______________________________________________ _\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\\_\ MULTI-LAYER MIXED-LAYER OCEAN MODEL CODE 913, NASA/GODDARD SPACE FLIGHT CENTER FANGLIN YANG, 2003 _\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\\_\ ______________________________________________ Preface A 30-layer mixed-layer ocean model with global coverage was developed when I worked at the Climate and Radiation Branch, NASA Goddard Space Flighty Center. The core of this model is a one-dimensional MLO based on the work of Gaspar (J. Physical Oceanography, 1988). This 1-D model can be used independent of the global model. Some features of the global MLO are similar to those of Michael Alexander's MLO (Battisti et al., J. Climate 1995). In principle, this is a column model. There is no horizaontal advection. Flux corrections for heat and salinity are derived from training to represent the transport of heat and water mass by oceanic currents. Within the mixed layer, temperature and salinity are prognostics. Mixed-layer depth is prognostics when entrainment occurs, and is diagnostics when mixed layer shoals. In layers below the mixed layer, vertical diffusion, convective adjustment and solar radiation pentration are included. In addition, temperature and salinity at layers below the mixed layer are also relaxed to observed climatologies in a 10-year time scale. Language Fortran 90 is the standard, ocassionally mixed with Fortran 77. I have tried my best to use online documentation so that users can understand the model without much a headache. So please read the code if you have questions not answered in this short note. Model Structure Both the vertical and horizontal resolution of the model can be easily changed by modifying the files ending with .h in the directory ./code. Documented here is a 30-layer MLO suitable for the NASA fvGCM at 2x2.5 horizontal resolution. All plots (.eps files) included in this tar file are for the fvGCM2x2.5 MLO30 model. The MLO extends down to 1000 meter, or the depth of the ocean if the bathymetry is less than 1000 m. For points shallower than 50 m, they are treated as a slab ocean. vertical structure of the model --------------------------- surface --------------------------- k=1, dz(1), zlev(1) --------------------------- k=2, dz(2), zlev(2) . . . --------------------------- ^^^ h, bottom of mixed layer --------------------------- k=laymix . . . --------------------------- k=km, dz(km), zlev(km) How to Construct Your MLO You may replace "30" and "fvgcm2x2.5" in the following with your model vertical layers and GCM id. 1. unpack the mlo_yang.tar file in a directory, say, ./mlo 2. set up desired vertical layers by changing ./mlo/code/mlo.h and gridz30.h. set up horizontal grid consistent with input/GCM grid by changing ./mlo/code/gridxy_fvgcm2x2.5.h 3. Prepare boundary and initial conditions. a). goto ./mlo/ics_bcs/mask_fvgcm, produce a land-sea mask file, name it as mask_fvgcm2x2.5, then make symbolic links at ./mlo/ics_bcs, and name them as mask_fvgcm2x2.5 and mask_mlo_fvgcm2x2.5. For my case, these two files are the same. But mask_mlo_fvgcm2x2.5 can be set differently from mask_fvgcm2x2.5 if you want to run the MLO over only certain oceanic regions. b). goto ./mlo/bathymetry, determine active MLO layers from world ocean bathymetry dataset by running cnvt_fvgcm2x2.5.f. make a symbolic link of the file bathy_fvgcm2x2.5 at ./mlo/ics_bcs. d). goto ./mlo/watertype, run type_fvgcm2x2.5.f to set up optical water types, which are used to compute the penetration of solar radiation in water. make a symbolic link of the file watertype_fvgcm2x2.5 at ./mlo/ics_bcs. e). goto ./mlo/ics_bcs/levitus, run cnvt_mldpd_fvgcm2x2.5.f, cnvt_salt.sh, and cnvt_temp.sh to create initial conditions (mixed layer depth, temperature and salinity profiles) based on Levitus 94 Wrold Atlas. please remeber to change the vertical gird in cnvt_salt.sh and cnvt_temp.sh to be consistent with ./mlo/code/mlo.h. Make symbolic links of the resulting files at ./mlo/ics_bcs. 4. check ./mlo/runmlo_qsfcor.sh to understand how to run the model in a temporary directory. This script will create the heat and water flux correction terms, and prodouce balanced initial conditions for future runs. runmlo_qadj.sh performs a hindcast, and if desired, further adjusts the heat and water flux correction terms to minimize the bias. files needed for fully coupled GCM/MLO models are also created. please read ./mlo/code/driver_fvgcm2x2.5.F to understand how the heat and water flux corrections are determined, and what kind of GCM data are required by the MLO model. For questions and bugs, please contant me. I'd appreciate it if you let me know what you plan to do with this mixed- layer ocean model. Fanglin Yang Environmental Modeling Center National Centers for Environmental Prediction 5200 Auth Road, Camp Springs, MD 20746 Tel: 301-7638000 x7296 E-mail: fanglin.yang@noaa.gov