Turbulence and waves in the upper troposphere and lower stratosphere

Abstract

The generation mechanisms and physical characteristics of jet stream turbulence, mountain, and inertia-gravity waves in the upper troposphere and lower stratosphere (UTLS) are investigated for real atmospheric conditions. To resolve multi-scale physical processes of wave breaking and laminated structures in the UTLS region, vertical nesting and adaptive vertical gridding have been developed and applied in nested, high-resolution, coupled mesoscale-microscale simulations. The fully three-dimensional, moist, compressible Navier-Stokes equations are solved with a stretched, adaptive grid in the vertical and improved resolution in the UTLS region. For verification purposes, real-case simulations are conducted for the Terrain-Induced Rotor Experiment (T-REX) campaign of measurements and selected cases from pilot reports (PIREPs). Comparisons with observational datasets highlight significant benefits of nested computational techniques that take into account the shear-stratified turbulence physics of the UTLS. Localized sharp shear layers characterized by stiff gradients of potential temperature and strong alternating vertical velocity patches are resolved in the tropopause region within the embedded microscale nest. We describe fully three-dimensional multiscale dynamics of laminated structures and nonlinear processes in turbulent layers observed in the UTLS region. Depending on atmospheric conditions, the gravity waves might be trapped at the altitude of the jet stream and break or propagate into higher altitudes acquiring characteristics of inertia-gravity waves. Threedimensional instabilities in nonparallel shear-stratified flows such as those induced by mountain and polarized inertia-gravity waves in UTLS are characterized by a polarized Richardson number.