Comparison of In-Situ Turbulence Indicators Obtained from Flight Data

Using aircraft-based observations from an airline in Hong Kong including Airbus aircraft (A320-200, A321-200, A330-300) and Boeing aircraft (B747-400, B777-200, B777-300) from February 2011 to April 2014, Eddy Dissipation Rate (EDR) and Derived Equivalent Vertical Gust velocity (DEVG) as the turbulence indicators are compared. Although flight data used in this study are recorded at every second, the turbulence is counted at every 1-minute intervals using the maximum value of EDR and DEVG during the 1-minute intervals. Because EDR and DEVG are obtained from the same flight data, direct comparisons between these two turbulence indicators are available. Based on ICAO criterion of each level of turbulence against EDR, there are 185053 (84.03 %), 35095 (15.94 %), 79 (0.04 %), and 4 (0.002 %) for null (NIL), light (LGT), moderate (MOD), and severe (SEV) turbulence encounters, respectively. Based on Gills criterion of each level of turbulence against DEVG, there are 212569 (96.52 %), 7425 (3.37 %), 231 (0.1 %), and 6 (0.003%) for NIL, LGT, MOD, and SEV turbulence encounters, respectively. Correlation between EDR and DEVG is larger for Boeing (0.732) than for Airbus (0.416). To examine the ICAO criterion of EDR for each level of turbulence, probability density function and median value of EDR for each bin of DEVG are considered. The EDRs at peak frequency of PDF for LGT, MOD, and SEV level turbulence against the same level of turbulence by Gill's criteria of DEVG are 0.075, 0.225, and 0.475, respectively, for Airbus and 0.075, 0.225, and 0.525, respectively, for Boeing. Using the median values of EDRs for each bin of DEVG, the best-fit curve between EDR and DEVG is determined. Based on the curve, we obtained the low limit of threshold range for LGT, MOD, and SEV turbulence as 0.1185, 0.23325, and 0.4587, respectively, for Airbus and 0.0741, 0.17735, and 0.4514, respectively, for Boeing. These values are somewhat smaller than those by ICAO criteria, as consistent with some previous studies. The results of this study demonstrate that the current ICAO criterion of EDR for each level of aviation turbulence needs to be revised slightly downward and should be different from flight types.