Clear Air Turbulence Resolved by Numerical Weather Prediction Model Validated by Onboard and Virtual Flight Data

A clear air turbulence (CAT) occurred on 30 December 2020 over Tokyo, Japan. The CAT was largely generated by breaking Kelvin‐Helmholtz (KH) instability waves in the free atmosphere. A regional numerical weather prediction model simulated the event with fine resolution (35 m). Onboard‐recorded flight data and a flight simulation were utilized to validate the meteorological simulation. The locations of the reproduced strong turbulence agree well with the regions where flights encountered turbulence on that day. In a simulation with the finest resolution, the KH waves and their breaking were resolved. When the resolution was finer, the turbulent eddies were stronger, causing meteorological effects on the airplanes. The response of a virtual airplane to the simulated turbulence was estimated using a flight simulation. By comparing onboard‐recorded data with virtual flight data, we confirm that turbulent eddies are reasonably reproduced. Plain Language Summary Clear air turbulence (CAT) is a threat to aviation safety. CAT occurs outside clouds, making it difficult to detect by pilots and onboard radars. When an airplane encounters strong CAT, changes in aerodynamic forces and moments cause significant shaking of the airplane. Although CAT generation in the free atmosphere has been studied by high‐resolution numerical simulations, few studies simulated aircraft‐scale turbulence eddies and validated them with high‐frequency airborne observation. We investigate a past CAT event in Japan using a very high resolution (35 m) simulation based on a regional weather prediction model of daily weather forecasts. The simulated turbulence was verified by comparing the virtual flight in simulated wind fields with realistic flight data recorded by airplanes during the event. Simulated aircraft responses in finer weather simulations match flight records better. Key Points Clear air turbulence in a real case is reproduced by the use of a numerical weather prediction model If the resolution is fine enough for a large eddy simulation (LES), turbulent eddies associated with Kelvin‐Helmholtz instability are reproduced Turbulence eddies are shown to be realistic because virtual flight data in the LES data agree well with real flights