Comparison of online and offline modeling with WRF/chemT

1. Comparison of online and offline modeling with WRF/chemT Julius S. Chang (張時禹） Institute of Atmospheric Physics National Central University, Taiwan

2. Participants in WRF/chemT development: Julius S. Chang, Shu Wei Hsu, Tsun Hsien Liu, Tu fu chen, Jing Li, and Chi Kang Chiang

3. Outline of Presentation • On the concept of off-line and online models • What is WRF/chemT? • How is it different from • WRF/chem? • Some preliminary findings

4. Coupling of Atmospheric Processes Off-line model: Step 1 Meteorological Model Conservation of energy, mass, and momentum Emissions Model Step 2 Anthropological and biogenic emissions Air Quality Model Step 3 Conservation of chemical species

5. Domain 1

6. Typical Nested Domains Harbin Shenyang Beijing Seoul Jinan Pusan Xi'an Tokyo Osaka Nanjing Fukuoka Wuhan Shanghai DOMAIN 1 Chongqing DOMAIN 2 Taipei Guangzhou DOMAIN 3 Hanoi DOMAIN 4 HongKang Kaohsiung Manila

10. WRF/chemTa new direct coupled meteorology and chemistry model • It is derived from WRF/chem • The philosophical departure is to focus on selected options and improvements of only those options. • At NCU we assume responsibilities for correct operations of this “reduced and modified” model. • When useful, our submodels will be offered to WRF/chem working group for consideration for the “mother” model.

11. WRF-chem development • Original WRF-chem is WRF + RADM2+ . . . mostly ported from offline models. • Some of the major issues are: 1. Computationally slow It is desirable to be faster 2. incomplete direct coupling of emissions Not really “online” 3. Incomplete direct coupling of other processes more recent versions are better

12. Computaional efficiency of WRF-chem For a particular five day simulation over a Taiwan domain using 128CPUs WRF (meteorology only): 939 sec WRF-chem (met. and gas chemistry): 3905 sec Not including aerosol or aq. chem.!

13. 3-D Air Quality Model (AQM) AQM describes atmospheric transport, transformation and deposition of airborne chemical species via a set of species conservation equations. transport diffusion source dry deposition gas-phase chemistry cloud process etc.

14. Symbolically this set of partial differential equations can be written as Or even more briefly as

15. To simplify the symbols and after discretization, we use the vector notation Apply Operator Splitting

16. Comparison of chemical solvers for WRF/chem 2.x and WRF/chemT 2 times faster 3 times faster 4 times faster

17. To simplify the symbols and after discretization, we use the vector notation Apply Operator Splitting

18. A most important advantage of this new approximation is the resulting computational algorithm

19. Test Case

20. Emissions processing for WRF/chem WRF Emission Model WRF/chem 3.x Met. Proc. Emissions Proc. Emissions processing for WRF/chemT WRF/chemT meteorology emissions chemistry

21. Coupling of Atmospheric Processes Online model Meteorology point and anthrop. sources cloud, precipitation radiation, energy balance Emissions photolysis, aerosol, cloud, wet chemistry, depositions Air Quality

24. Asymmetric convective model (ACM) • Developed as simple as the Blackadar model with a modified scheme for the downward mixing. • Strongly buoyant plumes rise from the surface layer to all leves in the CBL but downward motion is primarily a gradual compensating subsidence.

25. Modified Asymmetric convective model (ACM2) • combines the non-local convective mixing of the original ACM with local eddy diffusion to better represent the full range of turbulent transport.

30. Surface ozone around Taiwan from WRF-chemT with two different sets of boundary conditions

33. Observed and Simulated Data

34. Thank you for your attention!