Warm Season Diurnal Cycle Simulations Over North America - Sensitivities to Model Resolution

1. Warm Season Diurnal Cycle Simulations Over North America - Sensitivities to Model Resolution Myong-In Lee1,2, Siegfried Schubert2, Max Suarez2, Julio Bacmeister2, Phil Pegion2, Isaac Held3, Gabriel Lau3, Jeff Ploshay3, Arun Kumar4, Jae Schemm4, Hyun-Kyung Kim4, and Soo-Hyun Yoo4 1 Goddard Earth Science and Technology/ UMBC 2 Global Modeling and Assimilation Office, NASA/GSFC 3 Geophysical Fluid Dynamics Laboratory, NOAA 4 Climate Prediction Center, NCEP

2. NOAA/OGP proposal: “An Assessment and Analysis of the Warm Season Diurnal Cycle over the Continental United States and Northern Mexico in Global Atmospheric General Circulation Models” assess and analyze the diurnal cycle in the NASA, NCEP and GFDL AGCMs 2) improve our understanding of the important physical processes that drive the diurnal cycle 3) provide guidance for development of physical parameterizations http://janus.gsfc.nasa.gov/~milee/diurnal

3. Outline 1. Diurnal Cycle of Precip in 3 AGCMs (in climate resolution) 2. Sensitivity to Horizontal Resolution 3. Cumulus Convection Scheme Test 4. Summary

4. Description of Models

5. Experiments and Validation • Ensembles of 5-Month Hindcasts • 5 members with different IC, starting 1 May • analyze warm season of Jun-Aug • SST climatology (1983-2002) prescribed • Validations • NCEP Hourly Precipitation Data (HPD) • NCEP North American Regional Reanalysis (NARR) 3-hourly

6. JJA Precipitation and 925mb Winds: 2-Degree Resolution Reanalysis

7. Phase (local time) of Maximum Precipitation (24-hour cycle) Observations local time

8. Sensitivity to Resolution

10. Local Time

11. 6pm 6pm 6pm 6pm 9pm 9pm 9pm 9pm Observations GFDL NCEP NASA 12pm 12pm 12pm 12pm Eastward Propagation?

12. Diurnal Cycle in GP Region precip, wind 925 hPa

13. Diurnal Cycle in GP Region precip, wind 925 hPa

14. Diurnal Cycle in GP Region precip, wind 925 hPa

15. North American Monsoon Region

16. Diurnal Cycle in NAME Region precip, wind 925 hPa

17. Diurnal Cycle in NAME Region precip, wind 925 hPa

18. Diurnal Cycle in NAME Region precip, wind 925 hPa

19. Time-mean Precip and w925(1/2 degree resolution) NASA GFDL NCEP mm/day m/s

20. NARR NSIPP

21. Diurnal Cycle from NERN Observation (Dave Gochis)

22. Phase of Diurnal Cycle (1/2 degree resolution, p>0.1) NASA GFDL NCEP

23. Description of Convection Scheme

24. Sensitivity to Treatment of Convection Scheme(NASA/GMAO Model) Relaxation Time Scale Sub-cloud Layer

25. Phase of Diurnal Cycle of Precipitation NASA with GFDL parameters NASA CNTL TRMM

26. Concluding Remarks • Diurnal cycles of precipitation are differently simulated among the models, while the models have basically similar convective schemes (buoyancy closures) • Increased resolution has mixed impact on the simulated diurnal cycle of convection • it resolves some of the key local features (e.g. land-sea breeze and topographic impacts) • it improves the initiation and propagation of precipitation over the Rockies • but, highest resolution tends to dry out the Great Plains • The major differences in diurnal cycle simulation appear to be in the implementation details of the convection scheme and the interaction with the boundary layer; this suggests the need for improvement in model physics parameterizations

27. Thank you !!

28. LLJ Frequency Simulation (nighttime 06 Z + 12 Z Composite) GFDL NARR (1995) NCEP NASA

29. [mm/day]

31. Significant Test • Rainfall (R) in each grid point is assumed to sinusoidal harmonics in a day • Coefficients of amplitude (r) in daily are tested with the 90 % confidence level (p < 0.1)

33. 6pm 6pm 6pm 6pm 9pm 9pm 9pm 9pm Observations GFDL NCEP NASA 12pm 12pm 12pm 12pm Eastward Propagation?

34. GFDL NCEP NASA 6pm 6pm 6pm 9pm 9pm 9pm 12pm 12pm 12pm 1- Degree Runs in Three AGCMs Small hint of eastward propagation but suppressed over the GP region

48. Phase of Diurnal Cycle- NASA (p>0.1)

49. Phase of Diurnal Cycle- NCEP (p>0.1)

50. Phase of Diurnal Cycle- GFDL (p>0.1)