Urbanization affects on meteorology

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Urbanization affects on meteorology

• Chris Loughner

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Outline

• Background
• Objectives
• Method
• Results
• Urban heat island
• Urban heat island and bay breeze
• Conclusion

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What is the urban heat island (UHI)?

• The net effect of replacing natural vegetation
  with dry impervious surfaces such as buildings
  and roads. This alters the exchange of energy
  and moisture between the surface and atmosphere
  and may modify the meteorology of the local
  climate (Jin et al. 2005).
• Manley (1958) was the first to use the term
  urban heat island
• Urban heat islands can affect the meteorology and
  air quality.
• Change radiation budget / temperature
• Change in hydrologic cycle (precipitation, latent
  heat exchange)
• Change wind / surface convergence
• Change pollution emissions
• Change atmospheric dispersion

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Recent Research

• Gallo et. al. (1992) used the AVHRR instrument to
  observe the UHI in several cities throughout
  North America by comparing the temperature in the
  cities with their adjacent rural regions.
• Jin et. al. (2005) used MODIS observations to
  determine
• the albedo in urban areas is lower than broadleaf
  deciduous forests
• the emissivity in urban areas is lower than
  cropland
• Shepherd and Burian (2003) used TRMM and ground
  based rain gauges to determine
• the UHI is more effective of producing more
  precipitation downwind of Houston during the warm
  season
• the UHI enhanced the convergence zone of the sea
  breeze causing more precipitation to fall
• Civerolo et. al. (1999) performed a modeling
  study to determine that air quality is dependent
  on surface characteristics

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Objectives

• Investigate the UHI for a summertime case under
  high pressure in the Baltimore, MD / Washington,
  DC metro area
• Determine if the UHI exists
• Determine if the UHI causes changes to the wind
  circulation

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Method

• Perform MM5 simulations for 7 cases
• Base case
• Natural case
• Albedo case
• Soil moisture case
• Emissivity case
• Roughness length case
• Thermal inertia and heat capacity case

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MM5 Model

• 4km x 4km resolution
• 80 x 80 grids
• Initial and boundary conditions NCAR NCEP
  Reanalysis data
• Dates 0000 UTC August 3, 2006 0000 UTC
  August 9, 2006

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City Versus Broadleaf Deciduous Forest Input
Values from the USGS land use / land cover
classification obtained from the AVHRR instrument
(Anderson et. al., 1976)
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Base Case
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Natural Case
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Albedo Case
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Soil Moisture Case
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Emissivity Case
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Roughness Length Case
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Heat Capacity Case
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3pm EDT August 6, 2006
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Temperature differences (K)
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Winds
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Sea level pressure differences (mb)
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Boundary layer height differences (m)
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Divergence differences (1/s)
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Vertical velocity differences (m/s)
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3pm EDT August 7, 2006
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Temperature difference
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Sea level pressure difference
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Divergence difference
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Vertical velocity difference
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Conclusions

• The UHI exists in the Baltimore / Washington, DC
  metro area
• The UHI causes a circulation by increasing
  convergence over the warm air
• The UHI can amplify the convergence and
  circulation associated with a sea / bay breeze