CCAM Regional climate modelling

1. CCAM Regional climate modelling Dr Marcus Thatcher Research Scientist December 2007

2. Overview • This presentation describes CCAM climate downscaling • Specifically, we downscale from NCEP 2.5 deg reanalyses to 60 km resolution climate simulation • The output can then be processed using NCO toolkit for netCDF files to create climate averages, etc. • These results can then be compared to downscaled climate projections (e.g., CSIRO Mk3) CMAR RCM

3. Regional Climate Modelling with CCAM • RCM is achieved with a multiple nesting procedure, by first downscaling to 60 km resolution and then downscaling to 15 km resolution Mk3 CCAM 15km CCAM 60km Comparison of average rainfall (mm/day) between Mk3, CCAM at 60 km resolution and CCAM at 15 km resolution for northern Queensland CMAR RCM

4. Regional Climate Modelling with CCAM • The climate downscaling script can be found at • $HOME/ccam/scripts/clim/pd60_run • This script will generate a ten year downscaled climate run for Indonesia (this takes a long time to run!) • Today we will simply start the script running and examine the first month of output CMAR RCM

5. Instead of preparing initial conditions, we must first prepare the host model from which to downscale. Usually we downscale from NCEP 2.5 degree reanalyses Alternatively we downscale from CSIRO Mk3 climate projections However, any model once prepared on the CCAM grid can in theory be used (e.g., ERA-40) Host model – NCEP reanalyses Aerosols and CO2 data Host model Interpolated to C48 CCAM grid Run 60 km CCAM for Indonesia Process output for climatology CMAR RCM

6. Next the aerosols for a particular year must be prepared for CCAM This is achieved using the aero_m20.sh script. The aerosol data files are located at $HOME/ccam/stdin/sulfateA2.???? Note that the aerosol data files are valid from 1961 to 2100 Aerosol input CO2 data Aerosols (aero_m20.sh) Run 60 km CCAM for Indonesia CMAR RCM

7. The CO2 levels must also be specified for a CCAM climate run. These files also are valid from 1961 to 2100 and are located at $HOME/ccam/stdin/co2_data.???? Note that there is no preprocessing of CO2 files since (unlike aerosols), the CO2 levels are independent of position However, the CO2 files only work for CCAM with 18 vertical levels. For different vertical resolution, the CO2 data files need to regenerated CO2 input CO2 data Aerosols (aero_m20.sh) Run 60 km CCAM for Indonesia CMAR RCM

8. The CCAM namelist for climate simulations is also slightly different to the NWP example. CCAM switches used for climate simulations are listed as follows: nbd = 0 (disable far field nudging) mbd = 20 (spectral nudging) kbotdav = 10 (nudge upper levels only) CCAM namelist options for climate downscaling CMAR RCM

9. Sigma levels kbotdav=4 (typically NWP) kbotdav=10 (typically climate) CMAR RCM

10. CCAM climate simulation • When performing a climate simulation, we run only one month at a time. • Once the month simulation is complete, it creates a restart file which is used to initialise CCAM for the next month NCEP 2.5 degree reanalysis host model (nudging) CCAM simulation (Mar) CCAM simulation (Feb) CCAM simulation (Jan) Restart file Restart file CMAR RCM

11. CCAM restart files • If CCAM stops during a long climate run (e.g, electricity black-out), then the climate simulation can be restarted from the last restart file • Also, the restart files are usually archived so that CCAM can be restarted from any month during the climate simulation CMAR RCM

12. CCAM climate simulation • CCAM restart files are called • $HOME/ccam/scripts/clim/RESTART/Restccam_NCEP_60.?????? • Typically we tar the files from the same year • The daily CCAM output can be found at • $HOME/ccam/scripts/clim/daily • The monthly averaged CCAM output is • $HOME/ccam/scripts/clim/monthy_mean • The raw CCAM output (from which the above files can be regenerated) is • $HOME/ccam/scripts/clim/OUTPUT CMAR RCM

