Multi-scale simulations of three dimensional laminated structures induced by mountain waves in the UTLS region during T-REX

High-resolution mesoscale and microscale simulations of wave breaking and laminated structures induced by mountain waves in the upper troposphere and lower stratosphere (UTLS) are presented for two Intensive Observational Periods (IOPs) of the Terrain-induced Rotor Experiment (T-REX). To resolve multi-scale nonlinear processes in the UTLS, vertical nesting and refined vertical gridding have been developed and applied within a microscale model that was coupled to the mesoscale Weather Research and Forecasting (WRF) model. In these simulations, the finest nest of WRF is coupled with embedded microscale nests, within which the fully three-dimensional, nonhydrostatic, compressible Navier-Stokes equations are solved with a stretched, refined grid in the vertical and improved resolution in the UTLS region. For nesting, both lateral and vertical boundary conditions are treated via relaxation zones where the velocity and temperature fields are relaxed to those obtained from the mesoscale WRF inner nest. Realcase simulations of two T-REX IOPs are based on initial and boundary conditions from high resolution T799 L91 ECMWF analysis data. Within the embedded microscale nests, localized sharp shear layers and stiff gradients of vertical velocity and potential temperature are predicted above the tropopause and in the lower stratosphere. Potential temperature and velocity fields resulting from fully resolved three-dimensional instability mechanisms and multi-scale dynamics in UTLS show favorable agreement with in situ balloon and aircraft observations obtained during T-REX.