1. Meso-scale Model's Results
CRTI Project # RD
Oklahoma City
Meso-scale Model's Results
A. Lemonsu,
S. Bélair, J. Mailhot, L. Tong
Environment Canada, Meteorological Service of Canada,
Meteorological Research Branch
Development Division

2. Numerical Set-up 15-km GEM Regional GEM-LAM 250 m GEM-LAM 1 km OKC
Model
version
Res.
Grid
Version
Integration
Daytime IOP6
Nighttime IOP9
TimeStep
GEM reg
operational
15 km
Reg.
GEM320
PHY42
July 16, 0000 UTC
48 hrs
July 26, 0000 UTC
36 hrs
450 s
GEM/LAM
2.5 km
201x201
GEM322
PHY44
July 16, 0600 UTC
42 hrs
July 26, 0600 UTC
30 hrs
60 s
1 km
July 16, 1200 UTC
July 26, 1200 UTC
24 hrs
30 s
GEM-LAM 250 m
OKC
GEM-LAM 1 km
GEM-LAM 2.5 km
15-km
GEM Regional

3. Numerical Set-up Sensitivity tests:
Simulation “urban”, including the Town Energy Balance (TEB) model and using a specific urban land-use land-cover classification
Simulation “no-urban”, replacing OKC by grassland (ISBA)
GEM-LAM 250 m
OKC
GEM-LAM 1 km
GEM-LAM 2.5 km
15-km
GEM Regional

4. Methodology of Evaluation
Regional-scale evaluation
Comparison between 2.5-km GEM/LAM outputs and operational observations in Oklahoma State:
Near-surface parameters: MESONET operational network
Upper-air profiles: operational soundings of Norman (South of OKC)
Urban-scale evaluation
Comparison between 1-km GEM/LAM outputs and Joint Urban 2003 database:
Urban micro-climate inside the streets: PWIDS, SPWIDS, PNNL networks
Urban boundary layer: Radars/sodars, and Soundings south and north of CBD

5. Regional-scale evaluation
Daytime IOP6
Nighttime IOP9

6. Regional-scale evaluation
Daytime IOP6
Altitude (m)

7. Regional-scale evaluation
Nighttime IOP9
Altitude (m)
Nocturnal
Low Level Jet

8. Urban-scale evaluation
Daytime IOP6
OKC
10 rural stations (MESONET)
13 urban stations (PWIDS)

9. Urban-scale evaluation
Daytime IOP6
Sensitivity of the urban model to the geometric parameters:
By increasing the building height, roads and walls absorb less solar radiation and air temperature inside the street-canyon decreases at daytime
zbld=60 m
Tcanyon
TPWIDS
zbld 2
8 m
zbld=60 m

10. Urban-scale evaluation
Daytime IOP6
PNNL
ANL
CBD
Not enough vertical resolution to capture the sharp inversion at the top of the well-mixed layer
Model soundings not clearly sensitive to the inclusion of TEB
Large impact of the meteorology

11. Urban effect on daytime IOP 6
Potential temperature at z=50 m – 1600 LST
urban
no urban
The daytime urban heat island is advected according to the mean flow

12. Urban effect on daytime IOP 6
Potential temperature at z=50 m – 1600 LST
urban
no urban
3250
2700
2150
Altitude (m AGL)
1600
1050
500 50 A
City B A B
The atmospheric boundary layer is slightly warmer, north-east of the city, in the urban simulation: development of an urban plume

13. Urban-scale evaluation
Nighttime IOP9
PNNL
ANL
CBD
Altitude (m)
Quasi-neutral boundary layer at night above the city
ABL warmer downwind of the city
Too strong inversion near the surface in the model

14. Urban effect on nighttime IOP 9
Potential temperature at z=50 m – 0200 LST
urban
no urban

15. Urban effect on nighttime IOP 9
Potential temperature at z=50 m – 0200 LST
urban
no urban
500
Altitude (m AGL) 50 A
City B A B
The vertical structure of the atmospheric boundary layer is influenced by the presence of the city

16. Conclusion
GEM, including TEB, simulates the urban microclimate of OKC’s downtown
At street level:  Positive urban heat island at night
 Negative urban heat island at daytime
Daytime IOP:
Good performance of the model
Weak impact of the cities on local dynamics
Local dynamics mostly driven by larger-scale dynamics and soil conditions around the city
Nighttime IOP:
Good performance of the model for near-surface temperature
Underestimation of the quasi-neutral boundary layer over the city
Larger effect of the city on the structure of the ABL

17. Air Temperature Diagnostic
Atmospheric model
zatm
Vegetated canopy
ISBA
Urban canopy
TEB
In mixed environment (including vegetation + built-up covers), the near-surface air temperature is diagnosed using:
2-m air temperature above vegetation, diagnosed from Ta and Ts (ISBA)
air temperature inside the street-canyon (TEB)