Spatiotemporal characteristics of clear-air turbulence (CAT) potential over East Asia during 1979-2020

Abstract Air turbulence, especially the clear-air turbulence (CAT), always affects flight safety. Based on six CAT diagnostics and ERA5 reanalysis data, the spatiotemporal characteristics of CAT potential in the middle and upper troposphere over East Asia during 1979–2020 and the possible mechanisms are analyzed in this study. The results show that CAT occurs the most frequently in winter and spring at 250–300 and 200–225 hPa, respectively. In general, CAT occurs relatively less in summer and autumn. Besides, the CAT potential decreases with altitude in each season, and the high-magnitude centers gradually move northward and eastward accompanied with a rising motion from winter to summer. During 1979–2020, the CAT potential shows clear increasing trends over most East Asia in winter, while decreasing trends in most regions in summer. In the “high CAT frequency region (HCFR, 75–135°E, 25–45°N) ”, the CAT potential has been significantly increasing in winter and decreasing in summer. Mechanism analysis indicates that the spatiotemporal distribution of East Asian subtropical westerly jet is well correlated with the CAT potential in the HCFR, with the spatial (temporal) correlation coefficients greater than 0.75 (0.54). In addition, the geopotential height pattern in various regions, the zonal circulation in Eurasia and Atlantic, the Polar Vortex, the Subtropical High, and SST all have significant impact on the CAT in the HCFR.