11

Tim Oke and the extension-upwards of Tim Oke and the extension-upwards of UHI-observations into the PBL UHI-observations into the PBL

Prof. Robert BornsteinProf. Robert Bornstein

Dept. of Meteorology, San Jose State UniversityDept. of Meteorology, San Jose State University

San Jose, CA, USA, San Jose, CA, USA, pblmodel@hotmail.com

Prof. Julian HuntProf. Julian Hunt

University College, London, UKUniversity College, London, UK

Presented at thePresented at theT. R. Oke SymposiumT. R. Oke Symposium

AMS Annual Meeting, Phoenix AZAMS Annual Meeting, Phoenix AZJan 2009Jan 2009

Funding source: Funding source: NSFNSF

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OVERVIEW• URBAN CLIMATE ELEMENTS: URBAN CLIMATE ELEMENTS: a reviewa review• TIM OKE’S TIM OKE’S (and his group)(and his group) PBL-UHI work PBL-UHI work

– ObservationsObservations– Explanations Explanations – Impacts on other urban-PBL climate Impacts on other urban-PBL climate

elementselements

• Synthesis of ideas from Synthesis of ideas from – PBL observations PBL observations (Oke and his group)(Oke and his group)– Analytical fluid dynamics Analytical fluid dynamics (work of Prof. Hunt)(work of Prof. Hunt)– Urbanized meso-met models Urbanized meso-met models (Bornstein & (Bornstein &

many other groups)many other groups)

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uPBL CLIMATE ELEMENTS:uPBL CLIMATE ELEMENTS:battles between conflicting battles between conflicting

effectseffectsMonatomic effectsMonatomic effects• VISIBILTITY:VISIBILTITY: decreased decreased• TURBULENCE:TURBULENCE: increased (mechanical & thermal) increased (mechanical & thermal)• PBL NIGHT STABILITY:PBL NIGHT STABILITY: neutral neutral• FRONTS (synoptic & sea breeze):FRONTS (synoptic & sea breeze): slowed slowed

More complex effectsMore complex effects• TEMP:TEMP: increased (UHI) or decreased increased (UHI) or decreased• MOISTURE:MOISTURE: increased or decreased increased or decreased• WIND SPEED (V):WIND SPEED (V): increased or decreased increased or decreased• WIND DIRECTION:WIND DIRECTION: convergence or divergenceconvergence or divergence• PRECIP:PRECIP: increased or decreased increased or decreased• THUNDERSTORMS:THUNDERSTORMS: triggered or split triggered or split

44

PBL scales & layers (modified after Oke, 1997)

UBL

UCL UCL

RSL

RSL

55

uPBL sub-layersuPBL sub-layers• Urban mixing layerUrban mixing layer

– Non-homogeneous Non-homogeneous – Non-stationaryNon-stationary

• Urban SfcBL:Urban SfcBL: has several sub-layers has several sub-layers (next slide) (next slide) • Urban surface:Urban surface: where is it in urban meso-met where is it in urban meso-met

models:models:– groundground– roughness length, zroughness length, zoo

– rooftoprooftop– displacement height, ddisplacement height, d– top of roughness sub-layer (RSL) top of roughness sub-layer (RSL)

• Urban sub-surface:Urban sub-surface: consists of consists of – groundground– wallswalls– roofsroofs

66

Integration of all surface temperatures gives ‘the’ SUHI

“Surface” temperatures and ‘the’ Sfc UHI (SUHI): from Oke 2008

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uSfcBL sub-layersuSfcBL sub-layers• Urban Canopy Layer (UCL)Urban Canopy Layer (UCL)

– Between buildings (extends from 0-h)Between buildings (extends from 0-h)– Flow pattern is f (W/h ratio) Flow pattern is f (W/h ratio)

skimming, vortex, or isolated-obstacle skimming, vortex, or isolated-obstacle flowflow

• Roughness sub-layer, RSLRoughness sub-layer, RSL – Flux-blending layer (extends from h to 3h)Flux-blending layer (extends from h to 3h)

