Table of Contents - The Atmospheric Studies Group at TRC

Section 9: CALPUFF
9.16 OPTHILL
When the subgrid scale complex terrain (CTSG) option of the CALPUFF model is invoked, two groups
of additional data must be prepared by the user: CTSG receptor and terrain information. These data may
be provided in external files in the format used by CTDMPLUS (Section 9.12), or they may be entered
into the CALPUFF control file. The purpose of the optimizer program OPTHILL is to provide the user
with the means for calculating the set of terrain data that best characterizes each feature when these data
are entered into the control file.
9.16.1 CTSG Terrain Information
CTSG requires information on the location, orientation, size, and shape of each terrain feature being
modeled. The variables that contain this information are:
xc,yc
thetah
zgrid
relief
expo (1)
expo (2)
scale(1)
scale(2)
axmax(1)
axmax(2)
coordinates (km) of the center of the hill
orientation (deg) of major axis of hill (clockwise from north)
height (m) of "grid-plane" of grid above mean sea level
height (m) of crest of hill above the "grid-plane" elevation
hill-shape exponent for major axis
hill-shape exponent for minor axis
horizontal length scale (m) along major axis
horizontal length scale (m) along minor axis
maximum allowed axis length (m) for major axis
maximum allowed axis length (m) for minor axis
The profile of the terrain along each axis of the feature is prescribed by the following equation:
┌
┐
│ 1 – (x/axmax) expo │
ht(x) = │ ─────────── │ * relief
(9-1)
│ 1 + (x/scale) expo │
└
┘
where ht(x) is the height of the profile above the base of the feature, at a distance x from the peak (Figure
9-1).
The terrain profile-optimizing program (OPTHILL) computes the hill shape exponent (EXPO) and
horizontal terrain length scale (SCALE) parameters from a user-entered terrain profile along each of two
axes. This terrain profile defines the height of the surface of the hill at a number of distances from the
center of the hill, along each axis. The OPTHILL program performs computations for one axis (i.e.,
major or minor axis) of the terrain feature at a time. Therefore, two runs of OPTHILL are necessary for
each subgrid scale terrain feature.
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