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

Climate Model Biases

The Regional Setup

SST, August 18, 2000

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

NEP Implementation 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 –

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

Ice Area and Volume

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

CCSM

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

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)

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

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

Concurrent Execution Ice From Dan Schaffer

Sequential Execution Ice From Dan Schaffer

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

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?

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