AirWare On-line Reference Manual
| Release Level | 5.3.0 beta |
| Release Date | 2007 06 |
Revision Level | 1.1 |
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.
