Invisible Threads: How Jet Stream Shifts areAmplifying Clear Air Turbulence in U.S.Aviation (1980 - 2023)

Abstract

Over the last 10 years, there has been a noticeable increase in Clear Air Turbulence (CAT)incidents reported by commercial airlines, including several recent accidents that have resulted in passenger injuries. This trend is alarming, as CAT poses significant risks to aviation safety and comfort due to its unpredictable nature and lack of visual warning for pilots. One possible explanation for this increase is the impact of changing atmospheric conditions, particularly on the jet stream. Atmospheric reanalysis data were used to analyze jet stream changes over a 43-year period, with a specific focus on deviations from climatological norms in the last decade (2014-2023). Operational Pilot Reports (PIREPs)were implemented to validate the robustness of the turbulence analysis. The study focuses on parameters relevant to commercial aviation and major airline routes over CONUS,including wind speed (|v|), vertical wind shear (VWS), omega (ω), specific humidity (q), temperature (T), ertel potential vorticity (PV), among others. An increase in zonal wind speeds within the jet stream was found, contributing to a poleward shift during winter and fall months in recent years. Additionally, increases in vertical wind shear at critical flight levels correspond to regions where CAT is more likely to occur. Moreover,rising mean |ω| throughout the year indicate more pronounced regions of upward and downward air movement that may interact with the jet stream to produce CAT. Regional hot spots were identified over the Northeast and Midwest, emphasizing areas of increased aviation risk in recent years. These findings suggest that conditions conducive to CAT are becoming more prevalent, particularly along major airline routes. Thus, CAT can lead to increased fuel consumption and delays as pilots are forced to circumvent affected areas,further impacting the efficiency of flight operations. In general, this study emphasizes the importance of integrating reanalysis and observational data to understand turbulence-relevant parameters from the perspective of changing atmospheric conditions at upper levels.