The 9-variable model is described in Lorenz (1980).1 Lorenz developed this primitive-equation model using shallow-water equations as a starting point and manipulating the divergence equations so that the model exhibits quasi-geostrophic behavior and transient gravity waves that dissipate with time. Gent and McWilliams (1982)2 explore the behavior of this model extensively. For an introduction to shallow-water equations, we recommend consulting the relevant section of a meteorology textbook such as section 4.5 of Holton and Hakim (2013).3
The model's three X variables are at 0, 1/9, and 2/9, three Y variables are at 3/9, 4/9 and 5/9, and three Z variables are at 6/9, 7/9, and 8/9 on a cyclic [0, 1] domain.
In the 9-variable model, DART advances the model, gets the model state and metadata describing this state. The model can be configured by altering the &model_nml
namelist in the input.nml
file. The details of the &model_nml
namelist are always model-specific (there are no generic namelist values). The model time step defaults to 1 hour (3600 seconds) but is settable by altering the namelist.
The 9-variable model has a work/workshop_setup.csh
script that compiles and runs an example. This example is referenced in Sections 7 and 10 of the DART_tutorial <../../../theory/readme>
and is intended to provide insight into model/assimilation behavior. The example may or may not result in good (or even decent!) results!
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
g = 8.0,
deltat = 0.0833333333333333,
time_step_days = 0,
time_step_seconds = 3600
/
Item | Type | Description |
---|---|---|
g | real(r8) | Model parameter, see comp_dt in code for equations. |
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 | 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. |
Lorenz, Edward N., 1980: Attractor Sets and Quasi-Geostrophic Equilibrium. Journal of the Atmospheric Sciences, 37, 1685-1699. doi:10.1175/1520-0469(1980)037<1685:ASAQGE>2.0.CO;2 <https://doi.org/10.1175/1520-0469(1980)037<1685:ASAQGE>2.0.CO;2>__↩
Gent, Peter R., and James C. McWilliams, 1982: Intermediate Model Solutions to the Lorenz Equations: Strange Attractors and Other Phenomena. Journal of the Atmospheric Sciences, 39, 3-13. doi:10.1175/1520-0469(1982)039<0003:IMSTTL>2.0.CO;2 <https://doi.org/10.1175/1520-0469(1982)039<0003:IMSTTL>2.0.CO;2>__↩
Holton, James R., and Gregory J. Hakim, 2013: An Introduction to Dynamic Meteorology -- Fifth Edition. Academic Press, 532 pp.↩