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MODULE model_mod (Lorenz_04)

Contact: Jeff Anderson
Reviewers:  
Revision: $Revision: 1.4 $
Release Name: $Name: iceland $
Change Date: $Date: 2005/08/05 21:06:51 $
Change history: see CVS log

OVERVIEW

DART interface module for the Lorenz-05 models II and III.  The 13 public interfaces are standardized for all DART compliant models. These interfaces allow DART to advance the model, get the model state and metadata describing this state, find state variables that are close to a given location, and do spatial interpolation for model state variables.

The reference for these models is Lorenz, E.N., 2005: Designing chaotic models.  J. Atmos. Sci., 62, 1574-1587.

Model II is a single-scale model, similar to Loren 96, but with spatial continuity in the waves.  Model III is a two-scale model.  It is fudamentally different from the Lorenz 96 two-scale model because of the spatial continuity and the fact that both scales are projected onto a single variable of integration.  The scale separation is achived by a spatial filter and is therefore not perfect (i.e. there is leakage).  The slow scale in model III is model II, and thus model II is a deficient form of model III.  The basic equations are documented in Lorenz (2005) and also in the model_mod.f90 code.  The user is free to choose model II or III with A NAMElist variable.




OTHER MODULES USED

types_mod
time_manager_mod
oned/location_mod
utilities_mod



PUBLIC INTERFACE

use model_mod, only : get_model_size
 adv_1step
 get_state_meta_data
 model_interpolate
 get_model_time_step
 end_model
 static_init_model
 init_time
 init_conditions
 model_get_close_states
 nc_write_model_atts
 nc_write_model_vars
 nc_read_model_vars
 pert_model_state

NOTES

Optional namelist interface &model_mod_nml may be read from file input.nml.




PUBLIC COMPONENTS




var = get_model_size( )
integer                               :: var

Description

Returns the length of the model state vector as an integer.




call adv_1step(x, time)
real(r8), dimension(:),   intent(inout) :: x
type(time_type),          intent(in)    :: time

Description

Advances a model for a single time step if this operation is defined. The time associated with the initial model state is also required. This interface is only required if `synchronous' model state advance is supported (the model is called directly as a Fortran90 subroutine from the assimilation programs). This is generally not the preferred method for large models which can provide a stub for this interface.

x State vector of length model_size.
time Gives time of the initial model state. Needed for models that have real time state requirements, for instance the computation of radiational parameters. Note that DART provides a time_manager_mod module that is used to support time computations throughout the facility.



call get_state_meta_data(index_in, location, [,var_type] )
integer,                  intent(in)    ::  index_in 
type(location_type),      intent(out)   ::  location 
integer, optional,        intent(out)   ::  var_type 

Description

Returns metadata about a given element, indexed by index_in, in the model state vector. The location defines where the state variable is located (at present, a variety of simple location models for support of gridpoint models are provided) while the type of the variable (for instance temperature, or u wind component) is returned by var_type. The integer values used to indicate different variable types in var_type are themselves defined as public interfaces to model_mod if required. Low order models in which var_type is not necessarily meaningful should simply return a single integer value.

index_in Index into the long state vector.
location Returns location of indexed state variable. The location should use a location_mod that is appropriate for the model domain. For realistic atmospheric models, for instance, a three- dimensional spherical location module that can represent height in a variety of ways is provided.
var_type Returns the type of the indexed state variable as an optional argument.

Notes




call model_interpolate(x, location, itype, obs_val, istatus)
real(r8), dimension(:),   intent(in)  ::  x 
type(location_type),      intent(in)  ::  location 
integer,                  intent(in)  ::  itype 
real(r8),                 intent(out) ::  obs_val 
integer,                  intent(out) ::  istatus 

Description

Given model state, returns the value of variable itype interpolated to a given location by a method of the model's choosing. At present, this is the only support for forward operators that is required from the model_mod. As observations with more complex forward operators are explored a significant additional complexity may be required for forward operator interfaces.

x Model state vector.
location Location to which to interpolate.
itype Integer indexing which type of state variable is to be interpolated. Can be ignored for low order models with a single type of variable.
obs_val The value of the observation from the model.
istatus Quality control information about the observation of the model state. 0 == successful.

Notes




var = get_model_time_step( )
type(time_type)                       :: var

Description

The function name pretty much says it all.

var The base time step of the model. The forecast length.

Notes

In the long run, a more general extended interface may be required that specifies the models range of time stepping possibilities.




call end_model( )

Description

Called when use of a model is completed to clean up storage, etc. Can be a stub for most applications.

Notes




call static_init_model( )

Description

Used for runtime initialization of a model, for instance calculating storage requirements, initializing model parameters, etc. This is the first call made to a model by any DART compliant assimilation routine.

Notes




call init_time(time)
type(time_type),          intent(in)    :: time

Description

Returns the time at which the model will start if no input initial conditions are to be used. This is frequently used to spin-up models from rest, but is often not meaningfully supported in comprehensive GCMs.

time The time at which the model will start if no input initial conditions are to be used.

Notes




call init_conditions( x )
real(r8), dimension(:),   intent(out)   :: x

Description

Returns default initial conditions for model; generally used for spinning up initial model states. For GCMs can conceivably just return 0's if initial state is always to be provided from input files.

x Model state vector.

