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MODULE model_mod (simple_advection)

Contact: Jeff Anderson
Revision: $Revision: 2801 $
Source: $URL: http://subversion.ucar.edu/DAReS/DART/trunk/models/simple_advection/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 simple advection 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.

This model is on a periodic one-dimensional domain. A wind field is modeled using Burger's Equation with an upstream semi-lagrangian differencing. This diffusive numerical scheme is stable and forcing is provided by adding in random gaussian noise to each wind grid variable independently at each timestep. The domain mean value of the wind is relaxed to a constant fixed value set by the namelist parameter mean_wind. The random forcing magnitude is set by namelist parameter wind_random_amp and the damping of the mean wind is controlled by parameter wind_damping_rate. An Eulerian option with centered in space differencing is also provided and can be used by setting namelist parameter lagrangian_for_wind to .false. The Eulerian differencing is both numerically unstable and subject to shock formation. However, it can sometimes be made stable in assimilation mode (see recent work by Majda and collaborators). The model state includes a single passive tracer that is advected by the wind field using semi-lagrangian upstream differencing. The state also includes a tracer source value at each gridpoint. At each time step, the source is added into the concentration at each gridpoint. There is also a constant global destruction of tracer that is controlled by the namelist parameter destruction_rate. The appropriate percentage of tracer is destroyed at each gridpoint at each timestep. The model also includes an associated model for the tracer source rate. At each gridpoint, there is a value of the time mean source rate and a value of the phase offset for a diurnal component of the source rate. The diurnal source rate has an amplitude that is proportional to the source rate (this proportion is controlled by namelist parameter source_diurnal_rel_amp). At each grid point, the source is the sum of the source rate plus the appropriate diurnally varying component. The phase_offset at the gridpoint controls the diurnal phase. The namelist parameter source_phase_noise controls the amplitude of random gaussian noise that is added into the source phase at each time step. If source_phase_noise is zero then the phase offset is fixed. Finally, the time mean source rate is constant in time in the present model version. The time mean source rate controls the amplitude of the diurnal cycle of the tracer source.


OTHER MODULES USED

types_mod
time_manager_mod
oned/location_mod
utilities_mod
obs_kind_mod
random_seq_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. For this model, the length is 5 times the number of grid points. The number of grid points is settable by namelist and defaults to 10, giving a total default size of 50.


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 it is 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 the simple advection model with the default grid size, variable 1 is at 0.0, variable 2 is at 1/10., variable 3 is at 2/10., etc. on a cyclic [0, 1] domain. The variable type, if specified, is an integer kind between 1 and 5. The types are indexed as follows:

index_in Index into the long state vector.
location Returns location of indexed state variable.
var_type If present, returns an index between 1 and 5 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 selects which type (tracer concentration, tracer source, velocity) is being interpolated. istatus is returned as 0 for a successful interpolation.

x     Model state vector.
location Location to which to interpolate.
itype An index variable type
obs_val The interpolated value from the model.
istatus Quality control information (0 is a good return). This model stops on error, since it should never fail to generate an interpolated value.

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 the simple advection model 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.

In this case, it reads the namelist values, allocates space for the state vector, and initializes module variables needed during the run.

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 concentrations to 0, sets up one source, and sets the wind and time/phase defaults to the namelist-specified values.

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. Generates random gaussian values for the tracer concentrations, the U field, the mean source field and the phase.

state State vector to be perturbed
pert_state Perturbed state vector
interf_provided Return .true. because it has code to generate the perturbed 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 /  &
     num_grid_points, grid_spacing_meters, time_step_days, time_step_seconds, &
     mean_wind, wind_random_amp, wind_damping_rate, lagrangian_for_wind, &
     destruction_rate, source_random_amp_frac, source_damping_rate, &
     source_diurnal_rel_amp, source_phase_noise, output_state_vector

Discussion

This namelist is read in a file called input.nml

Contents Type Description
num_grid_points integer Number of grid points in model, default is 10. State vector size is 5 times this number.
grid_spacing_meters integer Grid spacing in meters. Default 100,000 (100 Km)
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
mean_wind real(r8) Base wind velocity (expected value over time) in meters/second. Default 20
wind_random_amp real(r8) Random walk amplitude for wind in meters/second2. Default 1/3600
wind_damping_rate real(r8) Rate of damping towards mean wind value in fraction/second. Default 0.01/3600
lagrangian_for_wind logical Can use Lagrangian (stable) or Eulerian (unstable) scheme for wind. Default .true. (Lagrangian)
destruction_rate real(r8) Tracer destruction rate in fraction/second. Default 0.2/3600
source_random_amp_frac real(r8) Random walk amplitude for source as a fraction of mean source (per second)2. Default 0.00001
source_damping_rate real(r8) Damping towards mean source rate in fraction/second. Default 0.01/3600
source_diurnal_rel_amp real(r8) Relative amplitude of diurnal cycle of source (dimensionless). Default 0.5
source_phase_noise real(r8) Amplitude of gaussian noise to be added to source phase offset (per second). Default 0.0
output_state_vector logical Controls the output to netCDF files. If .true., output the raw dart state vector. Otherwise, output the prognostic version (gridded data) for easier plotting (recommended). Defaults .false. (prognostic format)

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