Calculation%20of%20Urban%20Anthropogenic%20Heat%20Flux

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Numerical simulations of boundary layer
structure during the high pollution episode in
Tehran region
Hossein Malakooti, Bruno Sportisse, Luc Musson
Genon
Air Quality Control Company (AQCC)
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Motivation of the study Study of urban climate
alteration in PBL structure and meteorological
fields in Tehran region. Interaction between UHI
circulation and mountain flows.

• Challenges
• MM Models not designed to capture change in urban
  climate and at low resolution fail to capture
  heat island mitigation.
• Land use/land cover and physical properties of
  material and surfaces becomes new critical issue
  on urban.
• Anthropogenic heat fluxes form human activity.
• How, in various situations, urbanization
  interacts with other local forcing factors .

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Topographic flows (mountain and valley winds)
Following the convention of Segal and Arritt
(1992) nonclassical mesoscale circulations
(NCMCs) can be generated by differential sensible
and latent heat fluxes to the atmosphere produced
by spatial gradients thermal and radiative
properties such as albedo, thermal conductivity,
differences in snow cover or vegetation (Segal et
al. 1989 Segal et al. 1991 Rife et al. 2002,)
In valley cities and during calm periods,
condition may be lead to critical air quality
problem due to low horizontal ventilations
especially in transition between slope flows in
early morning and in the late afternoon (Whiteman
1990, 2000) and also due to combining of slop
winds with urban heat island, especially during
winter and night time, when vertical diffusion is
small (Atkinson, 1981).
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Urban Heat island

• What is causing
• Canyon effects (blocking of radiation, and wind)
• Anthropogenic heating (heat generation by human
  activity)
• Longwave re-emission from the warmer air above
  the city (local greenhouse effect and induced
  vertical warm advection)
• Changes in the thermal properties of materials
  (thermal storage)
• Lack of evapotranspiration (lack of vegetation
  and standing water) ( Oke, 1998b).

Aerodynamic contrasts can lead to enhanced or
suppressed mechanical mixing and therefore affect
vertical and horizontal diffusion and transport
(Grimmond and Oke 1999).
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Local Meteorology

• Average altitude from MSL 1250 m (1100-1700
  meters above MSL)
• Location 51 E, 35 N
• Average of annual rainfall 230 mm/year

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Synoptic condition during 4 6 th December 2005
500 mb chart
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Sodar observation
5 December 2005
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DA-SM2-U urban canopy representation
Surface types for DA-SM2-U Surface types for DA-SM2-U Surface types for DA-SM2-U Surface types for DA-SM2-U
nat bare soil located between the sparse vegetation elements pav Paved surface located between the sparse vegetation elements
bare Bare soil without vegetation cova Paved surface located under the vegetation
vegan Vegetation over the bare soil bui Building roofs
vega Vegetation over paved surface wat Water surface
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DA-SM2-U urban canopy representation
j index for surface type k level above the
ground Surfj (k) top area density of the
surface type j at the level k (m2 m-2) fj
horizontal surface density of the surface type j
(m2m-2) Afj (k) and Apj (k) frontal area
density (m2 m-3) and plan area density (m2 m-3)
respectively
horizontal air density at the level k
total top area density at the level k
volume air density (m3 m-2) at the level k,
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• DA-SM2-U modifications have been implemented
  inside two main parts
• MM5 GSPBL scheme by modifying of conservation
  equations and turbulence length.
• Soil model SM2-U by modifying surface canopy heat
  fluxes equations and ground part equations.

