1. The Value of Nudging in the Meteorology Model for Retrospective CMAQ Simulations
Tanya L. Otte NOAA Air Resources Laboratory, RTP, NC (In partnership with U.S. EPA National Exposure Research Laboratory)

2. Motivation
How do “improved” meteorological fields (i.e., that include nudging) impact the AQ simulation?
Do nudged met fields improve AQ “predictions”?
Does an air quality simulation forced by nudged meteorological fields degrade? If so, when?
How quickly does an air quality simulation forced by forecast meteorological fields degrade?
What are the implications for AQ forecast length?
Which fields have the greatest impact on CMAQ?
Can we improve upon or redefine de facto standard for meteorology simulation style?
Can we improve the application of nudging in meteorology model?

3. What is “Nudging”? Formally, “Newtonian relaxation”
Method of dynamically relaxing model toward observed state
Artificial forcing term in prognostic eqn
Uses difference between model & ob
One method of FDDA in MM5 (& WRF)

4. “Typical” MM5 Simulation for AQM
Run for MM5 for ~5.5-day period
Use nudging throughout simulation (i.e., a “dynamic analysis”) to keep meteorology as close to observed as possible
Use “analysis nudging” for 36-km runs

5. “Typical” MM5 Simulation for AQM
7920 minutes = 132 hours = 5.5 days
Day 1
Day 2
Day 3
Day 4
Day 5
5 Days of Input Meteorology for CMAQ
12 h for
“MM5 spinup”
Day 6
Day 7
Day 8
Day 9
Day 10
5 Days of Input Meteorology for CMAQ
Day 5 Hours 13-24

6. Experiment Design 36-km CONUS domain; summer 2001
Run AQM suite using two met. runs
Standard AQM met setup (i.e., with nudging)
Standard AQM met, but without nudging
Allow emissions to reflect different met.
Analyze met. and AQ by “day within met.”

7. Meteorology MM5v3.6 Radiation: RRTM LW, Dudhia SW
Microphysics: Reisner 2
Convection: KF2
PBL & LSM: ACM and P-X
Nudging: 3-h NAM/Eta analyses
U, V, T (G = 3.0 x 10-4 s-1)
q (G = 1.0 x 10-5 s-1)

8. Emissions 2001 NEI SMOKE v2.2 MOBILE6, BEIS3
Sectors rerun for meteorology:
Biogenics
Plume rise

9. Air Quality CMAQv4.6 34 layers (no collapsing) Dry Dep: M3Dry
Mechanism: CB05
Aerosols: AERO4
PBL: ACM2
LBC: GEOS-CHEM

10. Study Period 30 Jun – 3 Aug 2001 MM5: CMAQ:
12 UTC 19 Jun – 00 UTC 4 Aug
5.5-day reinitialized segments
First 12-h not used by CMAQ
CMAQ:
00 UTC 20 Jun – 00 UTC 4 Aug
1-day (continuous) segments
First 10 days are not analyzed (spin up)

11. Results… Shown by “Day n” Runs called “Nudge” and “Nonudge”
Observations:
Met: surface only
AQ: AQS ozone
Use AMET for first look
Results shown are preliminary

12. Dates (2001) by Placement in MM5 Run Segment
Day 1
Day 2
Day 3
Day 4
Day 5 3
30 Jun
1 Jul
2 Jul
3 Jul
4 Jul 4
5 Jul
6 Jul
7 Jul
8 Jul
9 Jul 5
10 Jul
11 Jul
12 Jul
13 Jul
14 Jul 6
15 Jul
16 Jul
17 Jul
18 Jul
19 Jul 7
20 Jul
21 Jul
22 Jul
23 Jul
24 Jul 8
25 Jul
26 Jul
27 Jul
28 Jul
29 Jul 9
30 Jul
31 Jul
1 Aug
2 Aug
3 Aug

13. Meteorology 2-m Temperature 10-m Wind Speed MAE MAE IA IA Bias Bias
Nonudge
MAE
Nudge
MAE
JJA 01
(Gilliam et al., AE, 2006) IA IA
Bias
Bias

14. Meteorology
Nudge generally better than Nonudge, as expected and widely published
Shown in 2-m temperature and 10-m wind speed
2-m moisture and 10-m wind direction have similar results
Less impact in wind than temperature due to nudging surface wind analyses
Additional analysis remains
PBL heights and variables
Precipitation and clouds
Upper-air fields

15. Air Quality Is nudging met. important for AQ?
Use AQS hourly surface ozone
Large network
Wide spatial coverage
Observations can be binned by day
AMET: AQ days in LST, not UTC!

16. 1-h Maximum Ozone (AQS): RMSE – Day 1
No Nudging
With Nudging

17. 1-h Maximum Ozone (AQS): RMSE – Day 2
No Nudging
With Nudging

18. 1-h Maximum Ozone (AQS): RMSE – Day 3
No Nudging
With Nudging

19. 1-h Maximum Ozone (AQS): RMSE – Day 4
No Nudging
With Nudging

20. 1-h Maximum Ozone (AQS): RMSE – Day 5
No Nudging
With Nudging

21. Meteorology and Air Quality By Day (RMSE)
2-m Temperature and 10-m Wind Speed
1-h Maximum Ozone
1-h max O3 RMSE
2-m temp RMSE
1-h max O3 RMSEu
1-h max O3 RMSEs
10-m wind RMSE

22. Nudge: Distribution of RMSEs and RMSEu by Day

23. 1-h Maximum Ozone (AQS East): RMSEs and RMSEu
Nonudge
RMSEu
Nudge
Nonudge
RMSEs
Nudge

24. 1-h Maximum Ozone (AQS East): Index of Agreement
Nudge
Nonudge
Days 5, 1, 2

25. Summary
Using nudging for “dynamic analysis” in MM5 is critical for retrospective air quality simulations for ozone
Nudging generally superior (as hoped!)
Justifiable to delay jump to WRF
Still cannot make firm conclusions
Impact of met. on AQ needs to be quantified
Other meteorological variables, emissions, additional chemical species

26. Acknowledgments L. Reynolds (CSC): MM5 preprocessing and MM5 nudge run
A. Beidler, C. Chang, and R. Cleary (CSC): MM5-independent emissions
G. Pouliot: Guidance on MM5-dependent emissions
G. Sarwar: Photolysis files
S. Howard: GEOS-CHEM-based LBCs for June and July
S. Roselle: CMAQ initial conditions and executable
R. Gilliam and K. W. Appel: AMET support
The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.