Calibration of in situ eddy dissipation rate (EDR) severity thresholds based on comparisons to turbulence pilot reports (PIREPs)

Turbulence pilot reports, or PIREPs, have long been the standard for reporting turbulent atmospheric conditions to help guide air traffic. PIREPs provide general aircraft position information and a pilot's assessment of the level of turbulence intensity they perceive for a specific airframe. These intensity values are classified into nine severity categories ranging from null to extreme. In order to gather more precise turbulence information, the in situ turbulence algorithm was developed and deployed on aircraft which provides estimates of the atmospheric quantity Eddy Dissipation Rate, or EDR, during every minute of flight and reports these EDR values along with aircraft position information from the aircraft's avionics system. Currently, the in situ EDR algorithm is deployed on 92 United Airlines (UAL) Boeing 757-200 and 73 Delta Air Lines (DAL) Boeing 737-800 aircraft. In this study, PIREP intensity values are compared with EDR measurements reported from the same aircraft. Matches of PIREPs with UAL EDR reports number more than 60,000, and with DAL EDR reports more than 80,000. Comparisons of matched peak (over one minute) EDR vs. PIREP intensity show a monotonic relationship. Fitting a quadratic to the data allows construction of a map between a specific EDR value and a pilot's assessment of turbulence intensity for these aircraft. The fits for the UAL and DAL matches are found to be quite similar. The results imply that the current ICAO standards for EDR levels associated with light, moderate, and severe turbulence thresholds are probably too high.