Observations and Numerical Simulations of Inertia–Gravity Waves and Shearing Instabilities in the Vicinity of a Jet Stream

The characteristics and dynamics of inertia-gravity waves generated in the vicinity of an intense jet stream/upper-level frontal system on 18 February 2001 are investigated using observations from the NOAA Gulfstream-IV research aircraft and numerical simulations. Aircraft dropsonde observations and numerical simulations elucidate the detailed mesoscale structure of this system, including its associated inertia-gravity waves and clear-air turbulence. Results from a multiply nested numerical model show inertia-gravity wave development above the developing jet/front system. These inertia-gravity waves propagate through the highly sheared flow above the jet stream, perturb the background wind shear and stability, and create bands of reduced and increased Richardson numbers. These bands of reduced Richardson numbers are regions of likely Kelvin-Helmholtz instability and a possible source of the clear-air turbulence that was observed.