null_model
Overview
DART interface module for the ‘null_model’. This model provides very simple models for evaluating filtering algorithms. It can provide simple linear growth around a fixed point, a random draw from a Gaussian, or combinations of the two. Namelist controls can set the width of the Gaussian and change both the model advance method and the expected observation interpolation method.
The 18 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.
Namelist
The &model_nml
namelist is read from the input.nml
file. 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 = 2,
delta_t = 0.05,
time_step_days = 0,
time_step_seconds = 3600
noise_amplitude = 0.0_r8
advance_method = 'simple'
interpolation_method = 'standard'
/
Description of each namelist entry
Item |
Type |
Description |
---|---|---|
model_size |
integer |
Model size. |
delta_t |
real(r8) |
Internal model timestep parameter. |
time_step_days |
integer |
Minimum model advance time in days. |
time_step_seconds |
integer |
Minimum model advance time in seconds. |
noise_amplitude |
real(r8) |
If greater than 0.0 sets the standard deviation of the added Gaussian noise during the model advance. |
advance_method |
character(64) |
Controls the model advance method. The default is ‘simple’ timestepping. A 4-step Runga Kutta method can be selected with the string ‘rk’. |
interpolation_method |
character(64) |
Controls how the expected value of an observation is computed. The default is ‘standard’ which uses a linear interpolation between the two surrounding model points. Other options include ‘square’ which returns the square of the computed value, ‘opposite_side’ which adds on a value from the opposite side of the cyclical domain, and ‘average’ which averages 15 points to get the expected value. Model size should be > 15 to use the last option. |
Files
filename |
purpose |
---|---|
input.nml |
to read the model_mod namelist |
preassim.nc |
the time-history of the model state before assimilation |
analysis.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 |