Water flow in the atmosphere is the essential heat-driven uphill component of the water cycle that lifts water to great altitudes and transports it around the globe. The rest of the cycle is gravity driven and downhill , sustained by continual atmospheric replenishment. Figure 2 is a composite of images from five geosynchronous weather satellites sensing water vapor and clouds in the Earth's atmosphere. Figure 2 A composite satellite image displaying the distribution of water in the middle region of the atmosphere. Bright white patches in the image represent the relatively cold tops of high clouds.
Clouds occur where atmospheric motions are upward.
Medium gray regions depict mainly water vapor. These regions would probably appear clear on visible and ordinary infrared satellite images. Streaks and curls of gray highlight flows of middle atmospheric water vapor transported by large-scale air motions. Dark areas are relatively dry middle atmosphere regions where air is sinking. Midlatitude swirls are storm systems that transport humid warm air poleward to be replaced by colder and drier polar air moving equatorward.