Generic Guidance and Optimum Model Settings for the CALPUFF ...

2.4 Prognostic-Derived Surface (SURF.DAT) and Upper (UP.DAT) files
In light of the other approaches mentioned above and especially the ease and flexibility of using
3-D gridded prognostic data that is readily available either from MM5, WRF, TAPM or other
simulations, it is not recommended to use the prognostic models to generate single station surface
and upper air meteorological files. In particular in Australasia, TAPM-derived surface and upper
air station files are often used to drive CALMET. These ‘pseudo-profiles’ of surface and upper
air data are used twice in CALMET (once to setup the initial guess phase and a second time in the
Step 2 wind field) and carry the weight of real observations in CALMET. In most instances the
TAPM or other prognostic data is best used as a 3-D input field in CALMET as the initial guess
field rather than as pseudo-stations. The use of the full 3-D field allows all of the spatial
variability in the prognostic model to be carried forward and used by CALMET and using the 3-D
data as the initial guess field allows for smaller-scale terrain adjustments to be made by the
CALMET diagnostic algorithms. Use of pseudo-stations involves the subjective choice of which
“stations” to be selected from the prognostic gridded fields and only partially reproduces the
spatially varying winds of the original prognostic fields.
2.5 Seven Critical CALMET Parameters When Using Observations
When using CALMET with observational data, seven critical parameters must be carefully
assessed and which are unique to every application. These values are; TERRAD, RMAX1,
RMAX2, R1, R2, IEXTRP and BIAS. Table A-1 addresses each of these parameters
individually.
In developing the Step 1 wind field, CALMET adjusts the initial guess field to reflect the effects
of the terrain, including slope flows and blocking effects. At this early stage the model accounts
for the surface and upper air data in the initial guess phase and the user has the choice to use
BIAS parameters to weight the effects of the wind field from an upper air station that may be
located far away and not representative of the facility and site at all. Slope flows are a function of
the local slope and altitude of the nearest crest. The crest is defined as the highest peak within a
radius TERRAD (km) around each grid point. The value of TERRAD is determined based on an
analysis of the characteristic length scale of the surrounding terrain. The Step 1 field produces a
flow field consistent with the fine-scale CALMET terrain resolution.
In Step 2, observations are incorporated into the Step 1 wind field to produce a final wind field.
Each observation site influences the final wind field within a radius of influence (parameters
RMAX1 (km) at the surface and RMAX2 (km) aloft). Observations and the Step 1 wind field are
weighted by means of parameters R1 (km) at the surface and R2 (km) aloft. For example, at a
distance R1 from an observation site, the Step 1 wind field and the surface observations are
weighted equally.
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