Air-Sea Interaction - Laws and Mechanisms

247 Pages·2004·4.172 MB·English

by  G. T. Csanady

Air-Sea Interaction
Air-SeaInteraction: LawsandMechanismsprovidesacomprehensiveaccountof
howtheatmosphereandtheoceaninteracttocontroltheglobalclimate,what
physicallawsgovernthisinteraction,andwhatareitsprominentmechanisms. In
recentyears,air-seainteractionhasemergedasasubjectinitsownright,
encompassingsmall-andlarge-scaleprocessesinbothairandsea.
Anovelfeatureofthebookisthetreatmentofempiricallawsofmomentum,
heat,andmasstransfer,acrosstheair-seainterfaceaswellasacrossthermoclines,
aslawsofnonequilibriumthermodynamics,withfocusonentropyproduction.
Thermodynamicsalsounderliesthetreatmentoftheoverturningcirculationsofthe
atmosphereandtheocean. Highlightsarethermodynamiccycles,theimportant
functionof“hottowers”indryingoutofmoistair,andoceanicheattransport
fromthetropicstopolarregions. Bydevelopingitssubjectfrombasicphysical
(thermodynamic)principles,thebookisbroadlyaccessibletoawideaudience.
Thebookismainlydirectedtowardgraduatestudentsandresearchscientistsin
meteorology,oceanography,andenvironmentalengineering. Thebookalsowill
beofvalueonentrylevelcoursesinmeteorologyandoceanography,andtothe
broaderphysicscommunityinterestedinthetreatmentoftransferlaws,and
thermodynamicsoftheatmosphereandocean.
GabrielCsanadyisProfessorEmeritusandformerholderofanendowedSlover
ChairofOceanographyinOldDominionUniversity,Norfolk,VA.Healsoserved
asaseniorscientistatWoodsHoleOceanographicInstitutionandaschairmanof
theDepartmentofMechanicalEngineeringattheUniversityofWaterloo. Hehas
beenaneditoroftheJournalofGeophysicalResearchandfounder-editorof
ReidelMonographsonEnvironmentalFluidMechanics. Heisauthorofthree
books: TheoryofTurbomachines(1964,McGraw-Hill),TurbulentDiffusioninthe
Environment(1973,D.ReidelPublishingCompany),andCirculationinthe
CoastalOcean(1982,D.ReidelPublishingCompany).

Air-Sea Interaction
Laws and Mechanisms
G. T. Csanady
Old Dominion University
Illustrations prepared by
Mary Gibson, Toronto
         
