Motions of the SL9 impact clouds

A large number of CCD images of the SL9 impact clouds in the visible from July to October 1994 has allowed us to study the morphological changes and motions of the impact clouds. Our measurements show the existence of at least three different kind of motions: (1) Eastward expansion during the first two days of the largest impact regions (K, L, G) with velocities in the range from 36 to 60 m/s; (2) Clouds that act probably as passive tracers of the stratospheric flow (velocities in the range −15 to 20 m/s); (3) Local motions of the cloud elements with meridional components, sometimes related to the interaction with anticyclonic ovals in nearby latitudes (velocities ∼ 20 m/s). The average zonal velocity relative to System III of the cores of impacts E, A, C, W, K, L, G, R, Q1 and H was (up to 18 August) u = −1.7±1.0 m/s with an average jovicentric latitude of −43.8°±0.4°.