Abstract
Aviation turbulence remains one of the leading causes of weather-related aviation accidents. Therefore, turbulence prediction is a major concern of aviation forecasters. This paper describes the turbulence index (TURBIPMA) developed and used operationally at the Portuguese Institute of Sea and Atmosphere (IPMA), based on several diagnostics derived from ECMWF forecasts, using a new calibration approach. The forecast skill of the TURBIPMA and of individual diagnostics are evaluated using turbulence observations over the Portuguese Flight Information Regions and surrounding areas, for 12 months between February 2020 and March 2021 (excluding May and June). The forecasting skill of the predictors is discussed in terms of the Relative Operating Characteristic (ROC) curves, which is widely applied, but also in terms of novel measures such as the Symmetric Extremal Dependence Index (SEDI) and Symmetric Extreme Dependency Score (SEDS). The new measures are particularly relevant in assessing forecasts of rare events, such as moderate-or-greater turbulence. The operational index outperforms individual diagnostics (such as Ellrod) in terms of all verification measures. Furthermore, the use of a new Richardson number function was proven to be beneficial. Finally, the turbulence prediction by IPMA was comparable to that of the London WAFC for one turbulence episode.
Highlights
Aviation turbulence, experienced as in-flight bumpiness, is atmospheric turbulence caused by turbulent eddies with scales that can affect aircraft in flight
The derived equivalent vertical gust velocity (DEVG) is a turbulence indicator estimated from vertical acceleration, which depends on aircraft mass, equivalent air speed, and empirical constants [18,19]
The performance of several turbulence diagnostics derived from ECMWF forecasts are evaluated over Portuguese flight information regions (FIR) and surrounding areas for the period February 2020 to March 2021, excluding May and June
Summary
Aviation turbulence, experienced as in-flight bumpiness, is atmospheric turbulence caused by turbulent eddies with scales that can affect aircraft in flight. These scales range from about 100 m to 1 km and aircraft bumpiness is most pronounced when the size of the turbulent eddies encountered is about the size of the aircraft [1,2]. For commercial aircraft, this would correspond to eddy dimensions of approximately 100 m [2]. Turbulence remains a major aviation hazard as it is the leading cause of weather-caused accidents worldwide at cruise and descent phases [3]. Turbulence is responsible for tens of millions of losses for the aviation industry per year due to customer injury claims and aircraft damage [2]
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