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6.4.1 Turner's method

Turner [34] presented a method for determining P-G stability categories from data that are routinely collected at National Weather Service (NWS) stations. The method estimates the effects of net radiation on stability from solar altitude (a function of time of day and time of year), total cloud cover, and ceiling height. Table 6-4 gives the stability class (1=A, 2=B,...) as a function of wind speed and net radiation index. Since the method was developed for use with NWS data, the wind speed is given in knots. The net radiation index is related to the solar altitude (Table 6-5) and is determined from the procedure described in Table 6-6. Solar altitude can be determined from the Smithsonian Meteorological Tables [36]. For EPA regulatory modeling applications, stability categories 6 and 7 (F and G) are combined and considered category 6.

Table 6-4
Turner's Key to the P-G Stability Categories
Wind SpeedNet Radiation Index
(knots)(m/s)43210- 1- 2
0,10 - 0.71123467
2,30.8 - 1.81223467
4,51.9 - 2.81234456
62.9 - 3.32234456
73.4 - 3.82234445
8,93.9 - 4.82334445
104.9 - 5.43344445
115.5 - 5.93344444
12 6.03444444


Table 6-5
Insolation Class as a Function of Solar Altitude
Solar Altitude (degrees)InsolationInsolation Class Number
60 < strong4
35 < 60moderate3
15 < 35slight2
15weak1


Table 6-6
Procedure for Determining the Net Radiation Index
1. If the total cloud1 cover is 10/10 and the ceiling is less that 7,000 feet,  
    use net radiation index equal to 0 (whether day or night)
2. For nighttime: (from one hour before sunset to one hour after sunrise):
a. If total cloud cover 4/10, use net radiation index equal to -2.
b. If total cloud cover > 4/10, use net radiation index equal to -1.
3. For Daytime
a. Determine the insolation class number as a function of solar 
    altitude from Table 6-5
b. If total cloud cover 5/10, use the net radiation index in Table 
    6-4 corresponding to the isolation class number.
  If cloud cover > 5/10, modify the insolation class number using 
    the following six steps.
1.) Ceiling < 7,000 ft, subtract 2
2.) Ceiling 7,000 ft, but < 160,000 ft, subtract 1
3.) Total cloud cover equal to 10/10, subtract 1. (This wil 
     only apply to ceiling 7,000 ft since cases with 10/10 
     coverage below 7,000 ft are considered in item 1 
     above.)
4.) If insolation class number has not been modified by 
     steps 1.), 2.) or 3.) above, assume modified class 
     number equal to insolation class number. 
5.) If modified insolation class number is less than 1, let it 
     equal to 1.
6.) Use the net radiation index in Table 6-4 corresponding to the modified insolation class number.
1 Although Turner indicates total cloud cover, opaque cloud cover is   
    implied by Pasquill and is preferred; EPA
recommended meteorological 
    processors, MPRM and PCRAMMET, will accept either.

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 estimate
  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


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