Heating and Cooling of Atmosphere

The atmosphere experiences heating and cooling through various mechanisms:

1. Conduction: When the Earth’s surface is heated by incoming solar radiation, it transfers heat to the adjacent atmospheric layers in the form of long-wave radiation. This gradual heating of the air in contact with the land is termed conduction. Conduction occurs when two bodies at different temperatures come into contact, causing energy to flow from the warmer body to the cooler one. This process is crucial for heating the lower atmospheric layers.
2. Convection: As the air near the Earth’s surface is heated, it rises vertically in the form of currents, transmitting heat throughout the atmosphere. This vertical heating process is known as convection and is confined to the troposphere.
3. Advection: Heat transfer through horizontal movement of air is referred to as advection. Horizontal air movement plays a significant role in influencing daily weather patterns, particularly in middle latitudes. For example, advection contributes to the occurrence of local winds like the ‘loo’ in northern India during the summer season.

Terrestrial Radiation

After receiving insolation from the Sun, the Earth’s surface emits heat energy in the form of long-wave radiation. Roughly 35 units of incoming solar radiation are reflected back to space, with the remaining 65 units absorbed by the Earth’s surface. The Earth then radiates back 51 units of heat energy, with 34 units absorbed by the atmosphere and 17 units radiated directly to space.

Heat Budget of the Earth

The Earth’s heat budget, illustrated in Figure 9.2, demonstrates a balance between incoming solar radiation and outgoing terrestrial radiation. This balance ensures that the Earth’s temperature remains relatively constant. The atmosphere indirectly receives heat from the Earth’s surface through terrestrial radiation, and this energy is eventually radiated back into space, maintaining thermal equilibrium.

Variation in Net Heat Budget at Earth’s Surface

There are variations in the amount of radiation received at different latitudes, resulting in regional differences in the net radiation balance. Figure 8.3 illustrates that regions between 40 degrees north and south experience a surplus of net radiation balance, while polar regions have a deficit. The surplus heat from the tropics is redistributed towards the poles, preventing excessive heating in the tropics or permanent freezing in high latitudes due to accumulated heat deficit.

Class 11 Notes Chapter 8 discusses Solar Radiation, Heat Balance, and Temperature. Solar radiation is an electromagnetic energy that is released by the sun. It is the major and primary source of the land heating process and also helps in the photosynthesis process. Heat balance is a natural phenomenon that helps the atmosphere absorb a certain amount of heat from the sun and release that same amount of heat into space. To sum up, we can say the temperature of our planet is neither too hot nor too cold as it always supports the life present on it.

In this article, we are going to discuss Chapter 8 by considering Solar Radiation, Heat Balance, and Temperature in detail.