Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
2/11/17
1
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
2/11/17
2
ColdWaveoutbreaks
• Whereareeconomic lossesgreatest?
• Whatismeantbya“Cold Wave”?
ColdWaveIntensityMeasure
• Temperatures during cold wavesarenot themostmeaningful measureofacold wavesintensity.Whatis?
LowestTemperaturesonRecordbyState
2/11/17
3
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?
2/11/17
4
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
2/11/17
5
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?
2/11/17
6
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
2/11/17
7
Subsidence Effects
• Howdoes subsidence modify theairmass?
• Cancold airmasses passovertherockies andheadwest?
• Whatother variables canaffectcold waveoutbreaks?
ColdOutbreakSummary
• Whatfivefactors influence theoutbreak ofacold wave?
ExtremeCold inEuropeandAsia
• Siberia–WhatenhancestheextremecoldinSiberia?
2/11/17
8
NorthAtlanticOscillation
• Typicalflowiswesttoeast• Flowisconsequence oftheIcelandic lowandhighpressure near theAzores
• Both pressure centers weakeningsubstantiallyleadstotheNAO
• Allows coldSiberian airtomovesouthwestward
NorthAtlanticOscillation
NorthAtlanticOscillation
• Negativephasewhenpressures andwinds areallweakerthan normal
• Positive whenallarestronger
2/11/17
9
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
2/11/17
10
WindChill IndexModifications
• 2001adjustments included factorsaccountingfor:– Advancesinscience,techandmodelingofheatloss
– Newformulabasedonmodelofhumanface– Assumesnighttime,doesn’taccountforsunshinewarmth
WindChill Index
Advisory vs Watch
• Whatisthedifference between aWind ChillAdvisoryandaWind Chill Warning?
2/11/17
11
ColdWaveWarning
• Issuedbasedonforecastofprolongedtemperatures wellbelow normal
ColdWavesandClimateChange
• Whathazardsareassociated with coldwaveoutbreaks?
• Whatwill climate changemeanforcoldwaveoutbreaks?