13. CCAM output • Below is an example cc2hist namelist &input kta=720 ktb=999999 ktc=720 minlat = -20., maxlat = -10., minlon = 90., maxlon = 120. use_plevs = T plevs = 1000, 850, 700, 500, 300 &end &histnl htype=“ave" hnames= "all" hfreq = 0 &end Every 12 hours Output domain Use and define Pressure levels (instead of sigma levels) Generate average CMAR RCM

14. NCO toolkit for NetCDF files • CCAM output can also be processed using the NCO toolkit for manipulating NetCDF files • Specifically, the ncea program for averaging NetCDF files is a quick way to calculate the average climate (i.e., for study) CMAR RCM

15. Other types of climate run • There are several different versions of CCAM climate runs, depending on the application • NCEP 2.5 deg reanalyses: • Used to test CCAM downscaling with ‘observed’ present day or historical weather behaviour. • CSIRO Mk3 control run: • Nesting CCAM in a simulated present day climate to test the performance of CCAM when there are biases in the host model • CSIRO Mk3 climate projection: • Nesting CCAM in simulated future climate to predict regional changes arising from increasing global temperatures. CMAR RCM

16. Some RCM examples • The following slides show some examples of RCM with CCAM • In these examples we show Australia • However, during the tutorial we can start to create examples for Indonesia CMAR RCM

17. Obs Tmax CCAM-m DJF 30-year run, downscaled from Mk3 CGCM JJA

18. Obs Tmin CCAM-m DJF JJA

19. Obs Rainfall (mm/d) CCAM-m DJF JJA

20. Tropical cyclone days/year – observed vs model New CCAM – 30 yr climatology 10 ms-1 threshold Obs – 30 yr climatology Latest 60 km simulations produce good climatology of “cyclone-like” vortices. Above shows example of C-CAM downscaled from Mk3 CGCM CMAR RCM

21. Multiple nesting for climate simulations • Like the CCAM NWP forecasts, it is possible to downscale the 60 km climate run to 15 km resolution by multiple nesting of the forecast • However, given the small time step for the 15 km simulation, this takes a very long time to simulate (multiprocessor CCAM is a necessity) CMAR RCM

22. Average maximum temperature (deg C) OBS - Jan CCAM - Jan OBS - Apr CCAM - Apr CCAM - Jul OBS - Jul OBS - Oct CCAM - Oct CMAR RCM

23. Average minimum temperature (deg C) OBS - Jan CCAM - Jan OBS - Apr CCAM - Apr CCAM - Jul OBS - Oct CCAM - Oct OBS - Jul CMAR RCM

24. Average rainfall (mm/day) CCAM - Apr OBS - Apr CCAM - Jan OBS - Jan OBS - Jul CCAM - Jul CCAM - Oct OBS - Oct CMAR RCM

25. Missing data in the highly stretched region is replaced with weather information from the previous, lower resolution forecast CCAM uses a multiple stretched grid technique to ‘step down’ or downscale the forecast CCAM technical notes 60km 8km 1km CMAR RCM

26. Global nudging Far-field nudging Full nudging of far-field winds in the free atmosphere, with e-folding time ~24 h Full nudging of fields in the free atmosphere, with e-folding time ~48 h No nudging (only SSTs) Partial nudging Model uses NCEP or GCM winds only outside the inner red boundary Model uses NCEP or GCM winds (and optionally other fields) at all points For long, variable-resolution climate runs (only), some nudging is desirable to assist the climatology in the coarsest part of the globe

27. 8 km resolution No hard boundaries at panel edges: Far-field nudging from 60 km model run on this panel Rest of world 8 km resolution throughout this panel About 50 km resolution at this edge CMAR RCM

28. Far field nudging CMAR RCM

29. Advanced CCAM configuration • CCAM can now also use spectral downscaling, although it is slower than far field nudging • Spectral downscaling modifies the large scale structure of the atmosphere to be the same as the host model everywhere 60km The large scale structure of the atmosphere is nudged everywhere 8km Small scale structure is not perturbed CMAR RCM

30. Spectral nudging CMAR RCM

31. Thank You Contact CSIRO Phone 1300 363 400 +61 3 9545 2176 Email enquiries@csiro.au Web www.csiro.au Marine and Atmospheric Research Name Dr Marcus Thatcher Title Research Scientist Email Marcus.Thatcher@csiro.au