GSPBL scheme modifications
A Momentum equation
Source due to the presence of horizontal surface
Pressure and viscous drag force by vertical
surfaces
Cdbui 0.4, Cdvegn Cdvega 0.2.
B Thermal equation
sensible heat from roofs vegetation
anthropogenic heat flux
C Humidity equation
humidity flux
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D Turbulent kinetic energy equation
shear production by building horizontal surfaces
buoyancy production by building and vegetation
sensible heat fluxes anthropogenic heat fluxes
wake production of TKE due to interaction between
mean flow and canopy elements
TKE dissipation by canopy elements
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E Turbulent length scale (TLS)
The mixing length lBL is derived from the upward
and downward displacements (lup and ldown) that
could be achieved by parcels having kinetic
energy equal to the mean TKE before being stopped
by buoyancy effects.
Bougeault and Lacarrère (1989)
and
Bélair et al. (1999)
above the canopy, l lBL
Martilli et al. (2002),
for
for
.
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Description of the SM2-U(3D) Model
Masson (2000) Brown (2000) Dupont (2001)
Mean heat flux inside the canopy
Net radiation flux
Consideration exponentially decay toward the
ground ( kex 1.5 the radiation extinction
coefficient )
Latent heat flux from paved surfaces
The latent heat flux is considered as emitted at
the floor level, thus,
where Surfpav is the top area density of the
street canyon.
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Sensible and net rediation flux from paved
surfaces
The sensible and net radiative fluxes assessed at
the top of the street canyons are distributed
inside the street following the sky view factor
at the ground level is
To account for a vertical distribution of street
canyons, the contributions at the level k of the
higher street canyons having their tops between
the levels k 1 and ktop are considered by
it is assumed that (i) all buildings are
parallelepipeds with the same square horizontal
section characterized by their area Sbui, (ii)
surrounded by paved surfaces, and (iii) each
street canyon has a constant width with the
height.
The calculations of the sky view factors are
adapted from Masson (2000)
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winter and summer workday city-scale
anthropogenic heat flux profiles
Daily average workdays patterns released near
surface in winter and summer
The diurnal profiles have morning and evening
peaks, with summertime and wintertime maxima up
to 44Wm2 and 65Wm2 respectively. The foul
consumption component is the main one in winter
with a 54 share and traffic with 44 in summer.
Based on our distribution analysis with 500 meter
resolution of Tehran region we find that the
urban core region may have anthropogenic heating
values 4-7 times the magnitudes of the city-scale
values presented in this paper, especially in
morning and evening and with higher spatial
resolution, it is observed values more than this
too.
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Model application
One-way nested configuration for several days in
December including five nested computational
domains with 81., 27., 9., 3., and 1. km
horizontal grid spacing. DA-SM2-U is used only on
the 1. km domain. To compare DA-SM2-U (Qf and
non Qf) with RA MM5 versions, one other
simulation using RA is performed a standard
version of MM5 (RA-SLAB).
The first four domains are run with 40 vertical
sigma layers. The 1. km domain includes 130 -
130 grid points and 60 vertical sigma layers
covering the Tehran metropolitan area. 10 urban
Sub-categories for land use FDDA is used on the
first three domains (Stauffer and Seaman ,1994).
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Analyses of the Vertical Profiles inside the RSL
and PBL
At 2 pm
At 4 am
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Friction velocity TKE
At 2 pm
At 4 am
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Wind field at 4 pm at 25 m AGL December
5th 2005 RA-SLAB
Wind field at 4 pm at 25 m AGL December 5th
2005 DA-SM2-U Qf off
Wind field at 4 pm at 25 m AGL December 5th
2005 DA-SM2-U Qf on
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Temperature field at 4 pm at 2 m AGL December
5th 2005 RA-SLAB
Temperature field at 4 pm at 2 m AGL December
5th 2005 DA-SM2-U Qf off
Temperature field at 4 pm at 2 m AGL December
5th 2005DA-SM2-U Qf on
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Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005 DA-SM2-U Qf off
Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005 RA-SLAB
Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005DA-SM2-U Qf on
10-6m2s-1Kkg-1 1 PVU
at 4 pm
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Wind field at 4 am at 25 m AGL December
5th 2005 RA-SLAB
Wind field at 4 am at 25 m AGL December 5th
2005 DA-SM2-U Qf off
Wind field at 4 am at 25 m AGL December 5th
2005 DA-SM2-U Qf on
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Temperature field at 4 am at 2 m AGL December
5th 2005 RA-SLAB
Temperature field at 4 am at 2 m AGL December
5th 2005 DA-SM2-U Qf off
Temperature field at 4 am at 2 m AGL December
5th 2005DA-SM2-U Qf on
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Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005 RA-SLAB
Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005 DA-SM2-U Qf off
Circulation Pot. Tem. Distribution across BB,
Dec 5th 2005DA-SM2-U Qf on
4 am
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Comparison between observation and simulations
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• Conclusions
• Tehran PBl structure is extremely under effect
  of topographic and heat island flows and
  circulations and their interaction and show a
  multi layer structure.
• The roughness approach (RA) are unsatisfactory at
  neighbourhood scales in this area.
• Urban Roughness-Induced Convergence and UHI
  Thermal Circulation.
• within the canopies, the DA-SM2-U meteorological
  fields seem well simulated following the canopy
  morphology decrease of the wind speed inside the
  dense canopies, skirting of the flow around the
  canopy blocks, warmer air inside the vegetation
  canopy than above open areas during the night and
  conversely during the day, and constantly warmer
  air inside the urban canopy .
• A discontinuity in the eddy diffusivity is
  simulated by DA-SM2-U between the canopies and
  the upper atmosphere, with small values of the
  eddy diffusivity inside the canopies, inducing a
  limitation of the turbulent exchanges between the
  inside and the outside of the canopies.
• UHI Displacement/De-stabalized Boundary Layer.
• The vertical profiles of the potential air
  temperature in urban areas have shown that
  simulations using SM2-U reduce the tendency
  toward stable stratification. They even yield a
  neutral layer during the night because of the
  anthropogenic heat fluxes and also the heat
  released by urban surfaces.
• These results indicate that using a UCP may have
  significant ramifications for air-quality
  modeling at this scale because the dynamical
  characteristics of the volume in which pollutants
  are injected has been altered.

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Thank you for listening