HIGHLIGHTS AND CHALLENGES OF URBAN MET MODELING

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HIGHLIGHTS AND CHALLENGES OF URBAN MET MODELING

• R. BORNSTEIN (SJSU)
• K. CRAIG (PSU)
• A. MARTILLI (UBC)
• S. DUPONT (FMS)
• 2004 AMS

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OUTLINE

• WHY URBAN AREAS (Walt Dabberdt)
• CURRENT STATUS
• URBAN WEATHER/CLIMATE
• MESOMODELS
• MODEL URBANIZATION
• PROBLEM AREAS
• MESOMODELS
• MODELURBANIZATION
• OUTLOOK FOR FORECASTING

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NEW URBAN CLIMATE CAUSES

• GRASS/SOIL ? CONCRETE/BUILDINGS ?
• NEW THERMAL INERTIA ?
• ALTERED SFC HEAT MOSITURE FLUXES
• FUEL CONSUMPTION ?
• ATM POLLUTION, HEAT, AND MOISTURE
• BUILDINGS ATM POLLUTION?
• ALTERED SOLAR IR RADIATIVE FLUXES

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URBAN WX ELEMENTS

• TEMP PRECIP increased decreased
• VISIBILTITY decreased
• WIND DIRECTION con- divergence
• TURBULENCE mechanical and thermal
• PBL NIGHT STABILITY neutral
• FRONTS slowed
• THUNDERSTORMS triggered or split

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HUMAN-HEALTH IMPACTS OF URBAN CLIMATE

• UHI ? THERMAL STRESS
• PRECIP ENHANCEMENT ? FLOODS
• TRANSPORT DIFF PATERNS FOR
• POLLUTION EPISODES
• EMERGENCY RESPONSE

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URBAN ATM MODELING MULTISCALE PROBLEM

• MODELING SCALES
• Canyon microscale (CFD, LES, or analytic) models
• Urban BL mesoscale (numerical) models
• LINKAGE PROBLEMS
• LOWER LIMIT OF HORIZ GRID IN REYNOLDS-AVERAGED
  MESOMODELS about 1 km
• LES CFD MODELS REQUIRE CPU and time
• LES/CFD LINKAGE WITH MESOMODELS
• hard BCs (subject of Sat. workshop)

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MESOMODEL PROBLEM AREAS

• LARGE SCALE FORCING
• MIN HORIZ-GRID SIZE
• SUB-GRID TURBULENCE CLOSURE
• SFC CHARACTERISTICS/BCs

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URBAN MESOMODEL PROBLEMS

• BUILDING-HEIGHT VARIATION ?
• where is lower boundary?
• INHOMOGENEOUS SFC TYPE ?
• thermal, rad, and roughness param are f(x,y)
• Roughness sub-layer u(z) vs. SBL
• AEROSOLS ? RAD FLUX DIV ?
• interactive met and air quality models ?
• elev urban inversions actinic flux

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LOWER MODELBOUNDARY SURFACE?

• GROUND SURFACE
• COMBO OF GROUND, WALL, AND ROOF SURFACES
• ROUGHNESS HEIGHT
• ROUGHNESS-SUBLAYER TOP (SAME AS SBL BASE)
  

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MESO-MODEL URBANIZATION

• SIMPLE (NON-POROUS FLOWS)
• no T V within URBAN CANYONS
• Look up tables for land use classes
• Taha (1998) OHM model for heat storage term
• Bornstein (1993) building-barrier effects
• COMPLEX (POROUS FLOWS) from
• Yamada (1982) forest canopy formulation
• Brown Williams (1998) roof-drag momentum
• Mason (2000) urban canyon-energy effects
• Martilli (2002) effects on heat, momentum, TKE
• Dupont (2004) Martilli forests GIS data

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Subgrid VariabilitySimple (look-up table)

• A. Predominant param
• B. Average param (Kimura 1991)

WATER 20
GRASS 30
CONCRETE 50
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Look-up table (continued)

• INDIVIDUAL PARAM ?
• INDIVIDUAL FLUXES ?
• AVERAGE FLUX ? ONE TEMP
• ADVANCED TECHNIQUES
• GIS VALUES AS f(x,y)
• URBAN CANYON MODULES

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From Masson (2000)
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From Masson (2000)
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Modification of Momentum Equations

• Drag term added to horizontal momentum equations
• furban fraction of surface grid cell covered by
  urban land use
• a(z) urban canopy area profile
• Cd drag coefficient
• Winds modeled at height within urban canopy (but
  with no buildings)

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Modification for q2

• Additional Mixing Length Scale
• based on size of urban roughness elements that
  induce canyon circulations
• a) Sievers (2001)
• b) Martilli et al. (2000)

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MESOMODEL RESULTS

• URBMET/TVM
• NYC
• SEA BREEZE FRONTS
• MM5
• ATLANTA
• URBAN-INITIATED THUNDERSTORMS

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Rough, warm urban simulation
Rough, warm urban simulation
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NYC LESSIONS

• MUST INCLUDE ALL IMPORTANT URBAN EFFECTS
• OBS SHOW YOU WHAT TO EXPECT AND MODEL SHOWS YOU
  STRUCTURE IN AREAS W/O OBS

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MM5 23 m T on 26 July 1500 UTC
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MM5 23 m V (barb 1m/s) for 26 July 1700 UTC
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MM5 23 m Divergence (contour 1.0e-4 1/s) for 26
July 1500 UTC
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E-W section of potential T (0.5 K) and div
(solid)/con (dashed) (contour interval 5 e 5
1/s) through max UHI-induced con region 26 July
1500 UTC. Thick horiz line denotes urban area.
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MM5 section of potential T and w through
strongest UHI-induced updraft at 1700 UTC. Max w
is 4.3 m/s.
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MM5 Cumulative Precipitation (mm) through 26 July
0100 UTC
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MM5 23 m T on 26 July 1500 UTC NO-URBAN
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MM5 Cumulative Precip (mm) through 26 July 0100
UTC for NO-URBAN Case.
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EMERGENCY RESPONSE

• CFD URBAN NEIGHBORHOOD
• CANYON SCALE
• LINK WITH INDOOR
• SUBWAY

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Required Future Research (Dabberdt et al. 2000)

• Urban Field Studies, e. g,
• URBAN 2000, JOINT URBAN, BUBBLE, UAO
• Wind-tunnel, fluid, LES, and CFD models?
• improved canyon parameterizations
• Non-M-O parameterizations to replace M-O
• More GIS inputs
• Links b/t CFD/LES and meso-models (Mestayer and
  Bornstein 1999)

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REAL-TIME URBAN FORECASTS REQUIRE

• GOOD LARGE-SCALE WX-MODEL INPUT
• GOOD URBAN-CANYON MODULES IN MESO-MODELS
• FAST CPU
• GOOD MESOSCALE (SFC UPPER AIR) OBS NETWORKS
  (INCLUDING COMMUNICATIONS)