1. VISTAS Grid Resolution Sensitivity
Ralph Morris, Bonyoung Koo and Steven Lau
ENVIRON International Corporation Gail Tonnesen, Zion Wang, Chao-Jung Chien University of California at Riverside T.W. Tesche and Dennis McNally Alpine Geophysics National RPO Modeling Meeting
Denver, Colorado
May 24-25, 2004

2. Grid Resolution Sensitivity
Three VISTAS Phase I Episodes
January 2002
July 1999
July 2001
MM5 PX_ACM(2)
36 km national RPO grid and 12 km Southeast US VISTAS Grid
Examine Model Performance in VISTAS Southeast US Domain

3. VISTAS Phase I 36/12 km Domains

4. SO4 IMPROVE 36 km vs. 12 km
January 2002 – SO4
July 1999 – SO4

5. WSO4 NADP 36 km vs. 12 km
January 2002 – WSO4
July 1999 – WSO4

6. July 2001 36 km vs. 12 km July 2001 – SO4 IMPROVE
July 2001 – WSO4 NADP

7. IMPROVE SO4 Fractional Bias and Error CMAQ 36 km and 12 km & CB4 and SAPRC99

8. IMPROVE NO3 Fractional Bias and Error CMAQ 36 km and 12 km & CB4 and SAPRC99

9. IMPROVE OC Fractional Bias and Error CMAQ 36 km and 12 km & CB4 and SAPRC99

10. Ozone Performance July 1999 Episode CMAQ and CAMx at 36 km and 12 km (CB4)
CMAQ ozone performance degradation to under-estimation with finer grid
CAMx ozone performance similar at 36 km and 12 km

11. CAMx 36/12/4 km Performance for MRPO June 18 – August 13, 2001 Episode
Mean Normalized Bias
Degradation in most gas-phase species with higher resolution
Aerosol species stay same or improve

12. CAMx 36/12/4 km Performance for MRPO June 18 – August 13, 2001 Episode
Mean Normalized Gross Error

13. Conclusions: Grid Resolution Sensitivity
Effects of grid resolution on model performance is mixed
Changes in precipitation patterns and magnitudes can have large effect locally
Changes in transport patterns also can have big local effect (e.g., Jim Boylan’s analysis of sulfate clouds)
12 km grid technically superior for grid modeling than 36 km, but still does not resolve point sources and urban areas very well
12 km takes more CPU time than 36 km
VISTAS Phase II annual modeling will use both 36 and 12 km grids