Measurements with the Aberystwyth VHF radar have revealed a striking illustration of gravity wave generation and breaking in the lowermost stratosphere. Horizontal wind measurements show an inertia-gravity wave that was essentially monochromatic and persisted for longer than 5 days, with a maximum perturbation amplitude of approximately 10 ms-1. Radiosonde measurements show that this wave induced shear instability that led to intense turbulence close to the tropopause. The event was associated with a highly curved jet stream over Europe, suggesting that geostrophic adjustment was a likely source mechanism. ¿ 2001 American Geophysical Union