Observation and backward trajectory of an inertio-gravity wave in the lower stratosphere

A Doppler lidar observation of an inertio-gravity wave in the mid-latitude lower stratosphere is presented. The wave packet characteristics (vertical and horizontal wavenumbers, intrinsic and apparent frequencies) are inferre d from the analysis of the hodograph of the horizontal wind fluctuations. T hose parameters are used as initial conditions for the calculation of the w ave packet trajectory backwards in time in the atmosphere. These calculatio ns are realized by ray-tracing techniques, with background fields (wind and stability) provided by the European Center for Medium-Range Weather Foreca sting analyses. Sensitivity tests are performed in order to estimate the ro bustness of the computed trajectory. It is argued that the generation of th e wave has taken place in the upper troposphere, where evidence of large sy noptic scale Rossby wave disturbances are found. Our results support the fa ct that geostrophic adjustment (and possibly shear instabilities) associate d with such disturbances could be an effective mechanism for the generation of inertia-gravity waves in the mid-latitude.