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DART interface module for the simple advection 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.
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.
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 num_grid_points = 10, grid_spacing_meters = 100000.0, time_step_days = 0, time_step_seconds = 3600, mean_wind = 20.0, wind_random_amp = 0.00027778, wind_damping_rate = 0.0000027878, lagrangian_for_wind = .true., destruction_rate = 0.000055556, source_random_amp_frac = 0.00001, source_damping_rate = 0.0000027878, source_diurnal_rel_amp = 0.05, source_phase_noise = 0.0, output_state_vector = .false. /
Item | Type | Description |
---|---|---|
num_grid_points | integer | Number of grid points in model. State vector size is 5 times this number. |
grid_spacing_meters | integer | Grid spacing in meters. |
time_step_days | real(r8) | Number of days for dimensional timestep, mapped to delta_t. |
time_step_seconds | real(r8) | Number of seconds for dimensional timestep, mapped to delta_t. |
mean_wind | real(r8) | Base wind velocity (expected value over time) in meters/second. |
wind_random_amp | real(r8) | Random walk amplitude for wind in meters/second^{2}. |
wind_damping_rate | real(r8) | Rate of damping towards mean wind value in fraction/second. |
lagrangian_for_wind | logical | Can use Lagrangian (stable) or Eulerian (unstable) scheme for wind. |
destruction_rate | real(r8) | Tracer destruction rate in fraction/second. |
source_random_amp_frac | real(r8) | Random walk amplitude for source as a fraction of mean source (per second)^{2}. |
source_damping_rate | real(r8) | Damping towards mean source rate in fraction/second. |
source_diurnal_rel_amp | real(r8) | Relative amplitude of diurnal cycle of source (dimensionless). |
source_phase_noise | real(r8) | Amplitude of gaussian noise to be added to source phase offset (per second). |
output_state_vector | logical | Controls the output to netCDF files. If .true., output the raw dart state vector. If .false. output the prognostic version (gridded data) for easier plotting (recommended). |
types_mod time_manager_mod oned/location_mod utilities_mod obs_kind_mod random_seq_mod
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. 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.
model_size | The length of the model state vector. |
real(r8), dimension(:), intent(inout) :: x type(time_type), intent(in) :: time
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 | Specifies time of the initial model state. |
integer, intent(in) :: index_in type(location_type), intent(out) :: location integer, 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 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 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) :: x type(location_type), intent(in) :: location integer, intent(in) :: itype real(r8), intent(out) :: obs_val integer, intent(out) :: istatus
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 | 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 (0 is a good return). This model stops on error, since it should never fail to generate an interpolated value. |
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 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.
A stub since the simple advection model 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 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 | Initial conditions for state vector. |
integer :: nc_write_model_atts integer, intent(in) :: ncFileID
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 to previously-opened netCDF file. |
ierr | Returns a 0 for successful completion. |
integer :: nc_write_model_vars integer, intent(in) :: ncFileID real(r8), dimension(:), intent(in) :: statevec integer, intent(in) :: copyindex integer, 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) :: state real(r8), dimension(:), intent(out) :: pert_state logical, intent(out) :: interf_provided
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 |
type(get_close_type), intent(inout) :: gc real(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) :: gc integer, intent(in) :: num type(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) :: 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(:)
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. |
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
none at this time
N/A
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/simple_advection/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" |