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DART interface module for the Lorenz-96 model. The 16 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 X_{1}, ..., X_{J}; in most of our experiments we have let J = 40. The governing equations are:

dXfor_{j}/dt = (X_{j+1}- X_{j-2})X_{j-1}- X_{j}+ F (1)j= 1, ..., J. To make Eq. (1) meaningful for all values ofjwe define X_{-1}= X_{J-1}, X_{0}= X_{J}, and X_{J+1}= X_{1}, 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.

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This namelist is read from the file *input.nml*.
Namelists start with an ampersand
'&' and terminate with a slash '/'.
Character strings that contain a '/' must be
enclosed in quotes to prevent them from
prematurely terminating the namelist.

&model_nml model_size = 40, forcing = 8.00, delta_t = 0.05, time_step_days = 0, time_step_seconds = 3600 /

Item | Type | Description |
---|---|---|

model_size | integer | Number of variables in model. |

forcing | real(r8) | Forcing, F, for model. |

delta_t | real(r8) | Non-dimensional timestep. This is mapped to the dimensional timestep specified by time_step_days and time_step_seconds. |

time_step_days | integer | Number of days for dimensional timestep, mapped to delta_t. |

time_step_seconds | integer | Number of seconds for dimensional timestep, mapped to delta_t. |

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types_mod time_manager_mod oned/location_mod utilities_mod

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A note about documentation style.
Optional arguments are enclosed in brackets
*[like this]*.

integer ::get_model_size

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

model_size |
The length of the model state vector. |

real(r8), dimension(:), intent(inout) ::xtype(time_type), intent(in) ::time

Advances the model for a single time step. The time associated with the initial model state is also input although it is not used for the computation.

x |
State vector of length model_size. |

time |
Specifies time of the initial model state. |

integer, intent(in) ::index_intype(location_type), intent(out) ::locationinteger, optional, intent(out) ::var_type

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 of state vector element about which information is requested. |

location |
The location of state variable element. |

var_type |
Returns the type (always 1) of the indexed state variable as an optional argument. |

real(r8), dimension(:), intent(in) ::xtype(location_type), intent(in) ::locationinteger, intent(in) ::itypereal(r8), intent(out) ::obs_valinteger, intent(out) ::istatus

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 |
A 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. |

type(time_type) ::get_model_time_step

Returns the time step (forecast length) of the model; The time step defaults to 1 hour but is settable by namelist.

var |
Smallest time step of model. |

Used for runtime initialization of model; reads namelist, initializes model parameters, etc. This is the first call made to the model by any DART-compliant assimilation routine.

A stub since lorenz 96 requires no cleanup.

type(time_type), intent(out) ::time

Returns the time at which the model will start if no input initial conditions are to be used. This is used to spin-up the model from rest. Sets time to 0 in this model.

time |
Initial model time. |

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

Returns default initial conditions for the model; generally used for spinning up initial model states. Values chosen here are 0.1 for all nine state variables.

x |
Initial conditions for state vector. |

integer ::nc_write_model_attsinteger, intent(in) ::ncFileID

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 to previously-opened netCDF file. |

ierr |
Returns a 0 for successful completion. |

integer ::nc_write_model_varsinteger, intent(in) ::ncFileIDreal(r8), dimension(:), intent(in) ::statevecinteger, intent(in) ::copyindexinteger, intent(in) ::timeindex

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 |
file descriptor to previously-opened netCDF file. |

statevec |
A model state vector. |

copyindex |
Integer index of copy to be written. |

timeindex |
The timestep counter for the given state. |

ierr |
Returns 0 for normal completion. |

real(r8), dimension(:), intent(in) ::statereal(r8), dimension(:), intent(out) ::pert_statelogical, intent(out) ::interf_provided

Given a model state, produces a perturbed model state. This particular model does not implement an interface for this and so returns .false. for interf_provided.

state |
State vector to be perturbed. |

pert_state |
Perturbed state vector: NOT returned. |

interf_provided |
Returned false; interface is not implemented. |

type(get_close_type), intent(inout) ::gcreal(r8), intent(in) ::maxdist

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

type(get_close_type), intent(inout) ::gcinteger, intent(in) ::numtype(location_type), intent(in) ::obs(num)

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

type(get_close_type), intent(in) ::gctype(location_type), intent(in) ::base_obs_locinteger, intent(in) ::base_obs_kindtype(location_type), intent(in) ::obs(:)integer, intent(in) ::obs_kind(:)integer, intent(out) ::num_closeinteger, intent(out) ::close_ind(:)real(r8), optional, intent(out) ::dist(:)

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

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

A NULL INTERFACE in this model.

ens_mean |
State vector containing the ensemble mean. |

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filename | purpose |
---|---|

input.nml | to read the model_mod namelist |

Prior_Diag.nc | the time-history of the model state before assimilation |

Posterior_Diag.nc | the time-history of the model state after assimilation |

dart_log.out [default name] | the run-time diagnostic output |

dart_log.nml [default name] | the record of all the namelists actually USED - contains the default values |

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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.

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Routine | Message | Comment |
---|---|---|

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

none at this time

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none at this time

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N/A

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DART software - Copyright 2004 - 2013 UCAR.

This open source software is provided by UCAR, "as is",

without charge, subject to all terms of use at

http://www.image.ucar.edu/DAReS/DART/DART_download

Contact: | DART core group |

Revision: | $Revision: 6382 $ |

Source: | $URL: https://svn-dares-dart.cgd.ucar.edu/DART/releases/Lanai/models/lorenz_96/model_mod.html $ |

Change Date: | $Date: 2013-08-07 14:45:16 -0600 (Wed, 07 Aug 2013) $ |

Change history: | try "svn log" or "svn diff" |