MOTIONS OF THE SL9 IMPACT CLOUDS

A large number of CCD images of the SL9 impact clouds in the visible f rom July to October 1994 has allowed us to study the morphological cha nges and motions of the impact clouds. Our measurements show the exist ence of at least three different kind of motions: (1) Eastward expansi on during the first two days of the largest impact regions (K, L, G) w ith velocities in the range from 36 to 60 m/s; (2) Clouds that act pro bably as passive tracers of the stratospheric flow (velocities in the range -15 to 20 m/s); (3) Local motions of the cloud elements with mer idional components, sometimes related to the interaction with anticycl onic ovals in nearby latitudes (velocities similar to 20 m/s). The ave rage 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 degrees+/-0.4 degrees.