Objective Verification of Clear-Air Turbulence (CAT) Diagnostic Performance in China Using In-Situ Aircraft Observation

Abstract This study analyzes the spatial and temporal distribution characteristics of the in-situ aircraft observations in the middle and higher troposphere in 2019. These aircraft observations are mainly distributed in China, and relatively evenly recorded between 00-15 UTC in time and 6-10 km in height. Based on the 3,395 stronger clear-air turbulence (CAT) events and 4,038 weaker CAT events selected from the observations in the study region (15-55 °N, 70-140 °E), the performances of 24 CAT diagnostics calculated from the ERA5 reanalysis data are evaluated. Results show that the diagnostics connected with vertical wind shear (i.e. version 1 of the North Carolina State University index, negative Richardson number, variant 3 and variant 1 of Ellrod’s turbulence index) have the best performances. However, the performances vary greatly from season to season that best in winter and worst in summer. The annual and seasonal best thresholds for these diagnostics are also listed in this study.