The CAS Atmospheric Forcing Data Set
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PURPOSE:  For driving land surface models such as the Community Land Model (CLM) in an offline mode

DATA PERIOD: 1 January 1948 – 31 December 2004

 

DATA RESOLUTION: 8 times daily: 1.5Z, 4.5Z, 7.5Z, 10.5Z, 13.5Z, 16.5Z, 19.5Z

 

DATA LOCATION: On NCAR MSS in directory /ADAI/TQIAN/LSMF/NCEPDATA/

 

DATA FILES: in netCDF format as yyyy-mm.nc, where yyyy is the 4-digit year, mm is the 2-digit month, each file has about 107 MB.

DATA GRID:   Global - T62 Gaussian (192 x 94)(invalid data over oceans)

LEVELS: Surface or near the surface

CONSTRUCTION METHOD: Observed monthly precipitation, surface air temperature, cloud cover and recent satellite solar radiation were used to adjust the NCEP/NCAR 6-hourly reanalysis data. See Qian et al. for details.

 

REFERENCE:  

Qian, T., A. Dai, K. E. Trenberth, and K. W. Oleson, 2006: Simulation of global land surface conditions from 1948-2004. Part I: Forcing data and evaluation.  J. Hydrometeorology, 7,953-975. (Qian_etal_JHM06.pdf)

 

CONTACTS: Dr. Keith Oleson <olsen@ucar.edu> or Dr. Aiguo Dai <adai@ucar.edu>

 


FIELDS: Description                       Name      Units   Levels   Notes
------------------------------------------------------------------------------
        Air Temperature                   TBOT      K       2 m      instantaneous
        Specific Humidity                 QBOT      kg/kg   2 m      instantaneous
        Wind Speed                        WIND      m/s     10 m     instantaneous
        Surface Pressure                  PSRF      Pa      surface  instantaneous
        Precipitation                     PRECTmms  mm/s    surface  6-hr ave.
        Surface Downward Solar Radiation  FSDS      W/m2    surface  6-hr ave.
-------------------------------------------------------------------------------

Note:   For state variables (TBOT, QBOT, WIND, PSRF), they represent the
        instantaneous values at the specified time.
        For precipitation and downward solar (PRECTmms and FSDS),
        they represent the averages over the 6-hour period, i.e.,
        values at 1.5Z and 4.5Z both represent 00Z-06Z average, values at 7.5Z
        and 10.5Z both represent 06Z-12Z average, etc..
        In CLM, the values at 1.5Z provide the forcing for 00Z-03Z, 4.5Z for
        03Z-06Z, etc.



HOW TO OBTAIN THE DATA (1948-01.nc to 2004-12.nc)

  1. Obtain the full data set(~72GB) online from: the Earth System Grid (under CLM3.5/4.0 Input Data). You may need to apply for an account from the ESG group.
  2. Copy the files from the NCAR Mass Storage System (MSS) from an NCAR computer:
    1. Login to an NCAR computer.
    2. Read it from the MSS
      • msrcp MSS:/ADAI/TQIAN/LSMF/NCEPDATA/1948-01.nc . &

     

     

    USAGES:
    Please check CLM3.0 User's Guide
    http://www.cgd.ucar.edu/tss/clm/distribution/clm3.0/UsersGuide/UsersGuide/node11.html


    9.1 EXAMPLE 1: OFFLINE INITIAL RUN, ONE DAY, GLOBAL
    When the model is run in offline mode using a pre-existing surface
    dataset, the minimum namelist parameters are: CASEID, NSREST, NESTEP or
    NELAPSE, FSURDAT, FPFTCON, OFFLINE_ATMDIR, START_YMD, and DTIME. If
    FSURDAT is blank, a surface dataset will be generated at run time and
    additional variables need to be specified (see section 4.2 and Examples 5
    and 6). Namelist parameters not specified will be set to default values.
    The following gives an example of a simple namelist.

     &clmexp
     CASEID         =  'test01'
     NSREST         =   0
     NESTEP         =  -1
     FSURDAT        =  '$CSMDATA/srfdata/clms_64x128_USGS_c030605.nc'
     FINIDAT        =  ' '
     FPFTCON        =  '$CSMDATA/pftdata/pft-physiology'
     FRIVINP_RTM    =  '$CSMDATA/rtmdata/rdirc.05'
     OFFLINE_ATMDIR =  '$CSMDATA/NCEPDATA'
     START_YMD      =  19971231
     DTIME          =  1800
     HIST_NHTFRQ    =  -24
     /

    CASEID = 'test01'
    Case identifier which distinguishes this particular simulation from
    another. The string in CASEID shows up in the names of history, restart,
    and initial files, in the restart pointer file name (see Example 2) and
    in the Mass Store pathname where history, restart, and initial files are
    placed if the Mass Store is used.


    NSREST = 0
    Requests an initial run, as opposed to a restart or a branch run. An
    initial run does not require the use of an initial input datafile
    (FINIDAT). If none is provided, the model uses non spun-up initialization
    provided in the code (see src/main/iniTimeVar.F90).


    NESTEP = -1
    Specifies the run's ending time to be at the end of day 1.


    FSURDAT = '$CSMDATA/srfdata/clms_64x128_USGS_c030605.nc'
    Specifies the name of the surface data input file. This particular T42
    surface dataset can be used both in cam and offline mode. The model
    resolution (i.e. parameters LSMLON and LSMLAT) must be compatible with
    the resolution of FSURDAT. If the filename appeared without a path
    specifying its exact location, the file would be expected in the
    executable directory, defined by the environment variable $MODEL_EXEDIR.


    FINIDAT = ' '
    Specifies the initial file to be used to prescribe initial values for
    time-dependent variables. Since no file is specified in this case, the
    model will be internally initialized to non spun-up values (arbitrary
    initialization).


    FPFTCON = '$CSMDATA/pftdata/pft-physiology'
    Specifies a file with PFT (Plant Functional Type) parameters.


    FRIVINP_RTM = '$CSMDATA/rtmdata/rdirc.05'
    Specifies the input file required for the operation of RTM (River
    Transport Model). By default, RTM will operate at half degree horizontal
    resolution and will be invoked every 3 hours, where the fluxes input to
    RTM (i.e., runoff) are averaged over the 3 hour period. If the user wants
    the RTM scheme to operate at a different frequency than once every 3
    hours, RTM_NSTEPS should be set to the desired value of timesteps. Use of
    RTM is activated in the jobscript.csh with the C pre-processor (cpp)
    directive #define RTM in the header file preproc.h (see section 3.1.3).


    OFFLINE_ATMDIR = '$CSMDATA/NCEPDATA'
    Specifies the location of the atmospheric driver data set. Such a data
    set is required for the model to run in offline mode.


    START_YMD = 19971231
    Specifies the base date of the simulation and must be compatible with the
    atmospheric input data. For example, START_YMD = 19971231 will use the
    atmospheric input file 1997-12.nc. In a restart or branch run, START_YMD
    need not be changed, as long as it refers to a date earlier than the date
    of restart or branch.


    DTIME = 1800
    Specifies the simulation's timestep in seconds. In offline mode, the
    model can handle a timestep of up to 3600 seconds.


    HIST_NHTFRQ = -24
    Primary history files and restart files will be produced in the
    executable directory and will be written every 24 hours.

     

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    Taotao Qian: tqian@ucar.edu