3. Input Streams

3.1. 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 – i.e., 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.

Generally, information about what streams a user wants to use and how to use them is input via the strdata (“stream data”) Fortran namelist, while meta-data that describes the stream data itself is found in an xml-like text file called a “stream description file.”

3.2. Stream Data and shr_strdata_nml namelists

The stream data (referred to as strdata) input is set via a Fortran namelist called shr_strdata_nml. That namelist, the associated strdata datatype, and the methods are contained in the share source code file, 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 variables of the same index are associated. For instance, mapalgo(1) spatial interpolation will be performed between streams(1) and the target domain.

Each data model has an associated input namelist file, xxx_in, where xxx=[datm,dlnd,dice,docn,drof,dwav].

The input namelist file for each data model has a stream dependent namelist group, shr_strdata_nml, and a stream independent namelist group. The shr_strdata_nml namelist variables are the same for all data models.


Namelist Groups


datm_nml, shr_strdata_nml


dice_nml, shr_strdata_nml


dlnd_nml, shr_strdata_nml


docn_nml, shr_strdata_nml


drof_nml, shr_strdata_nml


dwav_nml, shr_strdata_nml

The following table summaries the shr_strdata_nml entries.




component specific mode.

Each CIME data model has its own datamode values as described below:

datm dataMode

dice dataMode

dlnd dataMode

docn dataMode

drof dataMode

dwav dataMode


component domain (all streams will be mapped to this domain).

Spatial gridfile associated with the strdata. grid information will be read from this file and that grid will serve as the target grid for all input data for this strdata input. If the value is null then the domain of the first stream will be used as the component domain



character array (up to 30 elements) of input stream filenames and associated years of data.

Each array entry consists of a stream_input_filename year_align year_first year_last. The stream_input_filename is a stream text input file and the format and options are described elsewhere. The year_align, year_first, and year_last provide information about the time axis of the file and how to relate the input time axis to the model time axis.



array (up to 30 elements) of fill algorithms associated with the array of streams.

Valid options are just copy (ie. no fill), special value, nearest neighbor, nearest neighbor in “i” direction, or nearest neighbor in “j” direction.

valid values: ‘copy’,’spval’,’nn’,’nnoni’,’nnonj’

default value=’nn’


array (up to 30 elements) of fill masks.

valid values: “nomask,srcmask,dstmask,bothmask”



array (up to 30 elements) fill mapping files to read. Secifies the weights file to read in instead of computing the weights on the fly for the fill operation. If this is set, fillalgo and fillmask are ignored.



array of fill mapping file to write



array of spatial interpolation algorithms



array of spatial interpolation mask



array of spatial interpolation mapping files to read (optional)



array (up to 30 elements) of spatial interpolation mapping files to write (optional). Specifies the weights file to generate after weights are computed on the fly for the mapping (interpolation) operation, thereby allowing users to save and reuse a set of weights later. default=’NOT_SET’


array (up to 30 elements) of time interpolation algorithm options associated with the array of streams.

valid values: lower,upper,nearest,linear,coszen lower = Use lower time-value

upper = Use upper time-value

nearest = Use the nearest time-value

linear = Linearly interpolate between the two time-values

coszen = Scale according to the cosine of the solar zenith angle (for solar)



array (up to 30 elements) of time interpolation modes.

Time axis interpolation modes are associated with the array of streams for handling data outside the specified stream time axis.

Valid options are to cycle the data based on the first, last, and align settings associated with the stream dataset, to extend the first and last valid value indefinitely, or to limit the interpolated data to fall only between the least and greatest valid value of the time array.

valid values: cycle,extend,limit

extend = extrapolate before and after the period by using the first or last value.

cycle = cycle between the range of data

limit = restrict to the period for which the data is valid



array (up to 30 elements) of setting delta time axis limit.

Specifies delta time ratio limits placed on the time interpolation associated with the array of streams. Causes the model to stop if the ratio of the running maximum delta time divided by the minimum delta time is greater than the dtlimit for that stream. For instance, with daily data, the delta time should be exactly one day throughout the dataset and the computed maximum divided by minimum delta time should always be 1.0. For monthly data, the delta time should be between 28 and 31 days and the maximum ratio should be about 1.1. The running value of the delta time is computed as data is read and any wraparound or cycling is also included. this input helps trap missing data or errors in cycling. to turn off trapping, set the value to 1.0e30 or something similar.



paired vector field names

shr_strdata_nml contains a namelist variable, streams, that specifies a list of input stream description files and for each file what years of data to use, and how to align the input stream time axis with the model run time axis.

The general input format for the streams namelist variable is:

  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 '


   the stream description file, a plain text file containing details about the input stream (see below)
   the first year of data that will be used
   the last year of data that will be used
   a model year that will be aligned with data for year_first

3.3. Details on year_align

The year_align value gives the simulation year corresponding to year_first. A common usage is to set this to the year of RUN_STARTDATE. With this setting, the forcing in the first year of the run will be the forcing of year year_first. Another use case is to align the calendar of transient forcing with the model calendar. For example, setting year_align = year_first will lead to the forcing calendar being the same as the model calendar. The forcing for a given model year would be the forcing of the same year. This would be appropriate in transient runs where the model calendar is setup to span the same year range as the forcing data.

For some data model modes, year_align can be set via an xml variable whose name ends with YR_ALIGN (there are a few such xml variables, each pertaining to a particular data model mode).

