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

Table A-1. An Explanation of the 7 Critical User-Defined, Site Specific Parameters When Using Observational Data in
CALMET
Option Parameter Recommended Value Explanation and Justification
Terrain radius of influence (km)
Vertical extrapolation of surface wind
observations
TERRAD
IEXTRP *1
No Default
Requires user input. Value
in km specific to each
model domain
Used in both No-Obs and
Obs modes
Default is ‘to extrapolate
using similarity theory”
and to exclude upper air
observations from Layer 1
Not used in No-Obs mode
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TERRAD a terrain scale used in computing slope flow
effects (ISLOPE) and terrain blocking effects (IFRADJ) on
the wind field. Consider TERRAD as the distance (km)
that CALMET 'looks' at in computing each of these effects.
For instance the distance of the slope of the nearby terrain
is needed to compute the slope flow. TERRAD should not
be too small otherwise nearby valley walls which
contribute to the slope flow will not be seen. On the other
hand TERRAD must not be so large that hills more than
one valley away is seen. TERRAD can be estimated as the
typical ridge-to-ridge distance divided by two, and usually
rounded up. Typical values of TERRAD are between 5-15
km with an upper limit of about 20 km, however this does
depend on grid resolution (see discussion on terrain
resolution)
This switch affects whether the model allows vertical
extrapolation of surface data or not. This switch was
developed since upper air observations are typically only
taken every 12 hours. The vertical extrapolation of surface
wind observations allows for the hourly surface data to
impact layers above the surface layer.
The default of this value is set to -4, which means
similarity theory is used to extrapolate the surface winds
into the layers aloft, which provides more information on
the observed local effects to the upper layers.
A value of IEXTRP < 0 means that upper-air observations
will not be considered in the Layer 1.