The following is a brief outline of the calling sequence for the main CLM2.0 driver routine, driver.F90. A comprehensive outline of the calling sequence for the full CLM2.0 model is provided in the accompanying html document, CLM2.0 Comprehensive Calling Sequence.
The CLM2.0 model can be built to run in one of three modes. It can run
as a stand alone executable where atmospheric forcing data is
periodically read . This will be referred to as offline mode. It can
also be run as part of the Community Atmosphere Model (CAM) where
communication between the atmospheric and land models occurs via
subroutine calls. This will be referred to as cam mode. Finally, it
can be run as a component in a system of geophysical models (CCSM).
In this mode, the atmosphere, land (CLM2), ocean and sea-ice models
are run as separate executables that communicate with each other via
the CCSM flux coupler. This will be referred to as csm mode.
offline mode: The routine, program_off.F90,
provides the program interface for running CLM2.0 in offline
mode. This routine first initializes the CLM2.0 model. Part of this
initialization consists of the the determination of orbital parameters
by a call to the routine shr_orb_params.F90. Subsequently,
the time stepping loop of the model is executed by obtaining
atmospheric forcing and calling the CLM2.0 driver.
csm mode: The routine, program_csm.F90,
provides the program interface for running CLM2.0 in csm mode. In this
mode, orbital parameters are obtained from the flux coupler during
initialization whereas atmospheric data are obtained from the flux
coupler during the time stepping loop.
cam mode: The module, atm_lndMod.F90, contains
the subroutine interfaces necessary to run CLM2.0 in cam mode. The
model is initialized by a call to subroutine atmlnd_ini whereas
subroutine atmlnd_drv is called at every time step by the
CAM atmospheric model to update the land state and return the
necessary states and fluxes back to the atmosphere.
The following presents a brief outline of the routines appearing in the calling sequence for program_off.F90, the main CLM2.0 offline program. Most of the following routines are invoked from the driver routine, driver.F90.
Calculate Earth's orbital parameters.
Calls a series of subroutines (see CLM2.0
Comprehensive Calling Sequence) which
initialize model parameters, read and/or create a surface dataset,
read the initial file (initial simulations only), read the restart
file (restart or branch simulations only). If no initial dataset is
specified in the namelist, the model uses an internal
initialization. If no surface dataset is specified in the namelist,
the model uses a list of raw datasets to create a surface dataset and
read it in.
Read in atmospheric fields and generate atmospheric forcing.
Driver for CLM2.0 physics.
Determine if current time step is the end of history interval.
Determine calender information for next time step.
Determine if two new months of vegetation data need to be read in.
Read monthly vegetation data for two consecutive months.
Calculation of (1) water storage of intercepted precipitation (2)
direct throughfall and canopy drainage of precipitation (3) the
fraction of foliage covered by water and the fraction of foliage that
is dry and transpiring and (4) snow layer initialization if the snow
accumulation exceeds 10 mm.
Determine the fraction of foliage covered by water and the fraction of
foliage that is dry and transpiring.
Main subroutine to determine leaf temperature and surface fluxes based
on ground temperature from previous time step.
Compute saturation mixing ratio and the change in saturation mixing
ratio with respect to temperature.
Compute Visible and NIR solar fluxes absorbed by vegetation and ground
surface. Split canopy absorption into sunlit and shaded
canopy. Calculate NDVI and reflected solar radiation. This routine is
also used for surface radiation for lake biogeophysics.
Compute sensible and latent heat fluxes and their derivatives with
respect to ground temperature using ground temperatures from
previous time step for non-vegetated surfaces or snow-covered
vegetation. Calculate stability and aerodynamic resistances.
Initialize Monin-Obukhov length.
Calculation of the friction velocity and the relation for potential
temperature and humidity profiles of surface boundary layer.
Calculates the leaf temperature, leaf fluxes, transpiration,
photosynthesis and updates the dew accumulation due to
Leaf stomatal resistance and leaf photosynthesis. Uses Ball-Berry
formulation for stomatal conductance, and Farquhar photosynthesis
Provides dimensional and non-dimensional sensible heat conductances
for canopy and soil flux calculations.
Provides dimensional and non-dimensional latent heat conductances for
canopy and soil flux calculations.
Calculates lake temperatures and surface fluxes. Lake temperatures
are determined from a one-dimensional thermal stratification model
based on eddy diffusion concepts to represent vertical mixing of
Determine vegetation phenology
Surface albedos, fluxes (per unit incoming direct and diffuse
radiation) reflected, transmitted, and absorbed by vegetation, and
sunlit fraction of the canopy.
Determine solar declination for next time step.
Determine cosine of solar zenith angle for next time step.
Determine direct and diffuse visible and NIR snow albedos.
Determine soil/lake/glacier/wetland albedos.
Use two-stream approximation to calculate visible and NIR fluxes
absorbed by vegetation, reflected by vegetation, and transmitted
through vegetation for unit incoming direct or diffuse flux given an
underlying surface with known albedo.
Main subroutine to determine soil/snow temperatures including ground
surface temperature and update surface fluxes for new ground
Determine soil/snow temperatures including ground surface
Determine soil/snow thermal conductivity and heat capacity.
Solve tridiagonal system of equations.
Determine phase change within soil/snow layers.
Main subroutine to determine soil/snow hydrology.
Determine the change of snow mass and the snow water.
Determine surface runoff.
Determine infiltration into surface soil layer (minus the
Determine soil moisture.
Determine subsurface runoff.
Determine natural compaction and metamorphosis of snow.
Combine thin snow elements.
Combine two snow elements in terms of temperature, liquid water and
ice contents, and layer thickess.
Divide thick snow elements.
Calculate hydrology for ice and wetland. Maintains a constant water
volume for wetlands and ice.
Determine fate of snow on lake. Force constant lake volume.
Determine age of snow for albedo calculations.
Error checks for energy and water balance.
Accumulate history fields over history time interval.
Route surface and subsurface runoff into rivers for RTM river routing
RTM river routing model.
Main history file handler. This code 1) increments field accumulation
counters at every time step and determines if next time step is
beginning of history interval 2) at the end of a history interval,
increments the current time sample counter, opens a new history file
if needed, writes history data to current history file and resets field
accumulation counters to zero and 3) when a history file is full, or
at the last time step of the simulation, closes history file and
disposes to mass store (only if file is open), resets time sample
counter to zero (only if file is full) and increments file counter by
one (only if file is full)
Write binary restart files.
Write netCDF initial files.