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MODULE model_mod (Lorenz_96)

Contact: Jeff Anderson
Revision: $Revision: 2801 $
Source: $URL: http://subversion.ucar.edu/DAReS/DART/trunk/models/lorenz_96/model_mod.html $
Change Date: $Date: 2007-04-04 22:11:48 -0600 (Wed, 04 Apr 2007) $
Change history: try "svn log" or "svn diff"

OVERVIEW

DART interface module for the Lorenz-96 model. The 17 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.

Quoting from the Lorenz 1998 paper:

... the authors introduce a model consisting of 40 ordinary differential equations, with the dependent variables representing values of some atmospheric quantity at 40 sites spaced equally about a latitude circle. The equations contain quadratic, linear, and constant terms representing advection, dissipation, and external forcing. Numerical integration indicates that small errors (differences between solutions) tend to double in about 2 days. Localized errors tend to spread eastward as they grow, encircling the globe after about 14 days.

...

We have chosen a model with J variables, denoted by X1, ..., XJ; in most of our experiments we have let J = 40. The governing equations are:
dXj/dt = (Xj+1 - Xj-2)Xj-1 - Xj + F         (1)
for j = 1, ..., J. To make Eq. (1) meaningful for all values of j we define X-1 = XJ-1, X0 = XJ, and XJ+1 = X1, so that the variables form a cyclic chain, and may be looked at as values of some unspecified scalar meteorological quantity, perhaps vorticity or temperature, at J equally spaced sites extending around a latitude circle. Nothing will simulate the atmosphere's latitudinal or vertical extent.

See the references section for more details.




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
 nc_write_model_atts
 nc_write_model_vars
 pert_model_state
 get_close_maxdist_init
 get_close_obs_init
 get_close_obs
 ens_mean_for_model

NOTES

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




PUBLIC COMPONENTS

The following routines are public:


var = get_model_size( )
integer                               ::  get_model_size 

Description

Returns the length of the model state vector, which is settable by namelist and defaults to 40.


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. The time associated with the initial model state is also input although is it not used in this model.

x State vector of length model_size
time Gives time of the initial model state


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 For lorenz-96, variable 1 is at 0.0, variable 2 is at 1/40., variable 3 is at 2/40., etc. on a cyclic [0, 1] domain. The variable type is always returned as 1.

index_in Index into the long state vector.
location Returns location of indexed state variable.
var_type If present, always returns 1 as the type

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)                              ::  var 
real(r8),                 intent(out) ::  obs_val 
integer,                  intent(out) ::  istatus 

Description

Given model state, returns the value interpolated to a given location in [0, 1] by linear interpolation. The type variable is not used here and istatus is always returned as 0 (successful interpolation).

x     Model state vector.
location Location to which to interpolate.
itype Not used
obs_val The interpolated value from the model.
istatus Quality control information, always returned 0 (OK)

Notes


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

Description

Returns the models base time step, or forecast length, as a time_type. This is settable via namelist and defaults to 1 hour.

Notes


call end_model( )

Description

A stub since lorenz 96 requires no cleanup.

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(out)    ::  time 

Description

Returns the time at which the model will start if no input initial conditions are to be used. This model sets the time to 0.

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. This model sets all state variables to the forcing value and then perturbs the first variable slightly.

x Model state vector.

Notes


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

Description

Function to write model specific attributes to a netCDF file. 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.

Notes


ierr = nc_write_model_vars(ncFileID, statevec, copyindex, timeindex)
integer                               ::  nc_write_model_vars 
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 opened to NetCDF file.
statevec State vector.
copyindex Integer index to which copy is to be written.
timeindex Integer index of which time in the file is being written.
ierr Returned error code.

Notes


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. Lorenz-96 does not implement an interface for this and returns .false. for interf_provided.

state State vector to be perturbed
pert_state Perturbed state vector is NOT returned
interf_provided Return false to have DART perturb state

Notes


call get_close_maxdist_init(gc, maxdist)
 type(get_close_type), intent(inout) :: gc
 real(r8),             intent(in)    :: maxdist
 

Description

Pass-through to the 1-D locations module. See get_close_maxdist_init() for the documentation of this subroutine.


call get_close_obs_init(gc, num, obs)
 type(get_close_type), intent(inout) :: gc
 integer,              intent(in)    :: num
 type(location_type),  intent(in)    :: obs(num)
 

Description

Pass-through to the 1-D locations module. See get_close_obs_init() for the documentation of this subroutine.


call get_close_obs(gc, base_obs_loc, base_obs_kind, obs, obs_kind, num_close, close_ind [, dist])
 type(get_close_type), intent(in)  :: gc
 type(location_type),  intent(in)  :: base_obs_loc
 integer,              intent(in)  :: base_obs_kind
 type(location_type),  intent(in)  :: obs(:)
 integer,              intent(in)  :: obs_kind(:)
 integer,              intent(out) :: num_close
 integer,              intent(out) :: close_ind(:)
 real(r8), optional,   intent(out) :: dist(:)
 

Description

Pass-through to the 1-D locations module. See get_close_obs() for the documentation of this subroutine.


call ens_mean_for_model(ens_mean)
 real(r8), dimension(:), intent(in)  :: ens_mean
 

Description

A NULL INTERFACE in this model.

ens_mean    Ensemble mean state vector




NAMELIST

We adhere to the F90 standard of starting a namelist with an ampersand '&' and terminating with a slash '/'.

namelist / model_nml /  &
    model_size, forcing, delta_t, time_step_days, time_step_seconds

Discussion

This namelist is read in a file called input.nml

Contents Type Description
model_size integer Number of variables in model, default is 40.
forcing real(r8) Forcing, F, for model, default 8.0
delta_t real(r8) Non-dimensional timestep, default 0.05 This is mapped to the dimensional timestep specified by time_step_days and time_step_seconds.
time_step_days real(r8) Number of days for dimensional timestep, mapped to delta_t. default 0
time_step_seconds real(r8) Number of seconds for dimensional timestep, mapped to delta_t. default 3600



FILES




REFERENCES

Lorenz, E. N., 1995: Predictability: A Problem Partly Solved.  Proc. Seminar on Predictability. 1, ECMWF, Reading, Berkshire, UK, 1-18.

Lorenz, E. N., and K. A. Emanuel, 1998: Optimal sites for supplementary weather observations: Simulations with a small model.  J. Atmos. Sci., 55, 399-414.


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