6.6.1 The Profile Method

The bulk Richardson number given in (6.6.3) is perhaps the simplest and most direct approach for characterizing the surface layer. For example, given the necessary surface layer measurements, one can derive both H and u* from the integrated flux-profile equations: [51,52] 

 

where R is a parameter associated with the empirically determined similarity functions, _m and _h . The U.S. EPA recommends using the empirical functions given in reference [59]; in this case the von Karman constant, k = 0.4 and R = 1. The temperature scale  _* is related to the heat flux by:

Methods for solving the flux profile equations vary depending on what measurements are available. In the general case with two arbitrary levels each of temperature and wind speed [i.e., as in (6.6.4) and (6.6.5) ], one can solve for the unknowns (u_* ,  _* , and L) by iteration; when temperature and wind speed are measured at the same heights, approximate analytic solutions can be used. 

Other simplifications result by replacing the lower wind speed measurement height in (6.6.4), z_i , with the surface roughness length (z₀ ) [51,52] ; see Section 6.6.3 for guidance on estimating surface roughness. A least squares method [49] is recommended when wind speed and temperature data are available for three or more levels. To ensure the data are representative of the surface layer, the wind speed and temperature sensors should be located between 20z₀ and 100z₀ ; for sites with very low roughness, the sensors should be located between 1 and 10 m. Sampling durations for use in computing 1-hour averages should be in the range of 3 to 60 minutes; a sampling duration of 15 minutes or less is recommended if the steady-state assumption is in doubt.

6. METEOROLOGICAL DATA PROCESSING
  6.1 Averaging and Sampling Strategies 
  6.2 Wind Direction and Wind Speed 
      6.2.1 Scalar Computations 
      6.2.2 Vector Computations 
      6.2.3 Treatment of Calms  
      6.2.4 Turbulence 
      6.2.5 Wind Speed Profiles  
  6.3 Temperature 
      6.3.1 Use in Plume-Rise Estimates  
      6.3.2 Vertical Temperature Gradient 
  6.4 Stability 
      6.4.1 Turner's method  
      6.4.2 Solar radiation/delta-T (SRDT) method 
      6.4.3  _E method 
      6.4.4 _Amethod 
      6.4.5 Accuracy of stability category estimates 
  6.5 Mixing Height 
      6.5.1 The Holzworth Method  
  6.6 Boundary Layer Parameters  
      6.6.1 The Profile Method 
      6.6.2 The Energy Budget Method  
      6.6.3 Surface Roughness Length 
      6.6.4 Guidance for Measurements in the Surface Layer 
  6.7 Use of Airport Data 
  6.8 Treatment of Missing Data  
      6.8.1 Substitution Procedures 
  6.9 Recommendations