Measurements with the Indian mesosphere-stratosphere-troposphere (MST) radar at Gadanki (13.5 ¿N, 79.2 ¿E) on May 26, 1994, revealed the presence of a Kelvin-Helmholtz instability (KHI) in between two stratified shear layers. The KHI occurred at the shear maximum, at 17.7 km, just above the meteorological tropopause. The characteristic period for the KH wave was found to be 12 min with a billow wavelength of 7.2 km. At the critical level, 17.7 km, the wave showed a sudden change of phase of the order of 160¿. In addition to the characteristic high-signal power bursts, it also exhibited enhanced Doppler width during the occurrence of KHI. This indicates the generation of 3 m scale turbulence in the region where KHI is observed. A detailed investigation of the Doppler width structure reveals that the KH billows undergo breakdown in between the shear layers, causing peaked structure in the Doppler width profile. ¿ 1999 American Geophysical Union