Effects of Land Cover Modifications in MM5 on Surface Energetics in Phoenix

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Effects of Land Cover Modifications in MM5 on
Surface Energetics in Phoenix

• Susanne Grossman-Clarke, Joseph. A. Zehnder,
• William L. Stefanov,
• Harindra J.S. Fernando, Sang-Mi Lee
• Environmental Fluid Dynamics Program
• Arizona State University

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Introduction

• Focus on Phoenix
• Central-Arizona Phoenix (CAP)
• Long-Term Ecological Research (LTER) Project.
• Mesoscale Meteorological Modeling Group
• Neighborhood scale distributions of near-surface
• meteorological variables.

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Introduction - Applications

• Urban heat island
• Water use (evaporation transpiration)
• CO2 dome
• Air quality
• Urban design
• Biogeochemical cycles

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Introduction Characteristics of Phoenix

• Fastest growing city in the US.
• Mostly suburban core, surrounded by irrigated
  agricultural land and dry sparsely vegetated
  desert, embedded in complex terrain.
• Irrigated vegetation in suburban neighborhoods is
  important for urban energy balance.

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Introduction - Land Surface Representation in MM5

• Land use and soil data
• Land use and soil classes
• Physical and biological parameters
• Physical approach for describing energy, momentum
  and matter exchange between land surfaces and the
  atmosphere.

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Land Use Data Preparation

• Land cover data 30 meter resolution
• Based on 1998 Landsat Thematic Mapper satellite
  images for Phoenix (visible and shortwave
  infrared vegetation index).
• Postclassification using additional data sets in
  expert system.

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Land Use Data 1998
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Land Use Data Preparation

• Reprojecting land use data according to the grid
  information of USGS 30-second data in GIS.
• Zonal summing of the 30 m data set within 30
  second grid cells.

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Land Use Data Preparation

• Three urban classes in 25-category USGS land
  cover classification
• Built-up urban, mesic and xeric residential.
• Composition of mesic and xeric residential areas
  in terms of typical fractions of irrigated and
  total vegetation.
• MM5 water availabilty factor.

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Surface Parameters

• Albedo
• Roughness length
• Moisture availability
• Emissivity
• Heat storage capacity

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Land Use Class Characteristics (LTER - 200 point
survey)
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1km x 1km Land Use 1998 Satellite Data
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2km x 2km Land Use 1998 Satellite Data
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2km x 2km Land Use 1976 USGS Data
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MM5 (a) 1976 USGS (b) 1998 Land Use Data
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Design of Numerical Simulation

• 1700 LST May 28 1700 LST May 30, 2001
• Spatial dimension
• Nested Run of MM5 54 Km ? 18 Km ? 6 Km ? 2 Km
• 32 vertical layers
• Meteorological data
• Initial Boundary conditions NCEP Eta
  Analysis 40 km
• Elevation and land use data resolution 30 sec.
• MRF boundary layer scheme 5 layer soil model.

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Surface Energy Balance Equation
Tg Ground temperature K Cg Heat capacity
of the ground J m-2 K-1 Rn Net radiation
balance W m-2 H Sensible heat flux W
m-2 G Soil heat flux W m-2 lE Latent heat
flux W m-2
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Latent Heat Flux
M Moisture availability factor
- z0 Roughness length m Yh Stability
function - qvs Saturation specific humidity
- qva Specific humidity at za-
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Sensible Heat Flux
Ta Air temperature at za K u Friction
velocity m s-1 L Monin Obukhov length
m k von Karman constant - cp Specific
heat capacity of air J K-1 kg-1
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Boundary Layer Height
h Boundary layer height Ribcr Critical bulk
Richardson number (0.5) Qva Virtual potential
temperature at za Qv Virtual potential
temperature at zh Qs Virtual potential
temperature at ground level z0 U(h) Wind speed
at zh
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Simulated Ground Temperatures (a) USGS (b) 1998
Land Use Data
29 May 2001 1400 LST
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Differences in Ground Temperatures
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Simulated Latent Heat Fluxes (a) USGS and (b)
1998 Land Use Data
29 May 2001 1400 LST
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Differences in Latent Heat Fluxes
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Simulated Sensible Heat Fluxes (a) USGS (b) 1998
Land Use Data
29 May 2001 1400 LST
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Differences in Sensible Heat Fluxes
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Simulated 2m Air Temperatures(a) USGS (b) 1998
Land Use Data
29 May 2001 1400 LST
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Differences in 2m Air Temperatures
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Simulated Boundary Layer Heights (a) USGS (b)
1998 Land Use Data
29 May 2001 1400 LST
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Differences in Boundary Layer Heights
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Results
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Results
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Results
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Results
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Results
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Results
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Results
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Summary
Urban land use is likely to have a significant
impact on the simulated near surface temperatures
and PBL heights in MM5. Model validation is
necessary.
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Summary

• Problems
• Physical representation of urban surfaces in MM5.
• Slope flows in complex terrain (timing,
  strength), eddy diffusivities.

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Nitrogen Dry Deposition Modeling

• Assess indirect and direct effects of urban
  vegetation on nitrogen dry deposition in the CAP
  LTER study area, including Phoenix metropolitan
  area.
• Is N deposition significant input to N mass
  balance of the area.
• Changes in biogeochemical cycles.
• Effects on ecosystems.

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Nitrogen Dry Deposition Modeling

• Models-3/CMAQ Problems
• Physical approach of describing matter transport
  in urban roughness sub-layer.
• Land use data.
• Diagnostic model
• Make use of long-term measured pollutant
  concentrations and weather variables
• Investigate seasonal changes of dry nitrogen
  deposition.

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Nitrogen Dry Deposition Modeling

• Assess indirect and direct effects of urban
  vegetation on nitrogen dry deposition in the CAP
  LTER study area, including Phoenix metropolitan
  area.
• Is N deposition significant input to N mass
  balance of the area.
• Changes in biogeochemical cycles.
• Effects on ecosystems.

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Vertical Dry Deposition Flux
z0 Sink height at the surface zr Reference height
in the atmosphere C(zr) Pollutant concentration
at reference height C(z0) Pollutant concentration
at the surface vd Deposition velocity ?a Air
density
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Deposition Velocity
ra Aerodynamic resistance rb Boundary layer
resistance rs Surface resistance
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Aerodynamic resistance
L Monin-Obukhov length k von Karman constant u
Friction velocity ?h Similarity function for
heat (Holtslag van Ulden, 1983 and Dyer
Hicks,1970)
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Monin-Obukhov Length
H Sensible heat flux k von Karman constant u
Friction velocity Ta Air temperature
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Sensible Heat Flux
Rn Net radiation G Soil heat flux A Anthropogenic
heat production a Water availability factor
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Water Availability Factor
fi Fraction of irrigated vegetation cover (Oke,
2001)
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Canopy Resistance
rmin Minimum canopy resistance Rs Incoming solar
radiation T Air temperature Tmin Cold limit (5
0 ?C) Tmax Heat limit (45 - 50 ?C) To Optimum
temperature (30 ?C)
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Air quality monitoring station Phoenix Supersite.
NO2 dry deposition flux (FNO2 ) and measured NO2
concentrations (CNO2 --- )
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Nitrogen Dry Deposition Modeling
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Nitrogen Dry Deposition Modeling
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Modeling Nitrogen Dry Deposition
Spatial distribution of total nitrogen dry
deposition flux 1998