Describe the role of water vapour in the weather processes.

First : Water vapour absorbs the insolation coming from the sun and thus reduces the amount of insolation reaching the earth’s surface. It also preserves the radiant heat. Thus, it acts as a shield of the earth’s surface. It protects the earth’s surface from the constrasts of very high or very low temperature.

Second : Water vapour causes condensation and precipitation. The water vapour releases and consumes latent heat of the sun through condensation and precipitation processes. The processes of release and consumption cool and warm the air. The condensation process causes the precipitation which falls down on the earth’s surface in various forms.

Third : The amount of water vapour decreases with altitude. Half of the water vapour lies below an altitude of about 2000 metres. It also decreases from the equator towards poles. Its maximum amount lies between 10° and 30° latitudes.

Fourth : Water vapour influences the conditions of stability and instability in the air.