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

Prof. Robert Bornstein Dept. of Meteorology, San Jose State University San Jose, CA, USA, pblmodel@hotmail.com Prof. Julian Hunt University College, London, UK Presented at the T. R. Oke Symposium AMS Annual Meeting, Phoenix AZ Jan 2009 Funding source: NSF.

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

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  1. Prof. Robert Bornstein Dept. of Meteorology, San Jose State University San Jose, CA, USA, pblmodel@hotmail.com Prof. Julian Hunt University College, London, UK Presented at the T. R. Oke Symposium AMS Annual Meeting, Phoenix AZ Jan 2009 Funding source: NSF Tim Oke and the extension-upwards of UHI-observations into the PBL

  2. OVERVIEW • URBAN CLIMATE ELEMENTS: a review • TIM OKE’S (and his group) PBL-UHI work • Observations • Explanations • Impacts on other urban-PBL climate elements • Synthesis of ideas from • PBL observations (Oke and his group) • Analytical fluid dynamics (work of Prof. Hunt) • Urbanized meso-met models (Bornstein & many other groups)

  3. uPBL CLIMATE ELEMENTS:battles between conflicting effects Monatomic effects • VISIBILTITY: decreased • TURBULENCE: increased (mechanical & thermal) • PBL NIGHT STABILITY: neutral • FRONTS (synoptic & sea breeze): slowed More complex effects • TEMP: increased (UHI) or decreased • MOISTURE: increased or decreased • WIND SPEED (V): increased or decreased • WIND DIRECTION:convergence or divergence • PRECIP: increased or decreased • THUNDERSTORMS: triggered or split

  4. PBL scales & layers (modified after Oke, 1997) UBL RSL RSL UCL UCL

  5. uPBL sub-layers • Urban mixing layer • Non-homogeneous • Non-stationary • Urban SfcBL: has several sub-layers (next slide) • Urban surface: where is it in urban meso-met models: • ground • roughness length, zo • rooftop • displacement height, d • top of roughness sub-layer (RSL) • Urban sub-surface:consists of • ground • walls • roofs

  6. Integration of all surface temperatures gives ‘the’ SUHI “Surface” temperatures and ‘the’ Sfc UHI (SUHI): from Oke 2008

  7. uSfcBL sub-layers • Urban Canopy Layer (UCL) • Between buildings (extends from 0-h) • Flow pattern is f (W/h ratio)  skimming, vortex, or isolated-obstacle flow • Roughness sub-layer, RSL • Flux-blending layer (extends from h to 3h) • M-O theory not valid, as u*(z) • Inertial sub-layer (Oke’s tower obs) • Fluxes have blended (>3h) • M-O theory is valid, asu* not f(z)

  8. St. Louis nocturnal windy PBL: warm near-neutral, polluted urban-plume vs. rural stable surface-inversion 0F Tmin Tmax urban-plume rural inversion Clark & McElroy (1970):

  9. or NYC nocturnal UHI-dome (Bornstein, 1968): • in calm conditions or • along cross-wind direction during windy conditions uPBL S N _____

  10. NYC AVERAGE NOCTURNAL UHI (z): note cross-over layer (UHI < 0) aloft due to RFD, mixing, and/or sinking rural air, ?? Bars = ± σ

  11. AVERAGE MONTREAL NOCTURNAL UHI (z) AS A FUNCTION OF WIND SPEED: HIS LOOKING AT PROCESSES (OKE AND EAST, 1971) • CROSS OVER (W/ SLOW SPEEDS) NO CROSS-OVER  • (W/ FAST SPEEDS)

  12. HIS CLEAR LINKAGE OF SFC (left) & PBL (right) UHIs

  13. HIS CLEAR SYNTHESES WITH THE WORK OF OTHERS

  14. HIS CLEAR SYNTHESES OF UHI-EFFECTS ON OTHER URBAN PARAMETERS (more follows) T SO2 θ

  15. Urban-induced nocturnal elevated inversion-I traps home-heating emissions • Power plant plume is trapped b/t urban-induced inversions I & II • Inversion III is regional inversion  over-estimate of mixing depth Plume Home-heating Sources

  16. NOCTURNAL UHI-INDUCED SFC-CONFLUENCE: otherwise-calm synoptic flow  confluence-center over urban center of Frankfurt, Germany

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

  18. NYC inversion pattern several hrs after previous x-section: Note: flow hit urban upwind edge  roughness-deceleration  up-motion  inversion raised V 

  19. NYC URBAN EFFECTS ON ρv (g/cm3): Large night UHI, ρv-island, & RH-deficit Day Nite

  20. URBAN IMPACTS ON PRECIP • INITATION BY THERMODYNAMICS (at SJSU) • LIFTING FROM • UHI CONVERGENCE • THERMAL & MECHANICAL CONVECTION vs. • DIVERGENCE FROM BUILDING BARRIER EFFECT • AEROSOL MICROPHYSICS • SLOWER SECONDARY DOWNWIND ROLE • METROMEX & PROF. D. ROSENFELD (HUJI)

  21. NYC splitting thunderstorm (via precip radar-echoes) Should be due to dynamics & aerosols?

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

  23. Fluid-dynamics meso-scale PBL-UHI work of J. Hunt (part 1) • Uses • Linearized Navier-Stokes equations • Scale arguments • Froude No. scaling • Analytical solutions • Compares effects of • Roughness-change • Coriolis turning • UHI magnitude • Building heights • City size • Time of day

  24. Fluid-dynamics meso-scale PBL UHI-work of J. Hunt (part 2) • Urban-climate parameters studied • Mixing-depth variation • Mean velocity fields • Thermal & mechanical turbulence • Precipitation distribution • Goals: • Synthesis of three sources of information (PBL obs, fluid dynamic scale arguments, & meso-met models) • Two papers: Weather (qualitative) & QJRMS (quantitative)

  25. Some important outstanding science questions • What is the cause of UHI cross-over effect • What are the effects of radiative flux divergence from black carbon aerosols on the thermal structure of the uPBL • What are the relative roles of UHI and barrier dynamics versus urban aerosols on urban precip patterns • What fraction of PBL flow goes around, over, and through the city as a function of stability • How can PBL obs be made in urban areas • How can research meso-met models be better urbanized • How can the urban morphological data needed as input to urbanized meso-met models be obtained • How will urban climate effects in various climatic regions be impacted by a changing global climate

  26. Questions?

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