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 7zo.
For the CBL, theRm’s are evaluated using eq.(7) with zref replaced by z, and during stable
conditions they are calculated from van Ulden & Holtslag (1985) as
For smallz/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 large m m= − z L
z/L(>1) and heights as great as 200 m in the SBL, the Rm given by eq. (29) is found to fit wind
observations much better than theRm given by eq.(12) (van Ulden and Holtslag 1985). Using the
example 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 7zo.
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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