ROMS as a Component of the Community Climate System Model (CCSM)

1. ROMS as a Component of the Community Climate System Model (CCSM) Enrique Curchitser, IMCS/Rutgers Kate Hedstrom, ARSC/UAF Bill Large, Mariana Vertenstein, Don Stark, and Jon Wolfe, NCAR October, 2007

2. Climate Model Biases

3. The Regional Setup

4. SST, August 18, 2000

7. Need to downscale atmosphere as well! 9+27 km forcing COAMPS ~ 200 km forcing (CORE)

8. 10 km average horizontal resolution Run10: 42 vertical layers Coupled sea ice and ocean Six-hourly fluxes from Common Ocean-ice Reference Experiments (CORE) reanalysis IC’s and BC’s from CCSM (POP) forced by CORE 1958-2004 NEP Implementation

9. Evaluation of Latest Simulation • We are much happier with the heat fluxes from CORE than from NCEP • Ice area seems quite realistic • Still could do better: • Not enough fresh water input at the coast • Stratification in general isn’t quite right, will perhaps be improved by tidal mixing, different IC/BC • We want a shallower minimum depth • We also need to add an ecosystem model for GLOBEC

10. Ice Area and Volume

12. CCSM Coupling • Thanks to the CORE group’s products, we no longer need to run the large NPAC domain (proof of one-way coupling) • The CCSM model does fine for its resolution, but fails in regions needing more resolution • The idea is to couple ROMS to CCSM, where ROMS is part of a “composite ocean” providing a better sea surface temperature to the atmosphere

13. CCSM

15. Standalone ROMS (ocean.h) #include “cppdefs.h” PROGRAM ocean USE … #ifdef MPI CALL mpi_init CALL mpi_comm_rank(…) #endif CALL initialize CALL run CALL finalize #ifdef MPI CALL mpi_finalize #endif END PROGRAM ocean

16. Standalone ROMS (nl_ocean.h) • Included by ocean_control.F • Contains initialize, run, finalize for the nonlinear ocean model • Run calls main3d or main2d inside the timestepping loop • Calls get_data which reads files (both in initialize and in run)

17. Coupled Mode • Composite ocean knows input filename, NtileI, NtileJ, dt, and ntimes • Two phase ROMS initialization, first calls inp_par, second calls get_data • get_data copies fields from CAM • run is called each coupling interval

18. CCSM Strategy • The coupling interval is one day, with the atmosphere running ahead • The composite ocean will receive hourly winds, etc. and interpolate to ROMS grid(s) • POP runs for that day, sends “curtains” out for ROMS nests • ROMS runs for that day • Composite ocean merges SST from POP and ROMS for CAM

19. Concurrent Execution Ice From Dan Schaffer

20. Sequential Execution Ice From Dan Schaffer

21. CCSM is now concurrent, with differing numbers of processors for each of the components • An effort is underway to make it sequential, for the IBM Blue Gene and other such computers • The ROMS coupling strategy described is more sequential

23. Patches • More than one simultaneous patch • Can now handle through Ngrids feature • Trouble: • Southern ocean (ICE and ICE_SHELVES) • Bering (ICE, TIDES, and ECOSYSTEM 1) • Peru (ECOSYSTEM 2) • What to do?

24. Conclusions • We are excited about this opportunity to work with the CCSM group • A similar effort is underway to add WRF as a regional atmospheric model • Very much a work in progress, still to be done: • POP “curtains” to ROMS • SST back to composite ocean • Changing to CCSM bulk_flux algorithm