NCERT 7th Class (CBSE) Social Science: Elements of Weather and Climate

Question: How is the Earth’s atmosphere heated? Discuss in detail.

Answer: The heating of the atmosphere takes place in the following ways:

Heating through convection:

1. When air comes in contact with the heated surface of the earth, it gets heated too. Heated air which is lighter than cold air start to rise.
2. Cold air being heavier settles down, taking the place of the rising warm air. The warm air reaching a certain height becomes cold and heavy once more and starts sinking.
3. The transfer of heat through this movement of rising warm air and sinking cold air is called convection and current moving air formed this are called convection currents.

Heating through conduction:

1. Conduction is the transfer of heat from one body to another when they are in direct contact through collisions between the molecules of the two bodies.
2. Conduction is one of the ways that energy is transferred from the earth’s surface to the air. Thus, heat is passed on from the warmer Earth to the cooler air. However, air is poor conductor of heat.

Heating through radiation:

1. Radiation is the energy transmitted from the body to another in the form of rays or waves. The earth absorbs heat from the sun; it then gives off this heat in the form of infrared rays, which are absorbed by the atmosphere and heat it up.

Heating through advection:

1. Advection is the transfer of heat from one region to another.
2. It usually involves the large scale horizontal transfer of energy. For example- Cold polar wind mix with and cool the warmer air of the tropic.
3. When warm winds mix with cooler winds, heat energy is passed on from the warmer wind to the cooler winds through the process of advection.

Question: What is the effect of latitude on temperature?

Answer: The sun rays strike the earth’s surface at different angles from the equator (0°) to the poles (90°). The equatorial region gets the vertical rays of the sun, the polar regions get the slanting rays of the sun. The same amount of sunlight that is focused on, and heats, a smaller area at equator strikes the ground obliquely at the higher latitudes, and is thus spread out over a larger area. So the heating provided by the same amount of sunlight is more in the equatorial regions and much less in the higher latitudes. Hence, the temperature decreases sharply towards the poles.

Question: How does the sea regulate the temperature of the coastal regions? Add a note on ocean currents.

Answer: Places along the coast usually experience moderate climate. This is because:

1. Land gets heated faster than the sea, but it also cools down faster. The oceans take long time to heat up, but once heated, takes longer time to cool down.
2. When the coastal areas are cool down, heat is transferred from the sea to the land, and when the area is heated up, cool air from the sea is transferred to the land.
3. For example- Chennai, which is on the coast, experiences the same climate throughout the year.

Ocean Current: Ocean currents are rivers of hot or cold water that flows within the ocean. Winds that blow over hot ocean currents get heated and carry that heat onto the land they blow over, raising the temperature of the coast there. Similarly, winds that blow onto land after passing over cold currents lower the temperature of that coastal region.

Question: How does the altitude of a place effect its temperature?

Answer: In summer, people go to hill stations to escape heat. This is because temperature decreases with increase in altitude. In the troposphere the temperature decreases at the rate of 1° C for every 160 m ascent (normal lapse rate). This happens because air is densest near the ground and thins rapidly with height. The denser the air, the more is the heat that is trapped. The thinner the air, the more is the heat that escapes. So more the altitude the colder it will be.