Cloud observationswere made over the Gulf of Siam, using a passenger flight airplane.Several ring-shaped cloud distributions were observed near the periphery of a convergence zone, and it was considered that they were not look like the usual Benard's cell type motion, but were produced by a several downward air motion near the periphery of the convergence zone.A Cb cloud and a characteristic towering cumulus cloud with cloud bands of starfish-like form were observed.An effective sucking area with about 60 km diameter for the Cb or the towering cloud was estimated from the cloud band distribution.