AirWare
air quality assessment & management
Reference and User Manual
AirWare   On-line Reference Manual
  Release Level 7.0
  Revision Level beta
  Release Date 2015 03

DWM: A Diagnostic Multi-layer Wind Model

One of the most important elements of any atmospheric simulation system is the computation of a realistic wind field in a complex terrain. The Diagnostic Wind Model (DWM, Douglas 1990) generates quasi steady-state gridded wind fields for each set of input conditions. It adjusts the domain-scale mean wind for terrain effects (kinematic effects like lifting and acceleration of the airflow over terrain obstacles as well as thermodynamically generated slope flows). It performs a divergence minimization to ensure mass conservation.

The model can use one or more meteorological stations the user can select in the meteorological scenario object interface.

Vertical and horizontal structure

DWM uses a number of vertical layers; these are consistent with the vertical structure in CAMx and its meteo scenario.

If MM5 is used as a meteorological pre-processor, these layer definitions are used to generated the required vertical structure by the MM5 post-processor that generates the CAMx input files.

The horizontal resolution of the computational grid is set to 1,000 m.

  Vertical layers (in meters)
0   -   25
25 - 50
50 - 100
100 - 200
200 - 500
500 - 1000
1000 - 2000
2000 - 4000

The following steps are performed in the DWM calculations:

  • STEP 0: selection of the appropriate parametrization for the given meteorological conditions.
  • STEP 1: construction of an inert vertical wind profile depending on atmospheric stability and determination of a set of stability parameters (Ermak 1991).
  • STEP 2: parametrization of kinematic terrain effects (Liu 1980).
  • STEP 3: intermediate divergence minimization to adjust the horizontal wind components in each vertical level (Goodin 1980).
  • STEP 4: computation of thermodynamically generated slope flows, modifies the horizontal surface wind components (Allwine 1985).
  • STEP 5: Froude number adjustment for the horizontal wind (Allwine 1985).
  • STEP 6: smoothing of the horizontal wind field.
  • STEP 7: divergence computation of the horizontal field, new vertical wind components.
  • STEP 8: vertical adjustment of the vertical wind (zero at the top or at the mixing h eight) (O'Brien 1970).
  • STEP 9: final divergence minimization to adjust the horizontal wind -> final wind field.
The model output is a terrain and atmospheric stability-adjusted 3D wind field with its appropriate stability parameters.

References

Allwine K.J., Whiteman C.D. (1985)
MELSAR: A Mesoscale Air Quality Model for Complex Terrain: Volume 1 - Overview, Technical Description and Users Guide. Pacific Northwest Laboratory, Richland (PNL-5460).
Ermak L.D. (1991)
User's Manual for SLAB: An Atmospheric Dispersion Model for Denser-Than-Air Releases. National Technical Information Services (NTIS), DE91- 008443, Springfield, VA.
Douglas G.S., Kessler R.C., Carr L. (1990)
User's Manual for the Diagnostic Wind Model. EPA-450/4-90-007C.
O'Brien J.J. (1970)
Alternative solutions to the classical vertical velocity profile. J. Applied Meteorol., 9: 197-203.


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