Class 11 Geography NCERT Solutions Chapter 11 Water in the Atmosphere

(i) Name the three types of precipitation.

Answer: The three types of precipitation are:

1. Rain: Liquid water droplets that fall from clouds when the atmosphere is above freezing temperature.
2. Snow: Ice crystals that form in clouds and fall to the ground when the temperature is below freezing.
3. Sleet: Frozen raindrops or small ice pellets that partially melt as they fall and then refreeze upon impact with the ground.

(ii) Explain relative humidity.

Answer: Relative humidity (RH) is a measure of the amount of moisture in the air compared to the maximum amount the air could hold at a specific temperature. It is expressed as a percentage. Warm air can hold more moisture than cold air, so relative humidity indicates how close the air is to being saturated. When RH is 100%, the air is saturated and cannot hold any more moisture. Changes in temperature or moisture content will affect relative humidity.

(iii) Why does the amount of water vapour decrease rapidly with altitude?

Answer: As air rises in the atmosphere, it cools due to decreasing pressure. Cooler air can hold less moisture than warm air. When air reaches its dew point temperature, water vapor begins to condense into water droplets or ice crystals, forming clouds. Therefore, as altitude increases, the temperature decreases, causing the amount of water vapor in the air to decrease rapidly, leading to cloud formation and precipitation.

(iv) How are clouds formed? Classify them.

Answer: Clouds are formed through the process of condensation, where water vapor in the air cools and changes into tiny water droplets or ice crystals that gather around particles in the atmosphere. Clouds are classified into different types based on their appearance and altitude. The main cloud types are:

1. Cirrus: High-altitude, wispy clouds composed of ice crystals.
2. Cumulus: Puffy, cotton-like clouds often associated with fair weather.
3. Stratus: Low-altitude, uniform layers of clouds that often bring overcast skies.
4. Nimbus (Nimbo-): Rain-bearing clouds that can be associated with precipitation.
5. Alto-: Middle-altitude clouds that can be composed of water droplets or ice crystals.
6. Cirro-: Prefix for high-altitude clouds like cirrus.

3. Answer the following questions in about 150 words.

(i) Discuss the salient features of the world distribution of precipitation.

Answer: The world distribution of precipitation exhibits significant variations due to factors such as global air circulation, proximity to water bodies, topography, and prevailing wind patterns. Some salient features of precipitation distribution are as follows:

1. Equatorial Rainforests: Near the equator, regions like the Amazon Basin and Congo Basin experience abundant rainfall throughout the year due to the Intertropical Convergence Zone (ITCZ), where trade winds converge.
2. Tropical Deserts: Tropical deserts like the Sahara and Arabian deserts receive very little rainfall due to the presence of subtropical high-pressure belts. The descending dry air inhibits cloud formation and precipitation.
3. Monsoon Regions: Coastal areas of India, Southeast Asia, and parts of East Africa experience heavy seasonal rainfall due to the shift of the ITCZ and the influence of monsoon winds.
4. Mid-Latitude Regions: Mid-latitude regions, like the United States and Europe, have variable precipitation patterns due to the movement of frontal systems. West coasts of continents often receive more rainfall due to onshore winds and orographic effects.
5. Rain Shadows: Mountain ranges create rain shadows, where one side receives ample rainfall while the other side experiences a rain shadow desert. For example, the western side of the Andes has heavy precipitation, while the eastern side is a desert.
6. Polar Regions: Polar regions have low precipitation due to cold temperatures and limited moisture availability. Most precipitation here occurs in the form of snow.
7. Tropical Cyclone Regions: Coastal areas in tropical cyclone-prone regions, such as the western Pacific and the Indian Ocean, experience intense rainfall during cyclone events.
8. Arctic and Antarctic: Polar regions experience low precipitation in the form of snow due to extremely cold conditions.

These patterns result from the interactions of air masses, global wind belts, and geographic features. Precipitation distribution significantly influences local ecosystems, agriculture, water resources, and climate conditions.

(ii) What are forms of condensation? Describe the process of dew and frost formation.

Answer: Condensation is the process by which water vapor in the air transforms into liquid water or ice crystals. Two common forms of condensation are dew and frost:

Dew Formation: During the night, the ground loses heat through radiation, causing its temperature to drop. When the temperature of the grass, leaves, or other surfaces drops below the dew point temperature, moisture in the air condenses onto these surfaces as small water droplets. This process is called dew formation. Dew forms when the air is near saturation and temperatures are above freezing. It is more common in humid conditions and often occurs on clear, calm nights.

Frost Formation: Frost forms under similar conditions as dew but at temperatures below freezing. When the surface temperature drops below the frost point, water vapor directly changes into ice crystals on surfaces, forming frost. Frost is most common on cold, clear, and calm nights. It can have damaging effects on crops and vegetation.

Both dew and frost formation are influenced by factors like relative humidity, air temperature, and the temperature of the surface. They play essential roles in the local water cycle and affect plant growth and agricultural practices.

Thanks for reading the article on Class 11 Geography NCERT Solutions Chapter 11.