Clear-air turbulence-aware flight routing over the North Atlantic using weather regimes

Abstract Clear-air turbulence (CAT) is one of the most significant hazards to aviation during the cruise phase. Under climate change, CAT is projected to increase in frequency and severity in certain key areas for aviation, posing growing challenges for flight safety and operational efficiency. This study focuses on the North Atlantic region and investigates how large-scale atmospheric circulation characterised by weather regimes influences the spatial distribution of moderate-or-Greater CAT (MOG-CAT) occurrences. Using ERA5 reanalysis data from 1979 to 2020, we classify daily winter circulation into four weather regimes and compute the MOG-CAT climatology associated with each regime. We then integrate this information into a flight planning model to minimise fuel consumption whilst avoiding areas subject to frequent MOG-CAT. The flights between London Heathrow and New York JFK airports are used as an example. Results show strong regime-dependent variations in MOG-CAT occurrence, reflecting shifts in jet stream position and intensity. For three of the regimes (the negative phase of the North Atlantic Oscillation NAO−, Atlantic ridge and Scandinavian blocking), CAT-aware routing offers turbulence avoidance with minimal fuel and time penalties. In contrast, under NAO+, avoiding MOG-CAT areas can increase round-trip fuel consumption by up to 8%, highlighting a trade-off between safety and efficiency in this high-hazard regime. This regime-based approach has the potential to support CAT hazard assessment and flight route optimisation weeks in advance, thus opening new opportunities for safer and more fuel-efficient flight route planning.