ABSTRACT
This chapter examines the next stage of the hydrologic cycle. Clouds consist of tiny ice particles or water droplets, so small and light in weight that impacts from the air's randomly moving molecules are sufficient to keep the particles and droplets from falling. Different kinds of cloud are generated by the cooling caused by uplift, according to the cause of the rising: hills, low-level cold currents, large-scale uplift, convection, or a convergence of winds. Cloud at ground level is fog, if visibility is less than one kilometer; otherwise it is mist. There are various kinds of cloud, and they were originally classified according to shape. Luke Howard was the first to do this, in 1803, recognizing three main groups — streaks, sheets and heaps. Streak clouds were called cirrus (which is Latin for 'hair'), sheet clouds were designated stratus('layer') and a heap cloud is called cumulus('pile'). Layered clouds are called stratiform, whereas billowing clouds are cumuliform.
