Overview

An input data stream is a time-series of input data files where all the fields in the stream are located in the same data file and all share the same spatial and temporal coordinates (ie. are all on the same grid and share the same time axis). Normally a time axis has a uniform dt, but this is not a requirement.

The data models can have multiple input streams.

The data for one stream may be all in one file or may be spread over several files. For example, 50 years of monthly average data might be contained all in one data file or it might be spread over 50 files, each containing one year of data.

The data models can loop over stream data -- repeatedly cycle over some subset of an input stream's time axis. When looping, the models can only loop over whole years. For example, an input stream might have SST data for years 1950 through 2000, but a model could loop over the data for years 1960 through 1980. A model cannot loop over partial years, for example, from 1950-Feb-10 through 1980-Mar-15.

The input data must be in a netcdf file and the time axis in that file must be CF-1.0 compliant.

There are two main categories of information that the data models need to know about a stream:

• data that describes what a user wants -- what streams to use and how to use them -- things that can be changed by a user.

• data that describes the stream data -- meta-data about the inherent properties of the data itself -- things that cannot be changed by a user.

Stream Data

The strdata (short for "stream data") input is set via a fortran namelist called shr_strdata_nml. That namelist, the strdata datatype, and the methods are contained in the share source code file, models/csm_share/shr/shr_strdata_mod.F90. In general, strdata input defines an array of input streams and operations to perform on those streams. Therefore, many namelist inputs are arrays of character strings. Different variable of the same index are associated. For instance, mapalgo(1) spatial interpolation will be performed between streams(1) and the target domain.

The following namelist are available with the strdata namelist.

Specifying What Streams to Use

The data models have a namelist variable that specifies which input streams to use and, for each input stream, the name of the corresponding stream description file, what years of data to use, and how to align the input stream time axis with the model run time axis. This input is set in the strdata namelist input.

General format:

   &shr_strdata_nml
      streams = 'stream1.txt year_align year_first year_last ',
                'stream2.txt year_align year_first year_last ',
                ...
                'streamN.txt year_align year_first year_last '
   /

where:

The stream text files for a given data model mode are automatically generated by the corresponding data model build-namelist with present names. As an example we refer to the following datm_atm_in example file (that would appear in both $CASEROOT/CaseDocs and $RUNDIR):

 datamode   = 'CLMNCEP'
 domainfile = '/glade/proj3/cseg/inputdata/share/domains/domain.lnd.fv1.9x2.5_gx1v6.090206.nc'
 dtlimit    = 1.5,1.5,1.5,1.5
 fillalgo   = 'nn','nn','nn','nn'
 fillmask   = 'nomask','nomask','nomask','nomask'
 mapalgo    = 'bilinear','bilinear','bilinear','bilinear'
 mapmask    = 'nomask','nomask','nomask','nomask'
 streams    = "datm.streams.txt.CLM_QIAN.Solar  1895 1948 1972  ", 
              "datm.streams.txt.CLM_QIAN.Precip 1895 1948 1972  ",
              "datm.streams.txt.CLM_QIAN.TPQW   1895 1948 1972  ", 
              "datm.streams.txt.presaero.trans_1850-2000 1849 1849 2006"
 taxmode    = 'cycle','cycle','cycle','cycle'
 tintalgo   = 'coszen','nearest','linear','linear'
 vectors    = 'null'

As is discussed in the CESM1.1 User's Guide, to change the contents of datm_atm_in, you can edit $CASEROOT/user_nl_datm to change any of the above settings EXCEPT FOR THE NAMES datm.streams.txt.CLM_QIAN.Solar, datm.streams.txt.CLM_QIAN.Precip, datm.streams.txt.CLM_QIAN.TPQW and datm.streams.txt.presaero.trans_1850-2000. Note that any namelist variable from shr_strdata_nml and datm_nml can be modified by adding the appropriate keyword/value pairs to user_nl_datm. As an example, the following could be the contents of $CASEROOT/user_nl_datm:

