1. Mesoscale Modeling with a 3D Turbulence Scheme Jocelyn Mailhot and Yufei Zhu (Claude Pelletier) Environment Canada MSC / MRB 3 rd Annual Meeting on CRTI Urban Canyon Project – Dorval QC – 22-23 August 2006

2. Implementing 3D Turbulence Current 1D (vertical) turbulent diffusion scheme parametrizes effects of large eddies in PBL High-resolution models (< 1km) partly resolve large eddies Adjustments needed to avoid “double-counting” of diffusion processes Must also include XY contributions as grid resolution increases and move toward LES (quasi-isotropic 3D diffusion) Cascade to LES-type model resolution (Large-eddy simulation - i.e. 10-50m) with Smagorinsky-Lilly approach Smooth transition of diffusion intensity as function of model resolution

3. Implemented in MC2 Included all XY components of the dynamic Reynolds stress tensor Added TKE gradient terms Horizontal corrections introduced in all remaining transport equations Finite difference discretization on Arakawa-C grid and Charney-Phillips vertical staggering (this has yet to be done in GEM) Modified operator splitting technique used by TKE solver Modified appropriate scale- dependent mixing length Implementing 3D Turbulence

4. Ratio of H/V motion components (OKC 16:00 CDT, 40 m mesh size) Z = 1500 mZ = 2500 m >10

5. Implementing 3D Turbulence … Validation step: Validation of 3D turbulence code against published LES results 3D LES-type turbulent diffusion scheme with 40-m runs. Study of impacts: Impact on structure of urban boundary layer Comparison of 1D versus 3D turbulence code with 250-m runs in Oklahoma City in July 2003 Comparison and assessment on 1-km and 250-m runs.

6. Vertical heat flux: published LES results Moeng et al., J. Atmos.,Sci., 1994 30 m resolution SB1 and SB2: strong shear + moderate convection SGS (sub-grid-scale parameterization) model mostly active: - lower levels (near surface) -top of PBL (entrainment zone)

7. Vertical heat flux: resolved and subgrid scales (OKC 16:00 CDT) 40 m200 m

8. 3D_LES_KC option 3D_MESO option Model : MC2 v4.9.8 Phy. v4.3.1 Resolution : 40 m 40 m Vertical heat flux: resolved and subgrid scales (OKC 16:00 CDT)

9. 3D_LES_KC option 3D_MESO option Model : MC2 v4.9.8 Phy. v4.3.1 Resolution : 40 m 40 m Vertical heat flux: resolved and subgrid scales (OKC 16:00 CDT) - “zoom” on bottom 300 m -

10. 3D_LES_KC option 3D_MESO option Model : MC2 v4.9.8 Phy. v4.3.1 Resolution : 40 m TKE resolved and subgrid scales (OKC 16:00 CDT) 40 m

11. … Implementing 3D Turbulence Validation step: Validation of 3D turbulence code against published LES results 3D LES-type turbulent diffusion scheme with 40-m runs. Study of impacts: Impact on structure of urban boundary layer Comparison of 1D versus 3D turbulence code with 250-m runs in Oklahoma City in July 2003 Comparison and assessment on 1-km and 250-m runs.