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

There are two ways to introduce 3-D prognostic wind data into CALMET when using prognostic
data combined with observations. The first and preferred option is prognostic data as the initial
guess field. In this approach the coarse grid scale prognostic data are interpolated to the
CALMET fine-scale grid. The diagnostic module in CALMET will then adjust the initial guess
field for kinematic effects for terrain, slope flows and terrain blocking effects using fine-scale
CALMET terrain data to produce a Step 1 wind field. Observations are then introduced into the
Step 2 wind field. The second approach is to use prognostic wind data directly as the Step 1 wind
field. This field is then adjusted using observational data, but additional terrain adjustments at the
scale of the CALMET grid resolution are not made. The second approach is not normally
recommended.
All the advantages are the same as for the No-Obs run detailed above, but with additional
complications such as preparing the observational data, optimizing model input to blend the
observations properly with the prognostic data, replacing missing data and making careful site
specific choices with respect to several parameters in the CALMET control file. Relevant useful
references are; Wu et al (1998), Scire and Robe (1977) and Robe and Scire (1998).
2.3.3 Observations Only
This approach ‘Observations only’ relies on standard hourly surface and twice-daily upper air
data and optional hourly precipitation and overwater data to provide the necessary requirements
for the computations of the micrometeorological modules for overwater and overland boundary
layers.
Computation of the wind field in Obs-only mode is a two-step approach in CALMET which uses
the observations twice, once to create the initial guess wind field which is then adjusted for
kinematic effects of terrain, slope flows and terrain blocking effects to produce the Step 1 wind
field. The second step consists of an objective analysis procedure to introduce observational data,
‘more formally’ into the Step 1 wind field to produce a final wind field.
As a minimum CALMET must be provided surface hourly data from one or many stations as well
as radiosonde upper air data at intervals no more than 14 hours apart. Overwater stations and
precipitation data are optional. This modeling approach is advantageous in regions where there is
good representative surface and upper air data near to the facility and the expected area of impact
is nearby, i.e., within a few to several kilometres. However, some complicated choices need to
be made, especially with respect to the radiosonde station which may suffer from missing data
both in-between levels and missing profiles altogether. Further, unless the upper air station is near
to the facility (within 10 – 50km depending on topography) it is not likely to be representative. As
a result the user is left with several critical choices to make which can significantly affect the
final outcome of the model runs.
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