The Pitt Building, Trumpington Street, Cambridge, United Kingdom
  
The Edinburgh Building, Cambridge CB2 2RU, UK
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http://www.cambridge.org
©Cambridge University Press 2004
First published in printed format 2001
ISBN 0-511-03180-7 eBook (Adobe Reader)
ISBN 0-521-79259-2 hardback
ISBN 0-521-79680-6 paperback
Contents
Chapter 1 TheTransferLawsoftheAir-SeaInterface 1
1.1 Introduction 1
1.2 Flux and Resistance 3
1.2.1 Momentum Transfer in Laminar Flow 4
1.3 Turbulent Flow Over the Sea 7
1.3.1 Turbulence, Eddies and Their Statistics 7
1.3.2 The Air-side Surface Layer 9
1.3.3 Properties of the Windsea 11
1.4 Flux and Force in Air-Sea Momentum Transfer 13
1.4.1 Charnock’s Law 14
1.4.2 Sea Surface Roughness 14
1.4.3 Energy Dissipation 15
1.4.4 Buoyancy and Turbulence 17
1.5 The Evidence on Momentum Transfer 21
1.5.1 Methods and Problems of Observation 21
1.5.2 The Verdict of the Evidence 22
1.5.3 Other Influences 25
1.6 Sensible and Latent Heat Transfer 28
1.6.1 Transfer of “Sensible” Heat by Conduction 29
1.6.2 Transfer of Water Substance by Diffusion 31
1.6.3 Heat and Vapor Transfer in Turbulent Flow 32
1.6.4 Buoyancy Flux Correction 35
vi Contents
1.6.5 Observed Heat and Vapor Transfer Laws 36
1.6.6 Matrix of Transfer Laws 40
1.6.7 Entropy Production 41
1.7 Air-Sea Gas Transfer 44
1.7.1 Gas Transfer in Turbulent Flow 45
1.7.2 Methods and Problems of Observation 46
1.7.3 The Evidence on Gas Transfer 48
Chapter 2 WindWavesandtheMechanismsofAir-SeaTransfer 51
2.1 The Origin of Wind Waves 51
2.1.1 Instability Theory 54
2.1.2 Properties of Instability Waves 56
2.2 The Wind Wave Phenomenon 59
2.2.1 Wave Measures 62
2.2.2 Wave Growth 66
2.2.3 The Tail of the Characteristic Wave 71
2.2.4 Short Wind Waves 74
2.2.5 Laboratory Studies of Short Waves 76
2.3 The Breaking of Waves 81
2.3.1 Momentum Transfer in a Breaking Wave 82
2.4 Mechanisms of Scalar Property Transfer 86
2.4.1 Water-side Resistance 87
2.4.2 Air-side Resistance 90
2.5 Pathways of Air-Sea Momentum Transfer 92
Chapter 3 MixedLayersinContact 97
3.1 Mixed Layers, Thermoclines, and Hot Towers 97
3.2 Mixed Layer Turbulence 100
3.3 Laws of Entrainment 104
3.3.1 Entrainment in a Mixed Layer Heated from Below 105
3.3.2 Mixed Layer Cooled from Above 108
3.3.3 Shear and Breaker Induced Entrainment 110
3.4 A Tour of Mixed Layers 115
3.4.1 The Atmospheric Mixed Layer Under the Trade Inversion 116
3.4.2 Stratocumulus-topped Mixed Layers 120
3.4.3 Oceanic Mixed Layers 124
3.4.4 Equatorial Upwelling 129
3.5 Mixed Layer Interplay 132
3.5.1 Mixed Layer Budgets 133
Contents vii
3.5.2 Atmospheric Temperature and Humidity Budgets 136
3.5.3 Oceanic Temperature Budget 136
3.5.4 Combined Budgets 137
3.5.5 Bunker’s Air-Sea Interaction Cycles 140
Chapter 4 HotTowers 146
4.1 Thermodynamics of Atmospheric Hot Towers 147
4.1.1 The Drying-out Process in Hot Towers 148
4.1.2 The Thermodynamic Cycle of the Overturning Circulation 152
4.2 Ascent of Moist Air in Hot Towers 158
4.2.1 Hot Tower Clusters 160
4.2.2 Squall Lines 164
4.3 Hurricanes 167
4.3.1 Entropy Sources in Hurricanes 172
4.3.2 Thermodynamic Cycle of Hurricanes 175
4.4 Oceanic Deep Convection 178
4.4.1 Observations of Oceanic Deep Convection 181
Chapter 5 TheOcean’sWarmWaterSphere 187
5.1 Oceanic Heat Gain and Loss 189
5.1.1 Mechanisms of Heat Gain 194
5.2 Oceanic Heat Transports 197
5.2.1 Direct Estimates of Heat Transports 198
5.2.2 Syntheses of Meteorological Data 199
5.3 Warm to Cold Water Conversion in the North Atlantic 204
5.3.1 Cold to Warm Water Conversion 205
5.4 The Ocean’s Overturning Circulation 208
5.4.1 The Role of the Tropical Atlantic 211
5.4.2 Heat Export from the Equatorial Atlantic 213
5.5 What Drives the Overturning Circulation? 216
5.5.1 CAPE Produced by Deep Convection 217
5.5.2 Density Flux and Pycnostads in the North Atlantic 219
References 225
Index 237

