Development of WRF-CMAQ Interface Processor (WCIP)

1. Development of WRF-CMAQ Interface Processor (WCIP) Seung-Bum Kim and Daewon W. Byun University of Houston Air Quality Modeling and Monitoring Center

2. Development of WCIP Background: NCAR/NOAA/Air Force is Developing Weather Research and Forecasting (WRF) model to replace MM5 & NCEP Eta Goal: Build consistent on/off-line WRF-chem model Objectives: • Demonstrate that CMAQ’s Fully-Compressible Governing Set of Equations (FCGSEs) is Dynamically Consistent with WRF Eulerian Dynamic Cores: Mass (EM), Height (EH) • Provide algorithms for the WCIP implementation • Mass conservation test of MM5, WRF-EH, WRF-EM with CMAQ

3. CMAQ FCGSEs and WRF Dynamic Cores (1) Horizontal Momentum Equation Vertical Momentum Equation horizontal wind vector on the reference earth-tangential Cartesian coordinates Contra-variant wind components used in CMAQ

4. CMAQ’s FCGSEs and WRF Dynamic Cores (2) Conservation Equations Air Density Entropy Density Pollutants Entropy Density Diagnostic Equations Ideal Gas Law Pressure

5. WRF Eulerian Mass (EM) Dynamic Core (1) Vertical Coordinate: terrain following, time dependent hydrostatic pressure (p) Wind components Vertical momentum Eq.

6. WRF Eulerian Mass (EM) Dynamic Core (2) Conservation Equations WRF Eulerian Height (EH) Dynamic Core

7. WCIP Met. Algorithms for EM Core Mass-Jacobian weighted Contravariant wind components Comparison of WRF- W with omega-equation needed WCIP Met. Algorithms for EH Core

8. Mass conservation test of MM5, WRF-EH, and WRF-EM with CMAQ Purpose: To quantify the mass consistency of each model To find out possible problems in on/off-line WRF-chem modeling

9. Experimental Design

11. Major functions of current WCIP • Read WRF data • Reconcile coordinate • Horizontal interpolation • Compute Jacobian, entropy, density, etc. • Current WRF does not provide • enough PBL parameters needed in • CMAQ. We had to use PBL diagnostic • routine built in MCIP in this • implementation

12. Treatment of missing met. variables in WCIP • surface roughness, albedo, emissivity, surface moisture availability  use MCIP2 values • latlon and map scale factor on dot grids  interpolation using those on cross grids • Pressure, density at full layers  diagnosed by using ideal gas law To avoid errors from interpolation or approximation, we better ask WRF group to make special output procedure for AQ modeling group

13. Jacobian of WRF EM 06 UTC 18 UTC Jacobian-weighted density varies with time, but it is constant vertically in WRF EM coordinate

14. MM5 WRF height Jacobians of MM5 and WRF EH

15. Difference of Initialization process • Although we tried to make comparable MM5 and WRF outputs in this experiment, we have found MM5 initialization routine provides organized vertical wind field initially, but, for some reason, WRF SI routine does not generate any initial vertical motion. • However, initial horizontal motion field was quite similar.

16. Vertical Velocity at surface layer 2000/08/26/00UTC (Initial Time) MM5 WRF mass zero field

17. Benefit of WRF EM • The benefit of WRF EM over WRF EH is that the tendency of Jacobian-weighted density shown in coordinate transform becomes the tendency of surface pressure in WRF EM, so that the vertical wind can be determined based on the divergence in the layer and the tendency of surface pressure term. • This can be still applied to non-hydrostatic fully compressible atmosphere as long as we rely on hydrostatic pressure as coordinate.

18. Contravariant Vertical Velocity in WRF EM dynamical core The tendency eq. for the surface hydrostatic pressure from continuity eq. in the ideal case using the boundary conditions at top and bottom : Since eta is a material coordinate, the air density does not explicitly appear in the continuity equation. Therefore, it can be used to estimate the contravariant vertical velocity component by integrating the wind divergence term either from the bottom to a level eta or from the top to eta: (downward integration) (upward integration)

19. Difference of vertical momentum component in generalized coordinate Gravity wave pattern  WRF may need normal mode initialization, because this pattern is not realistic !!!

20. Mass conservative temporal interpolation method (I) The Jacobian and density at a time Wind components multiplied with Jacobian-weight density are interpolated linearly,

21. Mass conservative temporal interpolation method (II) Finally, interpolated wind components are derived with:

22. Vertical velocity multiplied with Jacobian-weighted density2000/08/26/06UTC MM5 WRF mass WRF height

23. PBL height WRF mass MM5 WRF height

24. MM5 WRF mass Vertical Velocity at surface layer 2000/08/26/20UTC (14LST) (31,50)

25. Normalized IC1_BC1 concentrationVertical velocity (in WRF mass) RED: w-component on mass coordinate directly from WRF mass BLACK: vertical velocity on mass coordinate in WCIP using omega equation Hourly WRF EM data have mass consistency !!!!

26. Normalized IC1_BC1 concentrationMM5, WRF mass, WRF height(No Collapsing) In spite of existence of gravity wave mode, WRF EM shows mass consistency characteristics as good as MM5 or a little bit better.

27. Normalized IC1_BC1 concentrationEffects of Collapsing Collapsing damages mass conservation characteristics significantly!!!

28. Are high frequency met. data always better?Time Resolution Issue This result shows us that high-frequcy met. data might be worse for mass conservation  need the consistent numerical transport algorithm between meteorological and chemistry-transport model

29. Summary and Conclusions • On the way we develop consistent on/off-line WRF-chem model, 1) Reliable WCIP has been developed. 2) We need to communicate with WRF group on the following issues: • Although many met. parameters needed in the CMAQ are calculated in the WRF, they are not included in standard output of WRF presently. • According to the mass conservation test, we need build consistent transport numerical algorithms both in WRF and CMAQ