Highlights of changes to the NCAR CSM ocean model (NCOM) since the release of NCOM 1.2 in August, 1996 include:
For a brief description of changes to NCOM 1.2 files, see the section
During the restructuring of NCOM to allow diagnostics timesteps to
be multitasked (see below), some multitasking errors in diagnostic
quantities were introduced into the code. These errors have been
corrected, except that a known bug in the
diagnosis of the maximum Courant number will be corrected at a later
date.
Other NCOM 1.3 errors which arose when the flux-coupler controlled
the creation of NCOM history files have also been corrected.
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NCOM I/O has been redesigned in order to minimize traffic on the
NCAR mass-storage system (MSS), to allow for more system-efficient model
restarts, and to accomodate new namelist input required by
the newly released flux coupler. Also, a new C preprocessor
I/O option, "NOMSS,"
has been added to manage file I/O without the NCAR MSS.
The restart "pointer" file, whose name is set in the variable
"rest_pfile", is no longer written to the MSS. Instead, it is
written to the user's home directory ($RPTDIR/ocn.$CASE.rpointer in the
coupled-model and $HOME/ocn.$case.$cexpnam.rpointer in the stand-alone model)
at specified model times (see restart options below).
The pointer file has a new format; one important feature is that
all restart ("R2", "R3", etc. ) files
associated with the model restart time are explicitly listed.
The restart files are still written to the NCAR MSS, or,
under the "NOMSS" option, are moved to a specified disk location,
but now copies of the most recent restart files are also available
in the execution directory, allowing the model to by-pass the
MSS at the time of a model restart.
New time-manager options have also been added, allowing the user greater
flexibility
in the selection of those model times when history and restart files are
created and diagnostics are printed.
For many applications, the "write_at_eoy"
option is desirable, in order to minimize the number of files
generated by NCOM. The new write_at_xxx options are set in
namelist "contrl".
New options have been added to namelist "fileinf" to control
NCAR mass-storage options, and character lengths have been extended
for croot and cexpnam:
Because timeseries information is included in the "H4" history
file, the H4 file is now created even when the C preprocessor option
time_average is selected in conjunction with one of the
"write_at_eom" or "write_at_eoy" options.
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A new message-passing protocol has been implemented in each of the
CSM component models and the flux coupler. Most recently, all
models communicated via the NCAR SCD message-passing software MCL;
presently, all models use a locally modified version of MPI.
Several small, and mainly internal, changes were implemented in
NCOM concurrently with the modified MPI. For
instance, the NCOM 1.2 user will note that the file msg_mcl.F has
been replaced with the more generically named msg.F, and a
"wrapper" subroutine has further isolated all message-passing
references, thus simplifying the task of any future
message-passing changes. Subroutines with specific
message-passing references in their names have been
renamed with more generic names.
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Minor modifications were necessary to several subroutines in order to
conform with F90 requirements. More substantial changes were necessary
to compensate for Cray F90 optimization features which
caused results to vary in the lowest bits when the multitasked model was run
on different numbers of processors. In order to eliminate the optimization
errors, computations were rearranged in files clinic.F, hrzdiv.F,
isopyc.F, tracer.F, fdifm.h, and fdift.h.
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The surface flux subroutine, sflx, has been substantially
restructured to improve its modularity and to permit the
active ocean model to be coupled with climatological versions of the ice
and atmosphere models. This allows for a "coupled
stand-alone" ocean model which has the
same options as the fully stand-alone ocean model,
but with atmospheric-model fluxes provided to force the ocean model.
Another modification allows for active ocean and ice models to be
coupled with a climatological atmospheric model.
Presently, these particular climatological component models are under
development and are not yet publicly available; thus, the two new C
preprocessor options, coupled_ocean_only and
coupled_ocean_ice, are not publicly supported by the NCOM
developers at this time.
In order to make the stand-alone and "coupled stand-alone" versions
consistent, marginal seas are identified in both versions with the
region number 7 ; all versions of the ocean model now use the same regionmask.
The treatment of marginal seas may change again in the
future, after the treatment of river run-off from the CSM land model is
finalized in the NCOM.
Users should note that the re-ordering of model computations in the sflx subroutines
causes slight numerical differences between the NCOM 1.2 and NCOM 1.3
results.
The diagnostics subroutines diag and diag2 were also
rewritten. Subroutine step is no longer required to be
single-threaded whenever the present timestep is a diagnostic or
time-averaging timestep, which results in improved multitasked model
performance.
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In addition to the more substantial changes to NCOM noted above,
there have been several smaller changes and corrections made to the
code, as well.
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All NCOM 1.2 job scripts are incompatible with NCOM 1.3 because of
code and message-passing changes. Users who have customized
their NCOM 1.2 job scripts are encouraged to incorporate their
changes into the newly released NCOM 1.3 job scripts, instead of
vice versa .
The coupled ocean model setup script, ocn.setup.csh, has
been altered in several ways. First, the MPI message-passing library
is now loaded, replacing MCL libraries. Second, the script now
more closely resembles the setup scripts in the other component
models, with the most significant change being the use of Makefile
to generate the ocean-model binary. Finally, the script
create_2x2_ocn_binary.csh has been renamed setdefs.csh,
and its functionality has been reduced to setting the C preprocessor
options only.
The stand-alone ocean job scripts (stand-alone_2x2.script
and stand-alone_3x3.script) have been renamed stand-alone.csh
, and each resides in its own resolution-dependent subdirectory
(although this may
be slightly revised in the near future). The stand-alone scripts
have also been restructured to more closely resemble the
coupled-model script: stand-alone.csh now calls
setdefs_sa.csh (which sets the stand-alone model's
C preprocessor options) and also uses a Makefile to create the
ocean binary, ocn (formerly ocean).
All references to prec_factor and the file "precipf" have
been eliminated in the stand-alone job script; instead, a default
value for the precipitation factor is set in block data blkdta,
and the user may, if desired, set an override in namelist eddy.
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This page is maintained by Nancy Norton
( njn01@ncar.ucar.edu )
Last modified on September 5, 1997.
Corrections and changes (September 5, 1997)
New Model I/O
The write_at_eom and write_at_eoy sub-options can be
selected in any combination, or, if all eom or eoy sub-options are
desired, then it is sufficient to select write_at_eom or write_at_eoy
option only. Any conflict in eoy/eom options or sub-options is resolved
in subroutine checks in favor of the end-of-year version.
NOTE :
Presently, in order for all history-file quantities
to be computed correctly, both the write_at_eoX_history
and write_at_eoX_diagnostics options must be true at the
same model timestep. Subroutine tmngr has been
modified to combine the two options until the NCOM
has been reworked to allow these options to be decoupled.
(September 5, 1997)
New Message Passing for Coupled-Model Integrations
Fortran 90 Compatibility
Restructured Surface-Flux and Diagnostics Subroutines
Minor Corrections and Miscellaneous Changes
New Job Scripts with Makefile
Brief File-by-File Description of NCOM Code Modifications
(September 5, 1997)
(September 5, 1997)
(September 5, 1997)
(September 5, 1997)
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(September 5, 1997)