The relationship of satellite-derived cloud motions to actual convective systems within a convectively active phase of the intraseasonal oscillation is examined by using both cloud-scale properties produced by a cloudresolving model and field observations to clarify what is going on at shorter time-and space scales. Each convective system has a life cycle of up to 1-2 days. Described in terms of active convection, the system consists of successive precipitation cells generated ahead of the gust

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... front. Described in terms of its cloud shield, the system is more continuous. When easterly winds prevail above 2 km, both precipitating clouds and uppertropospheric anvil clouds move westward with about the same phase speed (ϳ10 m s Ϫ1 ). However, during the westerly wind period, precipitating clouds move eastward with a phase speed of ϳ10 m s Ϫ1 , which is better represented by the radar observations and surface precipitation. The westward movement of cloud patterns viewed from the satellite images is mostly due to the horizontal advection of the anvil by the mean flow and the creation of new convective cells to the west of the old convective clouds.