The Community Land Model (CLM) Atmospheric Forcing Data Set
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PURPOSE:  For conducting uncoupled land surface model simulations
FILENAME: yyyy-mm.nc, where yyyy is the 4-digit year, mm is the 2-digit month

FORMAT: netCDF
GRID:   Global - T62 Gaussian (192 x 94)
LEVELS: Surface or near the surface

FIELDS: Description                       Name      Units   Levels   Notes
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	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.

TIMES:  8 times daily: 1.5Z, 4.5Z, 7.5Z, 10.5Z, 13.5Z, 16.5Z, 19.5Z, 21.5Z
        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.
DATES:  January 1948 - December 2002 
SOURCE: NCEP/NCAR 6-hourly reanalysis adjusted by observations

REFERENCES: 
Qian, T., A. Dai, K. E. Trenberth, and K. W. Oleson, 2005: Simulation of global land surface conditions from 1948-2002. Part I: Forcing data and evaluation.  J. Hydrometeorology, submitted.
(http://www.cgd.ucar.edu/cas/adai/publication-dai.html)


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.