Historically, explanations of clear-air turbulence (CAT) affecting commercial aviation at cruising altitudes (9-12 km MSL) have invoked shearing instabilities such as Kelvin-Helmholtz instability (KHI). However, in recent decades increasing attention has been given to effects of gravity waves in such turbulence encounters. It is now widely recognized that gravity waves may impact aviation turbulence both directly through wave breaking or, sometimes indirectly, by perturbing environments where the Richardson number is initially small, and thereby allowing KHI or shallow convective instabilities to occur. Furthermore, recent research simulations of observed turbulence cases with numerical weather prediction (NWP) models suggest that aviation turbulence may often be influenced by effects of remotely occurring deep convection or flow interaction with terrain. In this way the physical mechanisms producing CAT in many cases may differ from those thought to produce more classically defined clear-air turbulence. In both convectively-induced and terrain-induced clear-air turbulence, gravity waves often play a crucial role in connecting the mesoscale forcing to the smaller-scale turbulence that the aircraft experience. In this talk we will present examples of convectively-induced turbulence diagnosed using high-resolution NWP simulations of observed turbulence cases in a wide range of different meteorological settings. Particular attention will be focused on the many effects of gravity waves in promoting the turbulence.

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*email: trier@ucar.edu
*Preference: Invited Talk