AND THE A-TRAIN A New Dimension of Space-Based Observations of Clouds and Precipitation

O ne of the more stunning features of the imagesof earth from space are the clouds that movearound our planet in quasi-organized large-scale systems (e.g., Rossow and Cairns 1995). The character and movement of these coherent cloud fea-tures are primarily governed by the large-scale atmo-spheric circulation and, as such, are an essential mani-festation of weather systems. Motions of synoptic-scale cloud masses, in turn, trace the circulation pat-terns of the atmosphere. By tracking movements of individual cloud elements we can also determine the wind fields (e.g., Menzel 2001). These large cloud systems are not mere passive tracers of wide-scale movement of air. They exert an enormous influence on our weather and climate. Clouds are a fundamental stage of the cycle of water in the atmosphere, condensing water vapor and form