverNorth PacificWatersis(warmer/colder) thanairoverland atsamelatitudes

• Aleutian lowtransports warmairnorthward• Northward flowofmaritime airleadstowarming ofthelower troposphere. Whatdoesthisdo tothejetstream?

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RidgeIntensification

• Second factorisflowassociated with strongcyclones originating ontheeastsideoftheRockiesor alongtheeastern Seaboard

• Cyclones transport cold airsouthward ontheir(eastern/western) side

• Enhances southward component ofjet streamflowon troughs western side,enhancingupstream ridge

ColdWavePattern

ColdWaveMovement

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Subsidence Effects

• Howdoes subsidence modify theairmass?

• Cancold airmasses passovertherockies andheadwest?

• Whatother variables canaffectcold waveoutbreaks?

ColdOutbreakSummary

• Whatfivefactors influence theoutbreak ofacold wave?

ExtremeCold inEuropeandAsia

• Siberia–WhatenhancestheextremecoldinSiberia?

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NorthAtlanticOscillation

• Typicalflowiswesttoeast• Flowisconsequence oftheIcelandic lowandhighpressure near theAzores

• Both pressure centers weakeningsubstantiallyleadstotheNAO

• Allows coldSiberian airtomovesouthwestward

NorthAtlanticOscillation

NorthAtlanticOscillation

• Negativephasewhenpressures andwinds areallweakerthan normal

• Positive whenallarestronger

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EuropeanColdOutbreaks

WindChill Factor

• Accounts forthe effectoftemperature andwind ontherateatwhich exposed skinwillcool

• Solid andliquid surfaces loseheatmorerapidly atagivenwind speedaswindsincrease

• Object losesheatduetoconduction• Evaporation fromskinalsoincreases aswindspeedincreases

WindChill Index

• Estimateofperceived temperature basedonwind speedandactual temperature

• Scientists first begandevelopment in1940’s,where at?

• Measuredtime required forcooling andfreezing ofknown volumesofwaterstarting atvarioustemperatures

• Latestrefinement madein2001

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WindChill IndexModifications

• 2001adjustments included factorsaccountingfor:– Advancesinscience,techandmodelingofheatloss

– Newformulabasedonmodelofhumanface– Assumesnighttime,doesn’taccountforsunshinewarmth

WindChill Index

Advisory vs Watch

• Whatisthedifference between aWind ChillAdvisoryandaWind Chill Warning?

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ColdWaveWarning

• Issuedbasedonforecastofprolongedtemperatures wellbelow normal

ColdWavesandClimateChange

• Whathazardsareassociated with coldwaveoutbreaks?

• Whatwill climate changemeanforcoldwaveoutbreaks?