An example of this is land-only historical simulations in which we run the model for 1850 to 2010 using atmospheric forcing data that is only available for 1901 to 2010. In this case, we want to run the model for years 1850 (so RUN_STARTDATE has year 1850) through 1900 by looping over the forcing data for 1901-1920, and then run the model for years 1901-2010 using the forcing data from 1901-2010. To do this, we initially set:

./xmlchange DATM_CLMNCEP_YR_ALIGN=1901
./xmlchange DATM_CLMNCEP_YR_START=1901
./xmlchange DATM_CLMNCEP_YR_END=1920

When the model has completed year 1900, then we set:

./xmlchange DATM_CLMNCEP_YR_ALIGN=1901
./xmlchange DATM_CLMNCEP_YR_START=1901
./xmlchange DATM_CLMNCEP_YR_END=2010

With this setup, the correlation between model run year and forcing year looks like this:

RUN   Year : 1850 ... 1860 1861 ... 1870 ... 1880 1881 ... 1890 ... 1900 1901 ... 2010
FORCE Year : 1910 ... 1920 1901 ... 1910 ... 1920 1901 ... 1910 ... 1920 1901 ... 2010

Setting DATM_CLMNCEP_YR_ALIGN to 1901 tells the code that you want to align model year 1901 with forcing data year 1901, and then it calculates what the forcing year should be if the model starts in year 1850.

3.4. Customizing shr_strdata_nml values

The contents of shr_strdata_nml are automatically generated by that data model’s cime_config/buildnml script. These contents are easily customizable for your target experiment. As an example we refer to the following datm_in contents (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 CIME User’s Guide, to change the contents of datm_in, you must edit $CASEROOT/user_nl_datm. In the above example, you can to this to change any of the above settings except for the names


Other than these names, any namelist variable from shr_strdata_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 CIME User’s Guide, you should use preview_namelists to view (not modify) the output namelist in CaseDocs.

3.5. 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.

The data elements found in the stream description file are:


A comment about the source of the data – always set to GENERIC and is there only for backwards compatibility.


Information about the domain data for this stream specified by the following 3 sub elements.


A list of the domain variable names. This is a paired list with the name of the variable in the netCDF file on the left and the name of the corresponding model variable on the right. This data models require five variables in this list. The names of model’s variables (names on the right) must be: “time,” “lon,” “lat,” “area,” and “mask.”


The file system directory where the domain data file is located.


The name of the domain data file. Often the domain data is located in the same file as the field data (above), in which case the name of the domain file could simply be the name of the first field data file. Sometimes the field data files don’t contain the domain data required by the data models, in this case, one new file can be created that contains the required data.


Information about the stream data for this stream specified by the following 3 required sub elements and optional offset element.


A list of the field variable names. This is a paired list with the name of the variable in the netCDF file on the left and the name of the corresponding model variable on the right. This is the list of fields to read in from the data file; there may be other fields in the file which are not read in (i.e., they won’t be used).


The file system directory where the data files are located.


The list of data files to use. If there is more than one file, the files must be in chronological order, that is, the dates in time axis of the first file are before the dates in the time axis of the second file.


The offset allows a user to shift the time axis of a data stream by a fixed and constant number of seconds. For instance, if a data set contains daily average data with timestamps for the data at the end of the day, it might be appropriate to shift the time axis by 12 hours so the data is taken to be at the middle of the day instead of the end of the day. This feature supports only simple shifts in seconds as a way of correcting input data time axes without having to modify the input data time axis manually. This feature does not support more complex shifts such as end of month to mid-month. But in conjunction with the time interpolation methods in the strdata input, hopefully most user needs can be accommodated with the two settings. Note that a positive offset advances the input data time axis forward by that number of seconds.

The data models advance in time discretely. At a given time, they read/derive fields from input files. Those input files have data on a discrete time axis as well. Each data point in the input files is associated with a discrete time (as opposed to a time interval). Depending on whether you pick lower, upper, nearest, linear, or coszen, the data in the input file will be “interpolated” to the time in the model.

The offset shifts the time axis of the input data the given number of seconds. So if the input data is at 0, 3600, 7200, 10800 seconds (hourly) and you set an offset of 1800, then the input data will be set at times 1800, 5400, 9000, and 12600. So a model at time 3600 using linear interpolation would have data at “n=2” with offset of 0 will have data at “n=(2+3)/2” with an offset of 1800. n=2 is the 2nd data in the time list 0, 3600, 7200, 10800 in this example. n=(2+3)/2 is the average of the 2nd and 3rd data in the time list 0, 3600, 7200, 10800. offset can be positive or negative.

Actual example:

      time   time
      lon    lon
      lat    lat
      area   area
      mask   mask
      dn10  dens
      slp_  pslv
      q10   shnum
      t_10  tbot
      u_10  u
      v_10  v

3.6. Customizing stream description files

Each data model’s cime-config/buildnml utility automatically generates the required stream description files for the case. The directory contents of each data model will look like the following (using DATM as an example)


The namelist_definition_datm.xml file defines and sets default values for all the namelist variables and associated groups and also provides out-of-the box settings for the target data model and target stream. buildnml 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. 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 $CASEROOT/CaseDocs/datm.streams.txt.CLM_QIAN.Solar  $CASEROOT/user_datm.streams.txt.CLM_QIAN.Solar
    chmod u+w $CASEROOT/user_datm.streams.txt.CLM_QIAN.Solar
  2. Edit $CASEROOT/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).

  3. Call preview_namelists and 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.