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)

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?

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)

“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

“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

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.”

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)

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

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

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)

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

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

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

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

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!

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

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

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

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

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

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

Nudge: Distribution of RMSEs and RMSEu by Day

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

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

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

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 DW13921548. 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.