The CAS Atmospheric Forcing Dataset

PURPOSE: For driving land-surface models such as the Community Land Model (CLM) in an offline mode

DATA PERIOD: 1 Jan 1948 - 21 Dec 2004

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

DATA LOCATION: On NCAR MSS: /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 (192x94); invalid data over oceans.

LEVELS: Surface or near surface

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

FIELDS:

Description Name Units Levels Notes
Air temperature TBOT K 2 m instantaneous
Specific humidity QBOT kg kg-1 2 m instantaneous
Wind speed WIND m s-1 10 m instantaneous
Surface pressure PSRF Pa surface instantaneous
Precipitation PRECTmms mm s-1 surface 6 hour average
Surface downward solar radiation FSDS W m-2 surface 6 hour average

Note: State variables (TBOT, QBOT, WIND, PSRF) are the instantaneous values at the specified time. Precipitation and downward solar radiation (PRECT, FSDS) are the averages over the 6 hour period (i.e. values at 1.5Z and 4.5Z both represent 00Z-06Z averages, 7.5Z and 10.5Z represent 06Z-12Z averages, 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:

  • Obtain the full dataset (~72 GB) online from the Earth Systems Grid (ESG). You may need to apply for an account from the ESG group.

  • Internal use: Copy the files from the NCAR MSS from an NCAR computer
    • Login to an NCAR computer
    • Read the data via the command:
      • msrcp: mss:/ADAI/TQIAN/LSMF/NCEPDATA/1948-01.nc .
    • Repeat until all files have been retrieved.

USAGES: Please check CLM3.0's User's Guide.


References:

  • 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. [pdf]

Please contact Dr. Aiguo Dai or Dr. Keith Oleson


9.1 Example 1: Offline initial run, one day, global

When the model is run in offline mode using a pre-exisiting 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 distringuishes this particular simluation 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 MSS pathname where history, restart and initial files are placed if the MSS is used

NSREST = 0

  • Requests an initial run, as opposed to a restart or brand 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 is expected to be in the executable directory, defined by the environment variable $MODEL_EXEDIR

FINIDAT = ' '

  • Specifies the initial file to prescribe inital values for the 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 at file with plant functional type (PFT) parameters

FRIVINP_RTM = '$CSMDATA/rtmdata/rdirc.05'

  • Specifies the input file required for the operation of the river transport model (RTM). 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, then RTM_NSTEPS should be set to the desired value of times. Use of the 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 dataset. Such a dataset is required for the model to run in offline mode.

START_YMD = 19971231

  • Specifies the base date of the simulation and must be compatable 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 sec.

HIST_NHTFRQ = -24

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