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/ Cont……
Option Parameter Recommended Value Explanation and Justification
Layer dependent weighting factor of
surface vs. upper air wind observations
in defining the Initial Guess Field (IGF)
winds. Observations are always
weighted by inverse distance squared
(1/R 2 BIAS (NZ) Default (NZ * 0) is to not
change the 1/R
) from the station to the grid point.
The BIAS parameter changes that
weight.
2 The BIAS parameter is most often used in complex terrain
situations. The BIAS value ranges from -1 to +1, and a
value is input by the user for each vertical layer. A value of
weighting -1 means the surface station has 100% weight, while a
given equally to surface value of +1 means the upper air station has 100% weight.
and upper air data In simple terrain situation, BIAS is often set to zero (0) for
each vertical layer which means the upper air and surface
Not used in No-Obs mode wind and temperature observations are given equal weight
in the 1/r
Requires user input,
depending on validity of
surface and upper air
stations
2 interpolations used to initialize the
computational domain.
The BIAS affects how the initial Step 1 winds will be
interpolated to each grid cell in each vertical layer based on
upper air and surface observations. By setting BIAS to -1,
we eliminate upper-air observations in the interpolations
for this layer. Conversely by setting BIAS to +1, we
eliminate the surface observations in the interpolations for
this layer.
An example where non-default settings for BIAS may be
used is for a narrow, twisting valley, where the only upperair
observations were 100 km to the west, and the only
local surface wind observations were in one location in the
valley. For this example, we might set BIAS to -1 within
the valley forcing surface data only to be used for the
lowest layers, and BIAS to +1 above the valley forcing
upper air data only to be used aloft, and BIAS might go
from -1 to +1 in the transitional layers at the top of the
valley.
The value of R1 and R2 are used in the construction of the
Weighting parameter for Step 1 wind R1 and R2 No Default
Step 2 wind field, where the observed winds are 'blended'
field vs. observations in Layer 1 (R1)
in with the Step 1 winds and observations. R1 represents
and Layer 2 and above (R2)
the distance from a surface observation station at which the
surface observation and the Step 1 wind field are weighted
equally.
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