Download Hurricanes - EnviroEcon

Reading Assignment
ATMOS1020ClimateChange
14.Hurricanes
ThomasReichler,Dept.ofAtmosphericSciences,April11,2016
— Youshouldread:
—
RoughGuidep.128-146,“Hurricanesandother
storms”
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Hurricanes and OtherStorms
— Howdohurricaneswork?
— Threatsfromhurricanes
— Willthere bemorehurricanesinthefuture?
— Tornadoes
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ProfileofaTropical Cyclone
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Katrina, August 282005
— Hurricane =typhoon =tropical
cyclone
— alldifferent wordsfor the
same thing
— Rising areashaverain &
clouds, sinking areasaredry
— Eye:clear& quiescent areain
thecenter (lowestpressure)
— Eyewall:clouds immediately
surrounding eye(highest
winds &rain)
— Spiralrain bands: outer
rainingareas
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EyeofKatrina
Worldwide Hurricane Tracks
— Katrinacausedimmensedamage andfloodingandkilled
over1800people
— The cityofNewOrleanswasallbutdestroyedbythe
hurricane,andtheentire citywassubsequentlyordered
tobeevacuated
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Saffir-Simpson Hurricane Scale
— Highercategory
= lowerpressure
intheeye
= higherwinds
= morestorm
surge
= moredamage
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CycloneYasi
— Hurricanesoccuroverthewarmestwaters…
— Butnotrightattheequator!(Coriolisforceisrequired)
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Tropical CycloneYasi
— Landfallinnorthern
Queenslandon3February
2011
— 155mphwinds,930mbar
min.pressure
— Amongtop10tropical
cyclonestohitAustralia
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Tracks ColoredbyCategory
— LaNina:Extremely warm (30-
32⁰C)oceantemperaturesover
westernPacific
Only10% of
theworld’s
hurricanes
occurinthe
Atlantic
— ManystrongeststormsarearoundTaiwan,Philippines
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Condensational Heating
— Whenitrains,water condenses,i.e.,itchangesphase
fromvaportoliquid
— Duringthisprocess,energycontainedinthevaporis
released; theenergy iscalledlatentheat
— The heatisproportionaltotheamountofrainfall
— Heatrelease fromahurricane
1.5cm/dayofrainfallinacircleofradius660km
— theheat releasedfromthiscondensationis52
quintillion(10 18)Joulesperdayofenergy
— 200timestheworldelectricitygeneratingcapacity!
—
— There’s atremendousamountofenergyinahurricane…
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Evaporation andCondensation
— Ahurricane’senergycomes
fromtheocean
— Evaporation atocean
surfaceprovidesthefuel
— strongwindsin
hurricanescausemore
evaporationfromthe
oceansurface
— Thewarmer,thebetter
— evaporationoccurs
moreeasilyfroma
warmer ocean
— warmer aircanhold
muchmoremoisture
— Condensation andcloud
formationinthehurricane
releases energy tothe
atmosphere>winds
RequirementsforHurricanes
1. Sea surfacetemperaturesmustbeabove26 oC(79 oF)
—
thismayshifttoawarmertemperature thresholdina
warmer climate though
2. Mustbeatleast5degreesofftheequator
—
Coriolisforceisrequired(Coriolisforceiswhystorms
rotateoppositeinNorthernandSouthern
Hemispheres)
3. Notmuchwindshear
windshear:when thewindschangewithheight
— thisripshurricanesapart
—
334 joules/g = 80 calories/g
— Warmoceantemperatures:first
requirement forhurricanes
— Hurricanesweaken whentheypassover
landorawayfromtheTropicsdueto
lackofevaporation
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Sub-Surface Temperatures
— Whenhurricanespass
by,they churnup
colderwater from
below
— Youcanseea cold
wake inthesurface
temperature behind
hurricanes
— Here, hurricaneKatrina
churnsupcoldwaters
andleavesa coldwake
4. Can’tbetoocoldbelowtheoceansurfaceeither
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ColdOcean inKatrina’s Wake
Hurricane Damages
— Damagesinhurricanesarecausedby:
—
winds
stormsurge
—
heavyrain andflooding
—
—
highwindspushingwatertowardstheland
— Financialdamages fromhurricanesisincreasing,butthis
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isprimarilyduetomorepeoplelivingonthecoast
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WindDamage
Storm Surge
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Flooding
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1991Bangladesh Cyclone
— 144,000fatalities,left10millionhomeless
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2008Myanmar CycloneNargis
— Nargis struckMyanmaronMay
2,2008
— Lossof78,000peopleand
affected2.4millionothers
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Hurricanes and GlobalWarming
— Warmer temperaturesmean:
warmer ocean, theultimatereservoir ofhurricane
energy
— morewater vaporintheair
— water vaporislikegasolineforhurricanes
—
— Shouldn’tthismeanstrongerstorms?
