ROMS as a Component of the Community Climate System

Model (CCSM)

Enrique Curchitser, IMCS/Rutgers

Kate Hedstrom, ARSC/UAFBill Large, Mariana

Vertenstein, Don Stark, and Jon Wolfe, NCAROctober, 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– 1958-2004

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 ExecutionIce

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