– M-O theory M-O theory not validnot valid, as u, as u**(z)(z)

• Inertial sub-layer Inertial sub-layer (Oke’s tower obs)(Oke’s tower obs) – Fluxes have blended (>3h)Fluxes have blended (>3h)

– M-O theory M-O theory is validis valid, as u, as u* * not f(z)not f(z)

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St. Louis St. Louis nocturnal windy PBL:nocturnal windy PBL: warm near-neutral, polluted warm near-neutral, polluted urban-plume urban-plume

vsvs. rural stable surface-inversion . rural stable surface-inversion

urban-plumeurban-plume

Clark & McElroy (1970):Clark & McElroy (1970):

rural inversionrural inversion

0FF

TTmin

TTmax

99

or NYC nocturnal UHI-or NYC nocturnal UHI-dome (Bornstein, 1968): dome (Bornstein, 1968):

in calm conditions orin calm conditions or along cross-wind direction during windy conditionsalong cross-wind direction during windy conditions

__________

uPBLuPBL

NN SS

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NYC NYC AVERAGEAVERAGE NOCTURNAL UHI (z): NOCTURNAL UHI (z): note note cross-over layercross-over layer (UHI < 0) aloft due to RFD, mixing, (UHI < 0) aloft due to RFD, mixing,

and/or sinking rural air, ??and/or sinking rural air, ??

Bars = ± σ

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AVERAGE MONTREAL NOCTURNAL UHI (z) AVERAGE MONTREAL NOCTURNAL UHI (z) AS A FUNCTION OF WIND SPEED: AS A FUNCTION OF WIND SPEED:

HISHIS LOOKING AT PROCESSES LOOKING AT PROCESSES (OKE AND EAST, 1971)(OKE AND EAST, 1971)

CROSS OVER (W/ SLOW SPEEDS)

NO CROSS-OVER (W/ FAST SPEEDS)

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HISHIS CLEAR CLEAR LINKAGELINKAGE OF SFC (left) & PBL (right) UHIs OF SFC (left) & PBL (right) UHIs

1313

HISHIS CLEAR SYNTHESES WITH THE WORK OF CLEAR SYNTHESES WITH THE WORK OF OTHERSOTHERS

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HISHIS CLEAR SYNTHESES OF UHI-EFFECTS ON CLEAR SYNTHESES OF UHI-EFFECTS ON OTHER URBAN PARAMETERS (more follows)OTHER URBAN PARAMETERS (more follows)

TT

SO2

θθ

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Urban-induced nocturnal elevated Urban-induced nocturnal elevated inversion-I trapsinversion-I traps home-heating emissions home-heating emissions Power plant plume is Power plant plume is trapped b/ttrapped b/t urban-induced inversions I & II urban-induced inversions I & II Inversion III is Inversion III is regional inversion regional inversion over-estimate of over-estimate of mixing depthmixing depth

Home-heatingSources

Plume

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NOCTURNAL UHI-INDUCED SFC-CONFLUENCE:NOCTURNAL UHI-INDUCED SFC-CONFLUENCE:otherwise-calm synoptic flow otherwise-calm synoptic flow

confluenceconfluence-center over urban center of Frankfurt, Germany-center over urban center of Frankfurt, Germany

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NYC TETROON-DERIVEDNYC TETROON-DERIVED w-VELOCITIES: w-VELOCITIES:Note Note (a) larger during unstable daytime-hours(a) larger during unstable daytime-hours(b) Smaller during more stable nighttime-hours (b) Smaller during more stable nighttime-hours (c) thin, weak nocturnal urban (c) thin, weak nocturnal urban elev-inversionelev-inversion layer-base stops w layer-base stops w

γγ

γγ(trapping)

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NYC inversion pattern several hrs after previous x-section:NYC inversion pattern several hrs after previous x-section:Note: Note: flow hit urban upwind edge flow hit urban upwind edge roughness-deceleration roughness-deceleration

up-motion up-motion inversion raised inversion raised

V V

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NYC URBAN EFFECTS ON NYC URBAN EFFECTS ON ρρv (g/cm (g/cm3):):