Chapter1
The Transfer Laws of the Air-Sea Interface
1.1 Introduction
HurricaneEdouardhadjustpassedbyCapeCodwhenIwrotetheselines,aftergiving
usagoodscare,andkeepingmeteorologistsoflocalTVstationsoutofbedallnight.
ApproachingonatrackalongtheEastCoast,Edouardremainedacategory3hurricane,
with180km/hwinds,fromthetropicstolatitude38◦N.Thisiswhereitleftthewarm
watersoftheGulfStreambehind,quicklytoloseitspunchoverthemuchcoolerMid
AtlanticBight,andtobedegradedtocategory1,with130km/hwinds,stillenough
touprootafewtreesontheCape.
Edouard’sfurycamefromwatervapor,asitascendsthe“eye-walls”(Figure1.1)
thatsurroundahurricane’score,condensingandreleasingitslatentheatofevaporation.
Theheatmakesthemoistairbuoyant,turningtheeyewallsintoagiantchimneywith
anincrediblystrongdraft.Thedraftsucksinsea-levelair,causingittospiraltoward
thecoreindestructivewindsandtodrivewatersagainstnearbycoastsinstormsurges.
The fast air flow over warm water also ensures intense heat and vapor transfer to
theair,sustainingthehurricane’sstrength.Overcolderwater,wherenotenoughwater
evaporates,thehurricanedies:Thelifebloodofahurricaneisintenseseatoairtransfer
ofheatandwatervapor.Ontheotherhand,ashurricanewindswhipthewatersalong,
they transfer some of their momentum downward. The loss of momentum acts as a
brakeonthehurricanecirculation,keepingthewindsfromcompletelygettingoutof
hand.
Ahurricanealsomimicsonasmall-scaletheglobalatmosphericcirculation,which
issimilarly“fueled”bylatentheatreleasedfromcondensingwatervapor.Thishappens
in“hottowers,”concentratedupdraftsoftheInterTropicalConvergenceZone(ITCZ),
andalsoinsomewhatlessvigorousupdraftswithinextratropicalstorms.Manyofthe
2 TheTransferLawsoftheAir-SeaInterface
Figure1.1 Meanstructureofamaturehurricane(“Helene,”26Sept.1958)incrosssection,
supposingaxialsymmetry.Theleft-handhalfshowstheboundariesoftheeye-wall(solidlines,
bendingoutwardwithheight)andillustratesthecloudstructure.Thebrokenlinesarecontours
ofconstant“equivalentpotentialtemperature,”theabsolutetemperatureindegreesKelvinthat
theairwouldhavewithallofthelatentheatinitsvaporcontentreleased,andthepressure
broughtdowntosealevelpressure.Intheright-handhalfsection,thinfulllinesarecontoursof
constantwindspeedinms−1(thethicklinesrepeattheeyewallboundaries),thebrokenlinesare
angularmomentumcontours,thedottedlinescontoursoftemperaturein◦C.Themaximum
windspeedisinexcessof180km/h.Notethestratiformcloud(dashedlinesinthelefthalf)
extendingto13kmheight,tothetopofthetroposphere,wherethetemperatureis−55◦C,
=218K.Satellitesseethis“cloud-top”temperature.FromPalme´nandNewton(1969).
latterdrawtheirvaporsupplyfromthewarmGulfStreamanditsPacificcounterpart,
theKuroshio,oceancurrentstransportingmassiveamountsofheatfromwarmtocold
regions.Hottowersmaketheirpresenceknowntotravelerscrossingtheequator,and
wake them from their slumber when updrafts toss around their jetliner, as high as
10or12kmabovesealevel.Heatreleaseintheupdrafts,andcompensatingcooling
andsubsidence,arepartofathermodynamiccyclethatenergizesvariousatmospheric
circulationsystems,includingtheeasterlywindsofthetropicsandsubtropics,andthe
westerliesofmid-latitudes.Thewindsinturnsustainseatoairheatandvaportransfer,
supplying the fuel, moist air, for the updrafts. The associated air to sea transfer of
momentum from the winds is again the control on the strength of the atmospheric
circulation.
Importanttotheoperationofhurricanesandtolarge-scaleatmosphericandocean
circulationsystemsisthereforeinwhatamount,andbywhatmechanisms,momentum,
heatandvaporpassfromonemediumtotheother.Theratesoftransfer,perunittime