Environment Canada, Meteorological Service of Canada, Meteorological Research Branch

1. CRTI Project # 02-0093RD 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. 15-km GEM Regional GEM-LAM 250 m GEM-LAM 1 km OKC GEM-LAM 2.5 km Numerical Set-up

3. 15-km GEM Regional GEM-LAM 250 m GEM-LAM 1 km OKC GEM-LAM 2.5 km 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)

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. zbld 2 Tcanyon zbld TPWIDS 8 m 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 zbld=60 m

10. ANL CBD PNNL Urban-scale evaluation Daytime IOP6 • 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. B A 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. ANL CBD PNNL Urban-scale evaluation Nighttime IOP9 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. B A 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. Urban canopy Vegetated canopy TEB ISBA Air Temperature Diagnostic Atmospheric model zatm • 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)