Large nightLarge night UHI, UHI, ρρvv-island, & RH-deficit-island, & RH-deficit

DayDay

NiteNite

2020

URBAN IMPACTS ON PRECIPURBAN IMPACTS ON PRECIP

• INITATIONINITATION BY THERMODYNAMICS (at SJSU) BY THERMODYNAMICS (at SJSU)– LIFTINGLIFTING FROM FROM

•UHIUHI CONVERGENCE CONVERGENCE

•THERMALTHERMAL & MECHANICAL CONVECTION & MECHANICAL CONVECTION vs.vs.

– DIVERGENCEDIVERGENCE FROM FROM BUILDING BARRIER EFFECTBUILDING BARRIER EFFECT

• AEROSOL MICROPHYSICS AEROSOL MICROPHYSICS – SLOWER SLOWER SECONDARYSECONDARY DOWNWIND ROLE DOWNWIND ROLE – METROMEX & PROF. D. ROSENFELD (HUJI)METROMEX & PROF. D. ROSENFELD (HUJI)

2121

NYC splitting thunderstorm (via precip radar-NYC splitting thunderstorm (via precip radar-echoes)echoes)

Should be due to dynamics & aerosols?Should be due to dynamics & aerosols?

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ATLAN UHI-INITIATED STORM: OBS GOES-SATELLITE & PRECIP (UPPER) & MM5 w’s & precip (LOWER)

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Fluid-dynamicsFluid-dynamics meso-scale PBL-UHI meso-scale PBL-UHI work of work of J. Hunt (part 1)J. Hunt (part 1)

• UsesUses – Linearized Navier-Stokes equationsLinearized Navier-Stokes equations– Scale argumentsScale arguments– Froude No. scalingFroude No. scaling– Analytical solutions Analytical solutions

• Compares effects ofCompares effects of– Roughness-change Roughness-change – Coriolis turning Coriolis turning – UHI UHI magnitudemagnitude– Building heightsBuilding heights– City sizeCity size– Time of dayTime of day

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Fluid-dynamicsFluid-dynamics meso-scale PBL UHI- meso-scale PBL UHI-work of work of J. Hunt (part 2)J. Hunt (part 2)

• Urban-climate parameters studiedUrban-climate parameters studied– Mixing-depth variationMixing-depth variation– Mean velocity fieldsMean velocity fields– Thermal & mechanical turbulenceThermal & mechanical turbulence– Precipitation distributionPrecipitation distribution

• Goals: Goals: – SynthesisSynthesis of three sources of information (PBL of three sources of information (PBL

obs, fluid dynamic scale arguments, & meso-met obs, fluid dynamic scale arguments, & meso-met models)models)

– Two papers:Two papers: Weather (qualitative) & QJRMS Weather (qualitative) & QJRMS (quantitative)(quantitative)

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Some important outstanding science Some important outstanding science

questionsquestions • What is the cause of UHI What is the cause of UHI cross-overcross-over effect effect• What are the effects of radiative flux divergence from What are the effects of radiative flux divergence from

black carbonblack carbon aerosols on the thermal structure of the aerosols on the thermal structure of the uPBLuPBL

• What are the relative roles of UHI and barrier dynamics What are the relative roles of UHI and barrier dynamics versus urban aerosols on versus urban aerosols on urban precipurban precip patterns patterns

• What fraction of PBL flow goes around, over, and through What fraction of PBL flow goes around, over, and through the city as a function of stabilitythe city as a function of stability

• How can How can PBL obsPBL obs be made in urban areas be made in urban areas• How can research How can research meso-met modelsmeso-met models be better urbanized be better urbanized• How can the How can the urban morphological dataurban morphological data needed as input needed as input

to urbanized meso-met models be obtained to urbanized meso-met models be obtained • How will urban climate effects in various climatic regions How will urban climate effects in various climatic regions

be impacted by a be impacted by a changing global climate changing global climate

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Questions?Questions?