Numerical simulations and observations of large-amplitude inertia-gravity wave breaking over the western lee of Greenland associated with commercial aviation encounters with severe clear-air turbulence

Historical records of aviation turbulence encounters in the vicinity of Greenland for the period from 2000 to 2006 were used to identify an important flow regime that contribute to the occurrence of aircraft turbulence associated with the passage of synoptic-scale cyclones that direct easterly or southeasterly flow over Greenland's imposing terrain. An effect of this easterly lower-tropospheric incident flow is the generation of mountain waves that may become unstable through interactions with the background directional wind shear. It is shown that this regime accounts for approximately 40 percent of the significant turbulent events identified in the seven-year database. Select cases are examined in more detail through high-resolution regional numerical simulations. Results highlight the role of three-dimensional gravity waves,their critical-level interactions and the utility of high-resolution forecasts in the prediction of such events. A recent event from 25 May 2010 resulted in multiple passenger injuries requiring the London-to- Los Angeles flight to be diverted to Montreal, Canada. The numerical simulation for this incident clearly identifies large-amplitude gravity-wave breaking over the western lee of Greenland, which maximized near the tropopause and coincident with the time and altitude of the aircraft turbulence encounter.