Upward transport of air mass during a generation of orographic waves in the UTLS over the Tibetan Plateau

This work examined the characteristics of an orographic gravity wave event during 0:00 similar to 6:00 UTC on 1 May 2008 and its impacts on stratosphere and troposphere exchange, using NASA MERRA (Modern-Era Retrospective Analysis for Research and Applications) and European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis data and Moderate Resolution Imaging Spectroradiometer ( MODIS) data, in combination with the Weather Research and Forecasting model ( WRF). The results show that the horizontal wavelength is about 600 km throughout the troposphere and stratosphere, close to the terrain width, and the vertical wavelength is about 3 km in the troposphere. The wave structure shows a westward tilt with height. Orographic waves propagate upward into the stratosphere and break up near 150 hPa, leading to a strong attenuation of momentum flux and the release of energy into basic flows. Meanwhile, vertical turbulent mixing is extremely increased and turbulent exchange coefficient enhances more than eight times during a short period (within 1 hour). Large turbulent mixing process causes air transport from the troposphere to the stratosphere, corresponding to the low value of ozone, potential vorticity and buoyancy frequency in the lower stratosphere.