We study the effect of the Jovian water cloud on internal gravity waves generated by the impact of comet SL9. Vertical structure follows Voyager data to the 1-bar level, a moist adiabat from 1 to 5 bars and a dry adiabat below the 5-bar level. The waves are trapped in the moist layer and propagate horizontally. Their speed is related to the vertical integral of the Brunt-V¿is¿l¿ frequency, and varies as the square root of the water abundance (130 m/s for solar composition). The amplitudes are large, e.g., ¿1 K at a distance of 8000 km for an energy of 1027 ergs. The circular ripples should be detectable one or two days after the impact in thermal infrared and visible images. ¿ American Geophysical Union 1994