Forcing ocean and sea ice components
Runs with active ocean and sea ice components that are forced with prescribed atmospheric fluxes can be customized by editing the data atmosphere namelist and streams files.
Note
The data atmosphere fields can come from any source as long as they contain the requisite forcing fields. The easiest way to generate a “correct” set of atmospheric forcing fields is to use coupler history files from a CESM run in which CAM is active, but forcing from other reanalyses and data products such as JRA-55 and GISS are also acceptable.
The CIME documentation does contain instructions for configuring data atmosphere files. However, the instructions contained in that document are vague:
“Edit the user_datm.streams.txt.* file.”
Setting up a case to get acquainted with the files
Setting up a G
compset case is the simplest way to become familiar with the
data atmosphere stream files (datm.streams*
).
cd <cesm_root>/cime/scripts/
./create_newcase --case /glade/work/${USER}/cases/G.fosi.f09_g17.001 --compset G --res f09_g17 --project PXXXXXXXX --run-unsupported
cd /glade/work/${USER}/cases/G.fosi.f09_g17.001
./case.setup
./preview_namelists
The preview_namelists
script will fill the CaseDocs
with the namelist
and data streams files necessary to build a forced ocean/sea ice (FOSI) run.
ls CaseDocs/
atm_modelio.nml datm.streams.txt.presaero.clim_2000 ice_in seq_maps.rc
cpl_modelio.nml drof_in ice_modelio.nml wav_in
datm_in drof.streams.txt.rof.diatren_ann_rx1 lnd_modelio.nml wav_modelio.nml
datm.streams.txt.CORE2_NYF.GISS drv_in ocn_modelio.nml
datm.streams.txt.CORE2_NYF.GXGXS esp_modelio.nml pop_in
datm.streams.txt.CORE2_NYF.NCEP glc_modelio.nml rof_modelio.nml
There are four datm.streams*
files. They contain a lists of all of the
forcing fields from coupler history files that are necessary to conduct a FOSI
run.
Structure of a data atmosphere stream file
The data atmosphere stream files are XML files that specify a domain file, a variable file and a time offset.
vim CaseDocs/datm.streams.txt.CORE2_NYF.GISS
These are the XML nodes in a datm.streams*
file:
<?xml version="1.0"?>
<file id="stream" version="1.0">
<dataSource>
GENERIC
</dataSource>
<domainInfo>
<variableNames>
time time
lon lon
lat lat
area area
mask mask
</variableNames>
<filePath>
/glade/p/cesmdata/cseg/inputdata/atm/datm7/NYF
</filePath>
<fileNames>
nyf.giss.T62.051007.nc
</fileNames>
</domainInfo>
<fieldInfo>
<variableNames>
lwdn lwdn
swdn swdn
swup swup
</variableNames>
<filePath>
/glade/p/cesmdata/cseg/inputdata/atm/datm7/NYF
</filePath>
<fileNames>
nyf.giss.T62.051007.nc
</fileNames>
<offset>
0
</offset>
</fieldInfo>
</file>
The dataSource
node typically specifies where the data come from. While
this GISS file merely says GENERIC
, the dataSource node from the CAM6
reanalysis is more descriptive, CAM6-DART Ensemble Reanalysis (NCAR
RDA ds345.0)
.
The domainInfo
node specifies a netCDF domain file and the variables it
contains, time
, lon
, lat
, area
, mask
. In this example, the
forcing fields are specified on the T62
spectral grid.
The fieldInfo
node specifies a netCDF variable file and the variables it
contains. There are two strings in the variableNames
entry because the
data source might name a field differently than what the coupler is expecting.
For example, in CaseDocs/datm.streams.txt.CORE2_NYF.GXGXS
, the
precipitation variable is declared in this manner:
<variableNames>
prc prec
</variableNames>
The pair of strings translate between the variable key in the GXGXS source file
(Large and Yeager, 2004) 1 which specifies this field as prc
and the
key expected by the coupler, which is prec
.
Time offset and axis mode
The time offset, offset
, and time axis mode, taxmode
, are the trickiest
aspects of the datm.streams*
files to get right.
The best explanation of these settings is in the CLM Customizing the DATM namelist documentation.
Specified fields
These are the fields that should be specified for a FOSI run:
lwdn
downwelling longwave radiationswdn
downwelling shortwave radiationswup
upwelling shortwave radiationprec
precipitationdens
densitypslv
sea level pressureshum
specific humiditytbot
10-meter temperatureu
10-meter zonal velocityv
10-meter meridional velocity
References
- 1
Large, W. G., and S. G. Yeager, 2004: Diurnal to decadal global forcing for ocean and sea-ice models: The data sets and flux climatologies. NCAR Tech. Note NCAR/TN-460+STR, 111 pp.