Explain the basic mechanisms of heat transfer. 

There are four basic mechanisms of heat transfer. They are explained below:

i. Conduction: In this, the heat flows from the hotter zone to the colder zone through matter by molecular activity. When two bodies of unequal temperature are in contact with one another, the molecules of warmer body transfer heat to the molecules of colder body. This process of transfer of heat continues until both bodies attain the same temperature or the contact is broken. This mechanism of transfer of heat is important only in the Lower layers of the atmosphere because the ability of the substances to conduct heat varies.

ii. Convection: In this mechanism, the heat is transferred from hotter zone to the colder zone by the movement of a mass or substance. Convective motions are possible only in liquids and gases.

When the air of lower layers of the atmosphere gets heated by terrestrial radiation or conduction, it expands. Owing to decrease in density, it moves upwards. It pushes the air to higher level which moves upward. The vacuum created by the wind causes horizontal movement in the air. Thus, the wind moving horizontally on the earth's surface reaches the heated region from where it again ascends. In this way, the heat is transferred from the lower layers to the upper layers of the atmosphere. This mechanism of heating is known as Convection.

(3) Radiation: Radiation means the transfer of heat through a medium without affecting it. So the atmosphere does not get heat from the rays of the sun but it is heated by the terrestrial radiation.

(4) Advection: In this mechanisms, there is horizontal movement of the air masses. Thus these air masses transfer heat from equatorial regions to the polar regions.

Out of these mechanisms of heat transfer, conduction is the least important meteorologically because air is fluid and is a poor conductor of heat. It has its value in the lower layers of the atmosphere where the air is in direct contact with the earth's surface.