Dynamics and Thermodynamics Demonstration Model (DTDM)

Version of May, 2007

The Dynamics and Thermodynamics Demonstration Model is a very simple, two-dimensional compressible numerical model that can be used to illustrate some basic atmospheric sciences concepts and phenomena, including (but not limited to) low- and high-frequency gravity waves produced by heat and momentum sources, sea-breeze circulations generated by differential heating, lifting over cold pools, and Kelvin-Helmholtz instability. The model is written in Fortran 77, driven by input scripts and creates output that can be viewed with the GrADS package. DTDM has been tested on Linux, Mac OS X and other Unix or Unix-like systems, and MS Windows with the g77, g95, IBM (xlf), Portland Group (pgf77) and Intel (ifort) Fortran compilers.

Requirements: Unix-like system/environment (Mac OS X, Linux, Sun Solaris, etc.) or MS Windows, a Fortran 77 or later compiler (g77 and g95 suffice), the GrADS package, and rudimentary command-line skills (using tar, make, a text editor, etc.)

Disclaimer: DTDM is a very simple model which is not guaranteed to be quantitatively accurate and is not presented as a research quality code. May contain bugs and may exaggerate certain physical processes for computational efficiency and/or demonstration purposes. No warranty expressed or implied. Your mileage may vary.

Platform note: On Linux, you may need to alter the scripts to implement byteswapping (byteswap = 1 in the input files). Do a short test case (such as using input_thermal.txt) to see if you need to set the byteswap flag. If you cannot make any plots (all the data are NaNs or similar), you need byteswapping. Alternatively, you can edit the GrADS ctl file and insert "OPTIONS byteswapped" somewhere.

DTDM tutorial slides

DTDM package (revised April, 2007)

For MS Windows: DTDM package zip file Includes executable file dtdm.exe along with source code, input files and example GrADS scripts (350 KB). Specific instructions for Windows version, in PDF format.

DTDM example GrADS output tar file Examples referenced in the tutorial. WARNING: 700 MB compressed tar file; expands to 1 GB.

DTDM2 package (revised May, 2007) <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

DTDM2 is in beta, and contains moisture and friction. Some input scripts have to be modified to include moisture and friction options. See input_sbf_moist.txt as an example of a file that contains such options. At this point, DTDM2 is a "no-cloud cloud model". Supersaturation is rmeoved and condensational heating released, but condensation is not retained. There is no microphysical parameterization.

For Mac OS X, Linux, Unix: DTDM2 package tar file

For MS Windows: DTDM2 package zip file

Examples

(Animations open in new windows.)

Stratospheric gravity waves produced by obstacles

Calm environment

900 sec period	1200 sec period
1800 sec period	2400 sec period

Animation of the 1200 sec period case

Environments with varying stratospheric flows (1200 sec period)

U=0	U=+4 m/s
U=+8 m/s

Obstacle-effect gravity waves above convective roll-like features

U=-3 m/s	U=-6 m/s
U=-9 m/s

Gravity waves excited by heat sources

Steady forcing

1 vertical mode	2 vertical modes

Animations

1 vertical mode, steady forcing
2 vertical modes, steady forcing
2 vertical mode, unsteady forcing (period ~ 21 min)

A simple sea-breeze circulation created by differential surface heating

Effect of cross-shore mean flow

Offshore flow	No mean flow
Onshore flow

Animation of the offshore flow case

Animation with "rolls" excited by random surface heating fluctuations

Effect of the Coriolis force on the sea-breeze circulation

Hovmoller diagrams of surface wind vs. time for three latitudes

60N latitude	30N latitude
Equator

High resolution collapsing cold pool: Kelvin-Helmholtz instability

Potential temperature (shaded)	With vertical velocity
With airflow vectors	With pressure perturbation
With buoyancy pressure	With dynamic pressure

Animation of K-H billow generation and collapse

Lower resolution "storm-adaptive" cold pool

Stable flow over a propagating, maintained cold pool:

Animation of this propagating, maintained cold pool