Mountain wave breaking in the lower stratosphere is one of the major causes of atmospheric turbulence encountered in commercial aviation, which in turn is the cause of most weather‐related aircraft incidents. In the case of clear air turbulence (CAT), there are no visual clues and pilots are reliant on operational forecasts and reports from other aircraft. Traditionally mountain waves have been sub‐grid‐scale in global numerical weather prediction (NWP) models, but recent developments in NWP mean that some forecast centres (e.g. the UK Met Office) are now producing operational global forecasts that resolve mountain wave activity explicitly, allowing predictions of mountain wave induced turbulence with greater accuracy and confidence than previously possible. Using a bespoke turbulent kinetic energy diagnostic, the Met Office Unified Model (MetUM) is shown to produce useful forecasts of mountain CAT during three case studies over Greenland, and to outperform the current operational Met Office CAT prediction product (the World Area Forecast Centre (WAFC) London gridded CAT product) in doing so. In a long term, 17‐month, verification, MetUM forecasts yield a turbulence prediction hit rate of 80% with an accompanying false alarm rate of under 40%. These skill scores are a considerable improvement on those reported for the mountain wave component of the WAFC product, although no direct comparison is available. The major implication of this work is that sophisticated global NWP models are now sufficiently advanced to provide skilful forecasts of mountain wave turbulence.
It is well known that encounters with moderate or severe turbulence can lead to passenger and crew injuries and incur high insurance costs for airlines. Atmospheric convection is thought to induce a significant proportion of turbulence experienced by commercial aircraft, but its relative importance over Europe and the northeastern Atlantic Ocean area has not yet been quantified in a systematic way. In this study, a new approach is developed to automatically detect turbulent events associated with convective sources. Observations of convection over Europe and the northeastern Atlantic were obtained from the Met Office Arrival Time Detection system (ATDnet) and from Meteosat Second Generation satellite imagery. The system is run for all in situ reports of turbulence received from a commercial airline for two 6-month periods (summer 2013 and summer 2014). It is found that, as a monthly average, 14% of all aircraft encounters with turbulence occur in the proximity of a convective storm. These findings are interpreted and discussed together with the limitations of the system and observations that were used in this study.
Multiple studies have considered whether increased anthropogenic CO2 will affect the wind speeds and turbulence associated with the winter North Atlantic polar‐front jet stream in the upper atmosphere. Key questions are whether any effects can already be seen and, if so, can they be seen independent of computer models of the atmosphere. In this study we use two reanalyses, NCEP/NCAR and the ECMWF ERA5, and two large observational archives, AMDAR/ACARS and the Global Aircraft Data Set (GADS), to try to answer these questions for the period 2002–2020 when automated aircraft observations were plentiful over the North Atlantic. We focus on eastbound, New York to London, flights. No significant increase appears in reanalyses during the last roughly 40 years (1979–2020) which is our best estimate for the modern satellite era. In contrast, for the last roughly 20 years (2002–2020) both the ERA5 reanalysis (2.5% per year) and the GADS archive (1.2% to 1.4% per year) show a statistically significant rise in the wind speed in the North Atlantic jet streak exit region. These results must be considered in the context of atmospheric oscillations, changes to the North Atlantic Track System (NATS), and the effects of aircraft step climbs. We estimate that up to 0.5% of the rise may be due to improvements in the NATS operations and an unknown additional amount may be due to the substantial increase in automated aircraft observations starting in 1997. We also examine the impact of aircraft observations on one's confidence in drawing conclusions from secular changes in the reanalyses. For turbulence, the Light turbulence trends are not statistically significant. Our confidence in the turbulence results is more limited since these observations reflect medium‐term changes in tactical and strategic aircraft operational procedures as well as the underlying prevalence of turbulence.
<p>Global aviation industry needs are evolving, with increased volumes of traffic, increased capacity demands and the need to limit the environmental impacts of travel. Therefore, the provision of accurate/detailed meteorological information is becoming even more essential for the safe and efficient management of airline and airport operations. &#160;Underpinning much of this is the World Area Forecast System (WAFS), provided by the London and Washington centres, whose capabilities are currently undergoing significant upgrades that promises improved prediction of en-route hazards. These upgrades, focused on atmospheric turbulence, cumulonimbus cloud, and in-flight icing will see the transition of services to a fully probabilistic offering, as well as the provision of a new high-resolution (0.25 degree) deterministic severity-based forecasts of turbulence and icing (replacing the previously used &#8216;potential&#8217; metric). With the delivery of the deterministic products due by 2020, and the probabilistic products due by 2024, we will report on these key developments &#8211; providing both an overview of the new operational diagnostics and their validation, presenting preliminary results from initial trials involving the ensemble data &#8211; enabling users to avoid en-route hazards more safely and efficiently in the future.</p>
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