Heating and cooling of the atmosphere-Radiation, Conduction, Convection and Advection

Sun is the ultimate source of atmospheric heat and energy, but its effect is not direct.

For example, as we climb a mountain or ascend in the atmosphere, temperature becomes steadily lower, rather than higher.

This is because the mechanism of heating the atmosphere is not simple.

There are four heating processes directly responsible for heating the atmosphere.

They are

[1] Radiation

[2] Conduction

[3] Convection and

[4] Advection


[1] Radiation

Radiation is the process by which solar energy reaches the earth and the earth loses energy to outer space.

When the source of heat transmits heat directly to an object through heat waves, it is known as the radiation process.

In this process, heat travels through the empty space.

The vast amount of heat energy coming to and leaving the earth is in the form of radiation.

Temperature and wavelength are inversely related. Hotter the object shorter is the length of the wave.

Insolation reaches the earth’s surface in short waves and heat is radiated from the earth in long waves.

The atmosphere is transparent to short waves and opaque to long waves.

Hence energy leaving the earth’s surface i.e. terrestrial radiation heats up the atmosphere more than the incoming solar radiation i.e. insolation.


[2] Conduction

When two objects of unequal temperature come in contact with each other, heat energy flow from the warmer object to the cooler object and this process of heat transfer is known as conduction.

The flow continues till the temperature of both the objects becomes equal or the contact is broken.

The conduction in the atmosphere occurs at the zone of contact between the atmosphere and the earth’s surface.

However, this is a minor method of heat transfer in terms of warming the atmosphere since it only affects the air close to the earth’s surface.


[3] Convection

Transfer of heat by movement of a mass or substance from one place to another, generally vertical, is called convection.

The air of the lower layers of the atmosphere gets heated either by the earth’s radiation or by conduction.

The heating of the air leads to its expansion.

Its density decreases and it moves upwards.

The continuous ascent of heated air creates a vacuum in the lower layers of the atmosphere.

As a consequence, cooler air comes down to fill the vacuum, leading to convection.

The cyclic movement associated with the convectional process in the atmosphere transfer heat from the lower layer to the upper layer and heats up the atmosphere.


[4] Advection

Winds carry the temperature of one place to another.

The temperature of a place will rise if it lies on the path of winds coming from warmer regions.

The temperature will fall if the place lies on the path of the winds blowing from cold regions.

This process of horizontal transport of heat by winds is known as advection.

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