Long Question Answers : Composition and Structure of Atmosphere | Geography Class 11 - Humanities/Arts PDF Download

Q. 1. Describe the role of water vapour in the weather processes.
Ans. Water Vapour: Water vapour is the result of evaporation from water bodies on the earth. Water vapour represents about 2 percent of the air by volume.
The presence of water vapour in the atmosphere is of primary importance in weather phenomena.
(i) It reduces the amount of insolation reaching the earth’s surface by absorption.
(ii) It acts like an insulating blanket by preserving the earth radiation. It allows the earth neither to become too cold nor too hot.
(iii) Water vapour is the basic cause of all condensation and precipitation.
(iv) Water vapour condenses into clouds and fog.
(v) Water vapour is the main source of energy giving rise to cyclones, storms, etc.
(vi) Water vapour both releases and consumes latent heat of condensation which cools and warms the air.
(vii) Water vapour makes the air stable and unstable.

Q. 2. Why is the height of troposphere the greatest at the equator ?
Ans. The height of the troposphere varies from one place to another. It is 8 kms. at the poles and 20 kms. at the equator. The equator receives the maximum amount of insolation. The heated surface gives rise to strong convection currents. These currents transport the heat to great heights. The light air rises and increases the zone of troposphere. In other areas, due to low temperatures, descending winds reduce the height of the troposphere.

Q. 3. Explain the Importance of the Atmosphere.
Ans. The atmosphere  is useful for man in the following fields : 

1. Basis of Life: Atmosphere is the very basis of life on the earth. We cannot even imagine life without atmosphere. Atmosphere contains oxygen which is very essential for human existence and carbon dioxide is useful for vegetation. The earth is the only planet having atmosphere.
2. Weather: Weather has a great influence on our life. Evaporation, precipitation, winds, etc., take place due to atmosphere.
3. Heat Balance: Atmosphere acts as a greenhouse for us. The ‘Green House’ effect keeps Earth’s temperature at an average of 35°C. Without atmosphere, under extremes of temperature life would have been impossible.
4. Harmful Radiations: A layer of ozone gas absorbs the ultraviolet radiations coming from the sun. The ozone, layer, thus protects the earth from ultraviolet radiation.
5. Radio Broadcasting: Ionosphere layer of the atmosphere reflects the radio waves transmitted from the earth and sends them back to earth. This helps in radio-broadcasting.
6. Safeguard against Meteorites: Meteorites are constantly falling from outer space towards the earth. Most of these are burnt in atmosphere.
7. Aviation: Aeroplanes fly in this medium of atmosphere. Jet planes fly in stratosphere (upper layers).

Q. 4. Explain, with examples, the difference between weather and climate.
Ans. The term ‘weather’ should not be confused with ‘climate’ though they are very closely related to each other in the study of meteorology and climatology.

Weather: Weather is the sum total of atmospheric conditions at any place at any specific time. The weather changes from day-to-day, and hour-to-hour.
We often speak of hot ‘weather’, ‘windy’ weather, a cold morning, ‘a sunny afternoon’ etc. Weather stands for the atmospheric conditions for a short period : for a day, a week or a month. That is the reason why the All India Radio broadcasts the weather conditions. The Indian Meteorological Department publishes the daily Indian Weather Maps. In Britain, the weather is so changing that it is often said, “Britain has no climate, only weather.” It has been said that climate is what you expect, but weather is what you get.

Climate: Climate is the description of atmospheric conditions of an area over a long period (say 35 years).
This climate is the average weather of a place over a long period of time. Studies of Indian climate are based on the data relating to the last 100 years. Climate is the composite picture of the changing daily weather conditions. Egypt experiences similar weather day-today and it is said, “Egypt has no weather, only climate.” The basic difference between weather and climate is that weather refers to a short period while the climate refers to a much longer period. We may speak of warm weather of a particular day, but not of a warm climate for that particular day.

Differences between Weather and Climate :

Weather:

1. Weather stands for actual atmospheric conditions for a short period (a day or a week). 
2. The weather changes from day-to-day thus, cannot be generalised.
3. Weather depends upon the dominant element at a particular time say Rainfall, Temperature etc. 
4. Weather is actually present at a place. It is what you get.
5. Every type of weather can occur at one place. 
6. Weather refers to a particular place. 
7. Weather deals with individual elements of weather.
8. Weather is uncertain and we can only forecast  for a short time ahead.

 Climate:

1. Climate is the aggregate of atmospheric conditions for a longer period (say 35 years).
2. The climate is everlasting and static. It  does not change so frequently.
3. Climate is the composite picture of all the elements spread over a longer period.
4. Climate is what you expect. It is arrived at by climatic means or averages.
5. A particular place cannot have all types of climates.
6. Climate refers to a particular area. 
7. It deals with the combination of all the elements of weather. 
8. Climate has a high degree of accuracy and it is similar year after year.

Q.5. Distinguish between the Troposphere and Stratosphere.

Ans:

Troposphere :

1. It is the lowest layer of the atmosphere.
2. Its height varies from 8 kms. at the poles to 20 kms. at the equator. 
3. In this layer the temperature decreases at the rate of 1°C per 165 metres. 
4. It is a zone of convection currents. 
5. Most of the water vapours, clouds and dust particles are found in this layer.
6. Atmospheric disturbances are confined to this zone.
7. Unstable rising air makes weather changes in this layer.

 Stratosphere:

1. It is the second layer of the atmosphere above the earth. 
2. Its height varies from 16 kms. at the equator to 72 km at the poles.
3. In this layer temperatures are very low and fairly constant.
4. It  is  the  non-convective zone of the atmosphere.
5. Clouds, dust particles and water vapours are practically absent in this layer.
6. This zone is free from atmospheric disturbances.
7. Jet stream is a powerful element in this layer.