— Yes, butit’snotsosimple…
HaveHurricanes BeenChanging?
— In2005intheAtlantic,therewere:
—
— Aprediction from a
computer model of global
warming
— Increased shear overthe
Gulf of Mexico would act
toweaken hurricanes
— would offset some of
theincrease instrength
due toincreased
temperatures …
— Alsotheatmosphere tends
tostabilize when there’s
more moisture
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—
Shears CanChange …
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RecentChangesinHurricanesWorldwide
— Recentstudyclaimsthatstrongesth.haveincreased:
3of6strongeststormsever(Wilma,Rita,andKatrina)
27namedstorms(smashingthepreviousrecordof21)
—
—
ranoutoflettersinthealphabet
— Q,U,X,YandZarenotused…
hadtouseAlpha,Beta,Gamma,Delta,Epsilon,andZeta
— Butweknowbetter tosaythatoneanomalousseasonis
Webster et al. (2005)
duetoglobalwarming…
— plus,only10%oftheworld’shurricanesoccurinthe
Atlantic
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— Claimscat.4&5haveincreased by50%
RecentChangesinHurricanesWorldwide
RecentChangesinHurricanesWorldwide
— Emanuel (2005)
— Observationalrecordwith
fullcoverageisrelatively
shortthough
— Powerdissipationindex
(PDI):bettermeasureof
hurricanesthatcombines
number,intensity and
duration
— Beforethe1970swe
didn’thavesatellitedata
— PaperbyChrisLandsea
— PDIintheAtlanticishighly
arguesthatoverthelong
term, recording
instrumentschanged,not
hurricanes
correlatedwithAtlantic
Oceantemperatures
— Thisstudysuggeststhat
hurricaneswillcontinueto
strengthenwithglobal
warming
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ObservedHurricane Changes
RecentChangesinHurricanesWorldwide
— Studyby:Maue
— Debatewasrather heatedforawhile
(2011,GRL)
— Resultsarestillsomewhatcontentious
— Globaltropical
— Fundamentalproblemisthattheobservedrecordis
cyclone
accumulated
energy (ACE)
short andthathurricanesarerelativelyrare events
— Howaboutcomputermodelingresults?
— Considerableups
anddowns
—
— Swingsare mostly — Decrease since record highfrom 2005
duetonatural
— No distinction between weakand
variability(ENSO
stronghurricanes
andPDO) ATMOS1020,ClimateChange,Thomas Reichler,U nivers ityofUtah,31
SimulatedHurricane Changes
theseare difficulttoo:globalclimatemodelsaren’t
highenoughresolutiontocapturehurricaneswell
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Hurricanes Q&A
— CanindividualhurricaneslikeKatrinabeattributedtoglobal
— Recentmodelresultsare
suggestingfewerbut
moreintensestorms
← Weaker
Stronger →
Knutson and Tuleya (2004)
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MoreTornadoes?
warming?
— No!
— Canitbesaidthatglobalwarmingmadeanindividualhurricane
likeKatrinastrongerthanitwouldhaveotherwisebeen?
— Perhaps.Itisbelievedthatwarmeroceanssupplymoreenergy
tohurricanesandthusleadtostrongerhurricanes.Also,a
warmeratmospherecanholdmoremoisture,potentially
leadingtomoreenergyrelease.
— Havehurricanesbecomemoreintense?
— TheevidencefortheAtlanticissuggestive,butnotconclusive
atthispoint.Globally:no
— Shouldweexpectthathurricaneswillbecomemoreintense?
— Yes.Heavierrains,strongerwinds,strongerstormsurges.
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MoreTornadoesWithGlobalWarming?
— Same issueaswithhurricanes
— Hardtoprovetheexistenceoftrends
— There isreasontobelievethatstorms thatderive
energy fromthecondensationofwatervapor(release
of“latentheat”)willbemoreintenseinawarmer
worldwithmoreatmosphericwater vapor
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Summary ofFutureofHurricanes
— Dataseemstoshowanincreaseinstrength,in
particularoverAtlantic
— somearguethatdata qualityisnotgoodenoughto
make thecasethough
— Modelssuggestthestrongeststormswillbecomemore
frequent andstronger
— butalsoareductioninthetotalnumberofstorms
— Shouldbemuchscientificprogressinthisfieldoverthe
nextdecade!
— asmodelresolutionincreasesandwegetmoredata
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