Gravity waves generated by jets and fronts and their relevance for clear-air turbulence

Jets and fronts are known from observations and modeling studies to be an important source of gravity waves, primarily waves with low intrinsic frequencies. Waves in the jet-exit regions have recurrently been documented and are now rather well understood. Nonetheless, other waves (e.g., involving convection) are also present in the jet/front regions, and there is no simple model available yet to quantitatively predict excited waves from the knowledge of the large-scale flow. Only a handful of case studies have analyzed how jet-generated gravity waves contribute to the occurrence of clear-air turbulence (CAT) in the vicinity of the upper tropospheric jet. They have confirmed that the modulation of vertical shear and stability by strong, low-frequency gravity waves produces localized bands of turbulence. Further studies would be required to discriminate between this and other mechanisms (convectively generated gravity waves, inertial instability) that lead to CAT in the vicinity of jet streaks.