Notes




call model_get_close_states( o_loc, radius, inum, indices, dist, x)
type(location_type),      intent(in)    :: o_loc
real(r8),                 intent(in)    :: radius
integer,                  intent(out)   :: inum
integer, dimension(:),    intent(out)   :: indices
real(r8), dimension(:),   intent(out)   :: dist
real(r8), dimension(:),   intent(in)    :: x

Description

Returns the number of state variables that are within a given radius (the units for the radius depend upon the location_mod module being used by the model) of an observation at location o_loc. The indices in the long state vector as well as the distance between each close state variable and the observation are also returned, provided there is sufficient storage available for them in the arrays indices and dist. This tends to be the most complicated routine for large models because it must be implemented in a very efficient fashion to support a number of assimilation algorithms.

o_loc Location of observation.
radius Maximum distance between state and observation.
inum Number of close state variables.
indices Indices of close state variables found in long model state vector. If allocated size of this array is too small, only a subset of the close indices is returned. The model_mod gets to decide what subset this is..
dist Distance between observation and state variables indexed in indices array..
x Model state vector. Required by GCMs to calculate vertical distances.

Notes

The Lorenz 04/05 model always does an exhaustive search. (inum = -1)




ierr = nc_write_model_atts(ncFileId)
integer,                              :: ierr
integer,                  intent(in)  :: ncFileId

Description

Function to write model specific attributes to a netCDF file. At present, DART is using the NetCDF format to output diagnostic information. This is not a requirement, and models could choose to provide output in other formats. This function writes the metadata associated with the model to a NetCDF file opened to a file identified by ncFileID.

ncFileId     Integer file descriptor opened to NetCDF file.
ierr Returned error code. 0 == normal termination

Notes




ierr = nc_write_model_vars(ncFileID, statevec, copyindex, timeindex)
integer                               :: ierr
integer,                  intent(in)  :: ncFileID
real(r8), dimension(:),   intent(in)  :: statevec
integer,                  intent(in)  :: copyindex
integer,                  intent(in)  :: timeindex

Description

Writes a copy of the state variables to a NetCDF file. Multiple copies of the state for a given time are supported, allowing, for instance, a single file to include multiple ensemble estimates of the state.

ncFileID     Integer file descriptor connected to NetCDF file.
statevec State vector.
copyindex Integer index to which copy in the file is to be written.
timeindex Integer index of which time in the file is being written.
ierr Returned error code. 0 == normal termination.

Notes




ierr = nc_read_model_vars(ncFileID, statevec, copyindex, timeindex)
integer                               :: ierr
integer,                  intent(in)  :: ncFileID
real(r8), dimension(:),   intent(out) :: statevec
integer,                  intent(in)  :: copyindex
integer,                  intent(in)  :: timeindex

Description

A general interface routine to read the state vector at a particular time for a particular ensemble member.

ierr Returned error code. 0 == normal termination.
ncFileID     Integer file descriptor connected to NetCDF file.
statevec State vector.
copyindex Integer index to designate copy to be read.
timeindex Integer index of desired time to be read.

Notes

This interface is essentially untested in the Lorenz 04/05 model. It began life as a stub, but there is so little to it ... TJH 05 Aug 2005.




call pert_model_state(state, pert_state, interf_provided)
real(r8), dimension(:),   intent(in)    :: state
real(r8), dimension(:),   intent(out)   :: pert_state
logical,                  intent(out)   :: interf_provided

Description

Given a model state, produces a perturbed model state. This is used to generate initial ensemble conditions perturbed around some control trajectory state when one is preparing to spin-up ensembles. A DART compliant model can choose not to provide an implementation of this algorithm and use the default mechanism in DART by simply returning false. as a returned value for the interf_provided argument. In this case, DART perturbs the state to generate ensemble members by adding a random sample from a N(0.0, 0.002) distribution independently to each state variable. Models should override this if some structure is required for perturbations or if the magnitude of perturbations in DART is too large. For instance, the CAM GCM moisture fields have values that are generally much smaller than 0.002 and perturbing them by this magnitude can cause serious model errors.

state State vector to be perturbed.
pert_state Perturbed state vector is returned.
interf_provided Return false to have DART perturb state .

Notes

The Lorenz 04/05 model relies implicitly on the default DART perturbation mechanism, i.e. this routine always returns .false..




NAMELIST

We adhere to the F90 standard of starting A NAMElist with an ampersand '&' and terminating with a slash '/'. If the namelist extends over more than one F90 line, the F90 continuation character must be used, this is also an ampersand (just to confuse things).

namelist / model_nml /  &
   model_size, forcing, delta_t, space_time_scale, coupling, K, smooth_steps, &
    time_step_days, time_step_seconds, model_number

Discussion

This namelist is read in a file called input.nml

Contents Type Description
model_size integer Number of variables in model, default is 960.
forcing real(r8) Forcing, F, for model, default 15.0
delta_t real(r8) Non-dimensional timestep, default 0.001
space_time_scale real(r8) Determines temporal and spatial relationship between fast and slow variables (model III), default 10.0
coupling real(r8) Linear coupling between fast and slow variables (model III), default 3.0
K integer Determines the wavenumber of the slow variables (K=1, smooth_steps=0 reduces model II to Lorenz 96), default 32
smooth_steps integer Determines filter length to separate fast and slow scales, default 16
time_step_days integer Arbitrary real time step days, default 0
time_step_seconds integer Arbitrary real time step seconds (could choose this for proper scaling), default 3600
model_number integer 2 == single-scale, 3 for 2-scale default 3
(This follows the notation in the paper.)



FILES




REFERENCES


ERROR CODES and CONDITIONS

RoutineMessageComment
nc_write_model_atts
nc_write_model_vars
Various NetCDF-f90 interface error messages From one of the NetCDF calls in the named routine



KNOWN BUGS




FUTURE PLANS