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1.1.3 Wind Speed Profile

     The wind power law is used to adjust the observed wind speed, uref, from a reference measurement height, zref, to the stack or release height, hs.  The stack height wind speed, us, is used in the Gaussian plume equation (Equation 1-1), and in the plume rise formulas described in Section 1.1.4.  The power law equation is of the form:

where p is the wind profile exponent.  Values of p may be provided by the user as a function of stability category and wind speed class.  Default values are as follows:

 

Stability Category

 

Rural Exponent

 

Urban Exponent

A

0.07

0.15

B

0.07

0.15

C

0.10

0.20

D

0.15

0.25

E

0.35

0.30

F

0.55

0.30

     The stack height wind speed, us, is not allowed to be less than 1.0 m/s.

1.1.4 Plume Rise Formulas

     The plume height is used in the calculation of the Vertical Term described in Section 1.1.6.  The Briggs plume rise equations are discussed below.  The description follows Appendix B of the Addendum to the MPTER User's Guide (Chico and Catalano, 1986) for plumes unaffected by building wakes.  The distance dependent momentum plume rise equations, as described in (Bowers, et al., 1979), are used to determine if the plume is affected by the wake region for building downwash calculations.  These plume rise calculations for wake determination are made assuming no stack‑tip downwash for both the Huber‑Snyder and the Schulman‑Scire methods.  When the model executes the building downwash methods of Schulman and Scire, the reduced plume rise suggestions of Schulman and Scire (1980) are used, as described in Section 1.1.4.11.

 

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