effects of land cover modifications in mm5 on surface energetics in phoenix susanne grossman-clarke,...
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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 ProgramArizona State University
Introduction
Focus on PhoenixCentral-Arizona Phoenix (CAP)
Long-Term Ecological Research (LTER) Project.
Mesoscale Meteorological Modeling GroupNeighborhood scale distributions of near-
surface meteorological variables.
Introduction - Applications
Urban heat island
Water use (evaporation & transpiration)
CO2 dome
Air quality
Urban design
Biogeochemical cycles
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.
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.
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.
Land Use Data 1998
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.
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.
Surface Parameters
Albedo
Roughness length
Moisture availability
Emissivity
Heat storage capacity
LU class USGS class
1 Cultivated veget.
3 - Irrigated agric.
2 Cultivated grass 3 - Irrigated agric.
3 River gravels 19 - Bare soil
4 Compacted soil 19 - Bare soil
5 Vegetation 11 - Decid. forest
6 Com./Industrial 1 - Urban and built-up
7 Asphalt/concrete 1 - Urban and built-up
8 Undisturbed desert
8 - Shrub land
9 Compacted soil 19 - Bare soil
10 Mesic residential New
11 Xeric residential New
12 Water 16 – Water
Land Use Class Characteristics
(LTER - 200 point survey)
Irrigated vegetatio
n
Xeric vegetatio
n
Bare soil
Asphalt,
concrete
Mesic residenti
al
40 - 2 58
Xeric residenti
al
3 22 2 73
Build-up urban
0-18 - 0-3 79-100
Native desert
- 38 62 -
1km x 1km Land Use: 1998 Satellite Data
2km x 2km Land Use: 1998 Satellite Data
2km x 2km Land Use: 1976 USGS Data
MM5 (a) 1976 USGS (b) 1998 Land Use Data
Design of Numerical Simulation
1700 LST May 28 – 1700 LST May 30, 2001Spatial 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.
Surface Energy Balance Equation
)( gTfEGHnRtgT
gC
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]
E … Latent heat flux [W m-2]
Latent Heat Flux
)/(ln
)(
0Lz
z
z
qTqkuME
aha
vagvsa
M … Moisture availability factor [-]
z0 … Roughness length [m]
h … Stability function [-]
qvs … Saturation specific humidity [-]
qva … Specific humidity at za[-]
Sensible Heat Flux
)/(ln
)(
0Lz
z
z
TTkucH
aha
agpa
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]
Boundary Layer Height
])([
)( 2
sv
vacr hg
hURibh
h … Boundary layer height
Ribcr … Critical bulk Richardson number (0.5)
va … Virtual potential temperature at za
v … Virtual potential temperature at z=h
s … Virtual potential temperature at ground level z=0
U(h) … Wind speed at z=h
Simulated Ground Temperatures (a) USGS (b) 1998 Land Use Data
29 May 2001 14:00 LST
Differences in Ground Temperatures
Simulated Latent Heat Fluxes (a) USGS and (b) 1998 Land Use Data
29 May 2001 14:00 LST
Differences in Latent Heat Fluxes
Simulated Sensible Heat Fluxes (a) USGS (b) 1998 Land Use Data
29 May 2001 14:00 LST
Differences in Sensible Heat Fluxes
Simulated 2m Air Temperatures(a) USGS (b) 1998 Land Use Data
29 May 2001 14:00 LST
Differences in 2m Air Temperatures
Simulated Boundary Layer Heights (a) USGS (b) 1998 Land Use Data
29 May 2001 14:00 LST
Differences in Boundary Layer Heights
Results
Results
Results
Results
Results
Results
15
20
25
30
35
40
45
0 4 8 12 16 20 0 4
Time of day
Ob
serv
ed t
emp
erat
ure
[oC
]
Stat. 1
Stat. 2
Stat. 3
Stat. 4
Stat. 5
Stat. 6
Results
15
20
25
30
35
40
45
0 4 8 12 16 20 0 4
Time of day
Sim
ula
ted
tem
per
atu
re [
oC
]
Stat. 1
Stat. 2
Stat. 3
Stat. 4
Stat. 5
Stat. 6
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.
Summary
Problems
Physical representation of urban surfaces in MM5.
Slope flows in complex terrain (timing, strength), eddy diffusivities.
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.
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.
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.
Vertical Dry Deposition Flux
0zCrzCadvdF
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
Deposition Velocity
srbrardv
1
ra Aerodynamic resistance
rb Boundary layer resistance
rs Surface resistance
Aerodynamic resistance
ku
L
z
L
dz
z
dz
r
hh
rh
h
r
a
0
0
ln
L Monin-Obukhov length
k von Karman constant
u* Friction velocity
h Similarity function for heat (Holtslag & van Ulden, 1983 and Dyer & Hicks,1970)
Monin-Obukhov Length
kgH
TcuL apa
3
H Sensible heat flux
k von Karman constant
u* Friction velocity
Ta Air temperature
Sensible Heat Flux
GARS
SH n1
1
s
p
dq
dTcS
Rn Net radiation
G Soil heat flux
A Anthropogenic heat production
Water availability factor
Water Availability Factor
222.0610.0 if
fi Fraction of irrigated vegetation cover (Oke, 2001)
Canopy Resistance
minmax
0max
0max
max
min
min0
2
2001min
TT
TT
s TTTT
TTTT
Rrcr
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)
Air quality monitoring station Phoenix Supersite.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 50 100 150 200 250 300 350
Julian Day 1998
C(N
O2)
[p
pm
]
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
F(N
O2)
[kg
N h
a-1
d-1
]
NO2 dry deposition flux (FNO2 —) and measured NO2 concentrations (CNO2 --- )
Nitrogen Dry Deposition Modeling
Contribution of individual land cover types to the estimated
annual NOx dry deposition at Phoenix Supersite
0
10
20
30
40
50
urban irrigated veg. bare soil shrubs & xeric
% o
f to
tal
NO
x d
epo
site
d
Urban Irrig. Veg.
Bare soil
Xeric
Cover [%] 59 21 8 12
FNOX[%] 31 41 6 22
Nitrogen Dry Deposition Modeling
Modeling Nitrogen Dry Deposition
Spatial distribution of total nitrogen dry deposition flux 1998