Evolution of the SL9 Impact Sites and Numerical Experiments with a Two­Layer Rigid­Lid Model Tadashi Asada Kyushu International University Isao Miyazaki Oriental Astronomical Association Tokuhide Akabane Hida Observatory Ground­based imaging of impact sites of Comet Shoemaker­Levy 9 on Jupiter was carried out in visible and near infrared wavelength. Many impact sites were found to be elongated in east­west direction due to the shear of the zonal #ow. Numerical experiments with two­layer rigid­lid model