At least one wind speed measurement, that is representative of the surface layer, is required

for each simulation with AERMOD. Since the logarithmic form does not adequately describe

the profile below the height of obstacles or vegetation, eq.(28) allows for a linear decrease in

wind speed from its value at 7

zo.For the CBL, the R

m’sare evaluated using eq.(7) withzrefreplaced byz, and during stableconditions they are calculated from van Ulden & Holtslag (1985) as

For small

z/L(<<1) and with a series expansion of the exponential term, the first equation in (29)reduces to the form given in eq. (12), i.e., ψ β with $

m =5. However, for largem m= −z L

z/L(>1) and heights as great as 200 m in the SBL, the Rmgiven by eq. (29) is found to fit windobservations much better than the R

mgiven by eq.(12) (van Ulden and Holtslag 1985). Using theexample case parameter values Figure 3 and Figure 4 were constructed to illustrate the form of

the wind profiles used by AERMOD in the layers above and below 7

zo.

4.1.2 WIND DIRECTION PROFILES

For both the CBL & SBL wind direction is assumed to be constant with height both above

the highest and below the lowest measurements. For intermediate heights, AERMOD linearly

interpolates between measurements. At least one wind direction measurement is required for

each AERMOD simulation.

4.1.3 PROFILES OF THE POTENTIAL TEMPERATURE GRADIENT

Above the relatively shallow superadiabatic surface layer, the potential temperature gradient

in the well mixed CBL is taken to be zero. The gradient in the stable interfacial layer just above

the mixed layer is taken from the morning temperature sounding. This gradient is an important

factor in determining the potential for buoyant plume penetration into and above that layer.

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