ABSTRACT
On a hot day the picture of clouds building up often signifies that a storm is imminent. We do not always appreciate what is happening, but these growing clouds represent one of the most vital processes in the atmosphere – the condensation of water as it is raised to higher levels and cooled within strong updraughts of air. The water, of course, was derived from the surface – evaporated from the oceans, from the soil, or transpired by the vegetation. But within the atmosphere a variety of events combine to convert the water vapour, which is produced by evaporation, to water droplets. The air must rise and cool for condensation to occur. In this chapter we shall be looking at the nature and consequences of these processes. Precipitation at the ground surface and the evaporation process will be covered in Chapter 5.
