5. Condensation and forms of condensation

Generally, when warm air rises, cools down and loses its capacity to hold water vapour, condensation occurs. As a result, excess water vapour present in the air condenses to form cloud droplets.

 

Note: In the previous chapter, we study how, with temperature, water vapour holding capacity of air changes. The capacity increases with an increase in temperature.

 

Condensation is responsible for the formation of clouds. Precipitation occurs when these clouds reach the dew point. Precipitation is the primary route for water to return to the earth's surface in the water cycle. Condensation is the opposite of evaporation.

 

 

\(Dew\ point\ \)is the temperature at which dew forms. It varies widely, depending on location, weather, and time of day.

 

It only occurs in the lower levels of the atmosphere as a sort of dense 'ground cloud'. The visibility in fog is even less than \(1\ \)km. For aviation purposes, the criterion for fog is \(10\ \)km or less.

 

 

The condensation of water vapour in the air causes small droplets of water to float about, forming clouds at a ground level called mist. It reduces visibility to about \(1\ \)km . Mist occurs in wet air when the relative humidity is over \(75\)%. Mist is less dense than fog.

 

 

The white colour of the cloud is due to tiny water droplets tightly packed inside them, reflecting most of the sunlight that hits them. The size of the droplets usually ranges from a few microns to \(100\ \)microns. This is the limit beyond which cloud drops become raindrops.