6.7 Use of Airport Data

Airport data refers to surface weather observations collected in support of various NWS and Federal Aviation Administration (FAA) programs; most, although not all, of the surface weather observation sites are located at airports. For practical purposes, because airport data are readily available, most regulatory modeling was initially performed using these data. However, airport data do not meet this guidance - significant deviations include:

• The instruments used at airports are generally more robust and less sensitive than the instruments recommended in this guidance. For example, the thresholds for measuring wind direction and wind speed are higher than is recommended in this guidance; this results in a greater incidence of calms in airport data.



• Wind direction in airport data bases is reported to the nearest ten degrees - one degree resolution of wind direction is recommended in this guidance.



• Airport data for wind direction and wind speed are 2-minute averages; data for other variables, e.g., temperature and pressure are instantaneous readings - hourly averaging is recommended for all variables in this guidance.

Although data meeting this guidance are preferred, airport data continue to be acceptable for use in modeling. In fact observations of cloud cover and ceiling, data which traditionally have been provided by manual observation, are only available routinely in airport data; both of these variables are needed to calculate stability class using Turner’s method (Section 6.4.1). 

The Guideline on Air Quality Models [1] recommends that modeling applications employing airport data be based on consecutive years of data from the most recent, readily available 5-year period. Airport data are available on the National Climatic Data Center (NCDC) World Wide Web site at http://www.ncdc.noaa.gov/. Documentation and guidance on NWS surface weather observations is provided in the Federal Meteorological Handbook No. 1 “Surface Weather Observations and Reports” [62].

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