SEA v3.0: Major updates

This page is intended for those that have used previous versions of SEA and wish to know what differences to expect with version 3.0. Only brief details are given on this page, with in-depth descriptions described in the much updated user guide.

1. Modified QUICK tracer advection scheme (-Dquick):

   • The predict-correct scheme (of Farrow and Stevens, 1995) has been replaced by a revised biharmonic scheme (described by Webb et al., 1998). This one-step scheme is more efficient and is found to be more compatible when used in conjunction with other optional modules.

2. Modified free surface routine:

   • Bug fix: model no longer gains water and the free surface height is conserved (fixed in SEA v2.3).

   • Sequential optimisation: split single i,j loop into three separate i,j loops, for: height field timestepping; barotropic velocity timestepping; free surface averaging.
     => computation time for free surface routine reduced by 20%.

3. Implemented surface forcing module (-Dreal_forcing):

   • Eases prescription of surface boundary conditions and includes all routines to read in and update user-supplied surface forcing data.

   • Data can either be constant (annual means) or periodic (seasonal, monthly, etc.), using a combination of compiler options to indicate which (-Dconstant_sst -Dconstant_sss -Dconstant_ws -Dperiodic_sst -Dperiodic_sss -Dperiodic_ws).

   • For periodic data, all datasets pertaining to one forcing field are contained in a single direct access file (each record representing one period) and a simple linear interpolation scheme is used to vary the forcing values between periods.

   • In parallel mode files are split into sub-files, for which a utility program is provided (pre-data).

4. Modified pre and post processing utilities:

   • Routines changed to deal in 2-D horizontal slabs, rather than the elaborate scheme to deal with east-west slabs. This greatly simplifies their coding and readability.

   • The post processing utility (utils/post-sea.F) for restart and snapshot (sub-)files is much simpler to use and offers greater functionality (with 8 options). There is no longer the need to re-compile to convert model sub-files to either HDF or UFM. Can also convert HDF-2-UFM and UFM-2-HDF directly.

   • The pre processing utility for restart files (utils/pre-sea.F) complements above post processing utility (with 2 options).

   • The template program utils/pre-data.F has been split into two fully-functional utilities pre-data.F and pre-init.F. The former is responsible for pre processing 2-D surface forcing datasets, whilst the latter caters for 3-D initial datasets.

   • Cray T3D/T3E binary conversion options have been added for greater portability of data files (instantiated by -Dcray option).

5. Compiler directives renamed/removed:

   • -Dcray replaces the -Dcray_t3d compiler directive and the model code has been modified to cater for Cray T3E architectures as well as Cray T3D.

   • -Dreal4 notifies the model that single precision floating point variables are being used, replacing the -Ddouple_p directive. Hence real*8 is now the assumed default.

   • -Drec_bytes is no longer an option. Instead, bytes are used to calculate record lengths and for those architectures that assume otherwise other compiler options must be specified (eg. on DEC Alphas "-assume byterecl").

6. Directory restructure:

   • The topogs/ directory has been removed and the topography dataset is stored in the data/ directory instead, as topog_kmt.

   • To ease file congestion, an extra sub-directory level has been added to the sub-directories restarts/, snaps/ and data/. This model sub-directory is used to store current model sub-files of the datasets stored in the parent sub-directories.

     restarts/       .. archived restarts (eg. r000000.hdf or r000000.ufm)
     restarts/model/ .. model restart sub-files (eg. r000000.#)
     snaps/          .. archived snapshots (eg. s000000.hdf or s000000.ufm)
     snaps/model/    .. model snapshot sub-files (eg. s000000.#)
     data/           .. model data input (eg. topog_kmt, surface_temp, init_salt)
     data/model/     .. dataset sub-files (eg. topog.#)
     

7. Changes to restart and snapshot filename format:

   • Restart filename format changed from "d999999.#" to "r999999.#". This is more consistent naming strategy ('r' for restarts) and is in readiness for future diagnostic filenames (to be implemented later) which will use 'd' for diagnostics.

   • Variable length number of digits, for day number, when creating names for restart and snapshot files. Requires single modification to "day_lth" only, in include/iounit.h (default is day_lth=6, as above).

8. Changed aspects of run-time parameter file ocean.in:

   • Namelist (re-)introduced for reading run-time parameters.

   • Less ambiguous parameters for the length of a run, with "fnrest" and "days" replaced by "first_day" and "last_day" (and a single timestep is not forced to complete if last_day=first_day).

9. Parallel optimisation:

   • Message passing routines modified to ignore land points when communicating boundary data points, thus reducing message sizes.

   • The sending/receiving of barotropic forcing (necessary for -Dfs_opt) is now tagged on to the sending/receiving of baroclinic velocities. Hence no need for additional messages to be sent. As a result the subroutines SPI_Send_2d_Z and SPI_Recv_2d_Z have therefore been merged into SPI_Send_3d_UV and SPI_Recv_3d_UV respectively.

   • Added "ionum" to variable to ocean.in parameter file, to indicate the number of tokens to use when synchronising parallel I/O. This is used to prevent a mass free-for-all (ionum=0) when performing parallel I/O. I/O can be completely sequential (one process at a time) when ionum=1, or various levels of concurrency are permitted when ionum>1.

   • -Dno_spawn added for PVM implementations that don't require explicit spawning of parallel processes (such as the Cray T3D/T3E). This is a subset of the -Dcray option, but other architectures may also require it.

10. Miscellaneous changes and additions

    • -Ddebug_it option implemented, which identifies subroutines as they are entered and exited, to aid debugging (but not particularly useful at this stage !!!!).

    • -Ddiags_xtra option implemented, which outputs additional information with the timestep diagnostics (average height, temperature and avergae salinity, along with tracer variances).

    • Masks changed from integers to reals, hence int->real conversion is not necessary in model calculations.

    • Bug in Kraus-Turner mixed layer module (-kraust) reported and fixed.

    • Removed CPU timing from timestep diagnostics line, as not particularly useful and not very portable.

    • Added -Dinit_tracers option to cater for the those wishing to start a model run using a specific set of tracer values (complemented by pre-init utility described above).