Analysing the usage of latent heat in meteorology

Matter in our surroundings exists in three states namely solid, liquid and gaseous. All the three states of matter are interconvertible. The physical state of a substance can change by a change in temperature and pressure conditions. We can change the temperature of a substance by either cooling or heating it. During the change of state of a substance, the heat given to it or released from it is termed latent Heat. Latent Heat can be defined as the energy given/released in the form of heat to change the physical state of a substance.

The meaning of the word Latent is ‘hidden’. The heat energy given during the change of state of a substance does not change the temperature of a substance. There is no change in the temperature of the substance during the phase transformation. To change the state of a substance, the extent of intermolecular forces present in it has to be changed. Solids have the strongest intermolecular forces between the particles, whereas gases have the least forces of attraction between the particles. The energy given in the form of heat is used to overcome the force of attraction between the particles of a particular state of matter which is necessary for the state change. Hence, latent heat does not reflect an increase in temperature. The unit of latent heat is joules. 

• Different types of latent heat are as follows:

• Latent heat of fusion: Fusion is termed as the conversion of a solid-state of a substance to its liquid state. The heat energy required to convert 1 kg of a solid into a liquid substance at its melting point and 1 atm pressure is known as Latent heat of fusion.

• Latent heat of evaporation: Evaporation is termed as the conversion of the liquid state of a substance to its gaseous state. The heat energy required to convert 1 kg of a liquid into the gaseous substance at its boiling point and 1 atm pressure is known as latent heat of evaporation.

• Latent heat of sublimation: Sublimation is the conversion of the solid-state of a substance directly into its gaseous state without converting it into a liquid state. The heat energy required to convert 1 Kg of a solid into a gaseous substance at its melting point and 1 atm pressure is known as latent heat of sublimation.

For a particular substance, latent heat of sublimation is equal to the sum of Latent heat of fusion and evaporation. 

The latent heat of a substance for the processes, such as fusion and sublimation, depends on the values of the temperature and pressure and is different for the different sets of temperature and pressure conditions.

• Specific latent heat: Specific latent heat is the amount of heat energy required to change the state of 1 kg of a substance. Mathematically, 

L = Q/m

Where m is the mass of the substance, Q is the heat energy released/ absorbed in phase transformation and L is the specific latent heat of the substance. Unit of specific latent heat is joules per kilogram (J/kg)

Applications of the latent heat in meteorology

• All the three states of water (ice, water and water vapour) are present at the normal temperature and we can easily see its interconversion daily. Because water is present in large quantities on earth, a large amount of heat is absorbed or released (latent heat) during its change of state. The water cycle in nature depicts the interconversion of three states of water. By the transfer and regulation of latent heat, the water cycle determines atmospheric conditions and circulations. Evaporation is the water cycle that causes cooling, and condensation causes heating. This controls the temperature range of our planet.

• Latent heat is also responsible for various other weather conditions such as cyclones and thunderstorms. When the condensation of water takes place the latent heat is released into the atmosphere and makes the air warmer. Warm air is less dense than cold air and is lighter. Therefore, it moves faster. Fast-moving air causes storms and cyclones. 

Conclusion

A substance can convert from one state to another state through temperature change. Latent heat can be defined as the energy given/released in the form of heat to change the physical state of a substance. The meaning of the word latent is ‘Hidden’. The heat energy given during the change of state of a substance does not change the temperature of a substance. Unit of latent heat is joules.