Chapter 3 Solutions — Atmosphere and Climate

The Indian Meteorological Department (IMD) has recognised four distinct seasons in India:

1. Winter (December to early April): The coldest months are December and January. Average temperature in north-west India is 10–15°C, rising to 20–25°C in south-east India.

2. Summer or Pre-monsoon (April to June, or up to July in north-western India): Average temperature across most of inland India ranges from 32–40°C.

3. Monsoon or Rainy — Advancing Monsoon (June to September): Dominated by the humid south-west monsoon, which brings most of India's annual rainfall.

4. Post-monsoon — Retreating Monsoon (October to December): Monsoon retreats from north India in October; south India receives more rainfall during this period.

The atmosphere exerts a significant force on our bodies from all sides — from above, below, and the sides. However, the pressure inside our bodies is equal to the atmospheric pressure and cancels the pressure from outside.

Because air presses on us from all directions equally, and our bodies exert a counter-pressure in response, the forces balance out. As a result, we do not feel the weight or pressure of the atmosphere on us.

Aeroplanes fly in the stratosphere, the second layer of the atmosphere, which extends from the tropopause up to about 50 kilometres.

The stratosphere is ideal for flying aeroplanes for two main reasons: (1) It is completely free of clouds and other weather disturbances such as rainfall, hail, and fog, which are all confined to the troposphere below it. This makes the flight smooth and safe. (2) The stratosphere has stable air conditions, with temperature increasing with altitude, which further reduces turbulence.