where u is the mean measured wind, and the primed quantities refer to the turbulent

fluctuations. The assumption being made is that u u . If we assume that the measured v =

velocity fluctuations correspond only to the angular variations of a constant vector, uv, we can

write from eq. (110) that

In this simple model, uv , is the dilution wind. If we take F

u = F

v, the dilution wind can be written

as

This formulation assures that the dilution wind is not zero as long as either or F

v u is not zero.

Similarly, at the time of plume rise calculations, the effective turbulence and effective wind speed

will be recalculated using eqs. (109) & (112), where the turbulence and winds will be evaluated

at stack top .

7.10 Using Profiles for Interpolating Between Observations

When observations are available AERMOD uses the similarity profile functions to

interpolate adjacent measurements. Figure 18 illustrates how AERMOD’s INTERFACE uses the

expected shape of a meteorological profile to interpolate between observations.

Figure 18: AERMOD’s construction of a continuous meteorological profiles by

interpolating between observations.

For a gridded profile height between two observed profile heights, the observations are

interpolated to the gridded height while maintaining the shape of the similarity profile. This is

accomplished as follows:

1. the observations are linearly interpolated to the gridded profile height;

2. the similarity function is evaluated at the gridded profile height;

3. the similarity function is evaluated at the observed profile heights immediately above

and below the grid height and linearly interpolated to the grid height;

4. the ratio of the value obtained in 2. to the value obtained in 3. is applied to the value

obtained in 1.

For a gridded profile height above the highest observation, the procedure is modified slightly:

1. the observation at the highest observed profile height is extrapolated by persisting the

value upward;

2. the similarity function is evaluated at the grid height;

3. the similarity function is evaluated at the highest height in the observed profile;

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