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

Usually the top of the inversion is approximately at the height of the top of the valley, so any
plumes emitted into the stable layer aloft will not mix down to the ground until the inversion
breaks down, either through mechanical mixing or convective mixing.
The CALPUFF modeling system will compute inversion breakup fumigation without any user
intervention as long as it is supplied certain key information which includes the following;
� Sufficiently fine enough model resolution (150-250m) so that the nearby terrain
is adequately resolved
� CALMET must be used in order to get a varying spatial distribution of mixing
height across the model domain
� Sufficiently good meteorological data, preferably from a combined approach of
gridded 3-Dimensional data from a prognostic model such as MM5 and
observational data.
Realistic computation of inversion break up fumigation is a function of each of these
interdependent criteria above which are all required in order for the model to have enough
information with respect to the height of the terrain, terrain slopes, temperature profiles, local
flows etc.
3.4.1. Description of how CALMET computes mixing height and its
relevance to properly modeling Inversion-breakup fumigation
In CALMET the daytime mixing height is taken to be the maximum of the convective and
mechanical mixing heights. An upwind looking mixing depth averaging scheme is employed by
the model to avoid an x-y field of mixing heights having unreasonably large cell-to-cell
variations, as each grid cell’s mixing heights are computed independently. In an inversion break
up situation or inland mixing depths during a sea breeze, the upwind looking mixing depth
averaging scheme is able to handle the advective effects of these phenomena. Because CALMET
is explicitly marched in time a simple scheme has been incorporated which approximates the back
trajectory method. For any given grid cell (i,j), the most upwind grid cell would have a direct
impact. An upwind-looking cone originating at (i,j) is then generated to allow smoothing between
cells.
A fine resolution CALMET domain along with good Landuse data and the upwind looking
averaging mixing depth means that the temporal and spatial aspect of inversion breakup can be
captured.
3.5 Buoyant line plumes
CALPUFF contains algorithms to specifically model buoyant line sources
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