!------------------------------------------------------------------------
! Users should ONLY USE user_nl_datm to change namelists variables
! Users should add all user specific namelist changes below in the form of 
! namelist_var = new_namelist_value 
! Note that any namelist variable from shr_strdata_nml and datm_nml can 
! be modified below using the above syntax 
! User preview_namelists to view (not modify) the output namelist in the
! directory $CASEROOT/CaseDocs
! To modify the contents of a stream txt file, first use preview_namelists
! to obtain the contents of the stream txt files in CaseDocs, and then
! place a copy of the  modified stream txt file in $CASEROOT with the string 
! user_ prepended. 
!------------------------------------------------------------------------
 streams    = "datm.streams.txt.CLM_QIAN.Solar  1895 1948 1900  ", 
              "datm.streams.txt.CLM_QIAN.Precip 1895 1948 1900  ",
              "datm.streams.txt.CLM_QIAN.TPQW   1895 1948 1900  ", 
              "datm.streams.txt.presaero.trans_1850-2000 1849 1849 2006"

and the contents of shr_strdata_nml (in both $CASEROOT/CaseDocs and $RUNDIR) would be

 datamode   = 'CLMNCEP'
 domainfile = '/glade/proj3/cseg/inputdata/share/domains/domain.lnd.fv1.9x2.5_gx1v6.090206.nc'
 dtlimit    = 1.5,1.5,1.5,1.5
 fillalgo   = 'nn','nn','nn','nn'
 fillmask   = 'nomask','nomask','nomask','nomask'
 mapalgo    = 'bilinear','bilinear','bilinear','bilinear'
 mapmask    = 'nomask','nomask','nomask','nomask'
 streams    = "datm.streams.txt.CLM_QIAN.Solar  1895 1948 1900  ", 
              "datm.streams.txt.CLM_QIAN.Precip 1895 1948 1900  ",
              "datm.streams.txt.CLM_QIAN.TPQW   1895 1948 1900  ", 
              "datm.streams.txt.presaero.trans_1850-2000 1849 1849 2006"
 taxmode    = 'cycle','cycle','cycle','cycle'
 tintalgo   = 'coszen','nearest','linear','linear'
 vectors    = 'null'

As is discussed in the User's Guide, you should use preview_namelists to view (not modify) the output namelist in CaseDocs.

Stream Description File

The stream description file is not a Fortran namelist, but a locally built xml-like parsing implementation. Sometimes it is called a "stream dot-text file" because it has a ".txt." in the filename. Stream description files contain data that specifies the names of the fields in the stream, the names of the input data files, and the file system directory where the data files are located. In addition, a few other options are available such as the time axis offset parameter.

In CESM1.1, each data model's build-namelist utility (e.g. models/atm/datm/bld/build-namelist) automatically generates these stream description files. The directory contents of each data model will look like the following (using DATM as an example)

models/atm/datm/bld/build-namelist
models/atm/datm/bld/namelist_files/namelist_definition_datm.xml
models/atm/datm/bld/namelist_files/namelist_defaults_datm.xml

The namelist_definition_datm.xml file defines all the namelist variables and associated groups. The namelist_defaults_datm.xml provides the out of the box settings for the target data model and target stream. build-namelist utilizes these two files to construct the stream files for the given compset settings. You can modify the generated stream files for your particular needs by doing the following:

1. Call setup OR preview_namelists.

2. Copy the relevant description file from $CASEROOT/CaseDocs to $CASEROOT and pre-pend a "user_" string to the filename. Change the permission of the file to write. For example, assuming you are in $CASEROOT

   cp CaseDocs/datm.streams.txt.CLM_QIAN.Solar user_datm.streams.txt.CLM_QIAN.Solar chmod u+w user_datm.streams.txt.CLM_QIAN.Solar

3. • Edit user_datm.streams.txt.CLM_QIAN.Solar with your desired changes.
   • Be sure not to put any tab characters in the file: use spaces instead.
   • In contrast to other user_nl_xxx files, be sure to set all relevant data model settings in the xml files, issue the preview_namelist command and THEN edit the user_datm.streams.txt.CLM_QIAN.Solar file.
   • Once you have created a user_xxx.streams.txt.* file, further modifications to the relevant data model settings in the xml files will be ignored.
   • If you later realize that you need to change some settings in an xml file, you should remove the user_xxx.streams.txt.* file(s), make the modifications in the xml file, rerun preview_namelists, and then reintroduce your modifications into a new user_xxx.streams.txt.* stream file(s).

4. Call preview_namelists

5. Verify that your changes do indeed appear in the resultant stream description file appear in CaseDocs/datm.streams.txt.CLM_QIAN.Solar. These changes will also appear in $RUNDIR/datm.streams.txt.CLM_QIAN.Solar.

The data elements found in the stream description file are: