In the SBL the vertical turbulence contains only a mechanical portion which is given by eq. (36).

The use of the same F 2

wm expressions for the SBL and CBL is done to ensure continuity of

turbulence in the limit of neutral stability. Figure 8 illustrates AERMOD’s assumed vertical

turbulence profile for the SBL. This is similar to the profile for the CBL except for a notable

increase in the value of Fwmr. Since values for Fwmr are based on the magnitude of the wind speed

33

Figure 8: Profile of vertical turbulence in the SBL

σ σ σ vT vc vm

2 = 2 + 2 . (38)

at zi, the differences in the two figures stem from setting zo = 0.0001zi in the CBL example case

while for the SBL case zo = 0.001zi.

4.1.6 LATERAL TURBULENCE CALCULATED BY THE INTERFACE

In the CBL the total lateral turbulence, F 2

vT, is computed as a combination of a mechanical

(Fvm) and convective (Fvc) portions such that

In the SBL the total lateral turbulence contains only a mechanical portion. AERMOD, uses the

same Fvm expression in the CBL and SBL. This is done to maintain continuity of Fvm in the limit

of neutral stability. A description of mechanical and convective profiles of lateral turbulence

follows.

4.1.6.1 Mechanical Portion of the Lateral Turbulence

The variation with height of the mechanical portion of the lateral turbulence is bounded by

its value at the surface and an assumed residual value at the top of the mechanical mixed layer.

The variation between these two limits is assumed to be linear. Based on observations from

numerous field studies, Panofsky and Dutton (1984) report that, in purely mechanical turbulence,

the lateral variance near the surface has the form

where the constant, C, ranges between 3 and 5. Based on an analysis of the Kansas data, Izumi

(1971) and Hicks (1985) support the form of eq. (39) with a value of 3.6 for C.

Between the surface and the top of the mechanically mixed layer, F2

vm is assumed to vary

linearly as

 

 

 

n951 - n952 - n953 - n954 - n955 - n956 - n957 - n958 - n959 - n960 - n961 - n962 - n963 - n964 - n965 - n966 - n967 - n968 - n969 - n970 - n971 - n972 - n973 - n974 - n975 - n976 - n977 - n978 - n979 - n980 - n881 - n982 - n983 - n984 - n985 - n986 - n987 - n988 - n989 - n990 - n991 - n992 - n993 - n994 - n995 - n996 - n997 - n998 - n999 - n1000

 

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