Since algorithms used for profiling differ in the SBL and CBL, the stability of the PBL must

be determined. For this purpose the sign of L is used by AERMET; if L < 0 then the PBL is

considered to be convective (CBL) otherwise it is stable (SBL).

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4 Vertical Structure of the PBL - AERMOD’s Meteorological Interface

The AERMOD interface, a set of routines within AERMOD, uses similarity relationships

with the boundary layer parameters, the measured meteorological data, and other site-specific

information provided by AERMET to compute vertical profiles of: 1) wind direction, 2) wind

speed, 3) temperature, 4) vertical potential temperature gradient, 5) vertical turbulence (Fw ) and

6) lateral turbulence ( F

v ).

For any one of these six variables (or parameters), the interface (in constructing the profile)

compares each height at which a meteorological variable must be calculated with the heights at

which observations were made and if it is below the lowest measurement or above the highest

measurement (or in some cases data is available at only one height), the interface computes an

appropriate value from selected PBL similarity profiling relationships. If data are available both

above and below a given height, an interpolation is performed which is based on both the

measured data and the shape of the computed profile (see Section 7.10). Thus the approach used

for profiling, simultaneously takes advantage of the information contained in both the

measurements and similarity parameterizations. As will be discussed, at least one level of

measured wind speed, wind direction, and temperature is required. However, turbulence profiles

can be parameterized without any direct turbulence measurements.

The following sections provide a comprehensive description of AERMOD’s profiling

equations and how these estimated profiles are used to extract pertinent layer-averaged

meteorology for AERMOD’s transport and dispersion calculations. Also, example profiles (one

typical of the CBL and one typical of the SBL) for the various parameters have been constructed

for illustration. The CBL case assumes that zi = 1000 m, L = -10 m and zo = 0.1 m (i.e., zo =

0.0001zi and L = - 0.01zi). The SBL case assumes that zi = 100 m, L = 10 m and zo = 0.1 m (i.e.,

zo = 0.001 zi and L = 0.1 zi).

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