In the context of 'Air Drainage', consider the following statements: 1. It occurs when cold air moves down the slope of hills and mountains. 2. It typically happens during the day when the sun heats the valley bottom. 3. It protects plants from frost damages. Which of the statements given above is/are correct?

Correct Option The correct option is 1 and 3 only. Explanation Air drainage refers to the gravity-driven movement of cold, dense air down the slopes of mountains and hills. This phenomenon is a primary cause of temperature inversion in valley regions, where cold air accumulates at the bottom while warmer air is pushed upwards. Statement-wise Analysis - Statement 1 is Correct: During the night, the slopes of hills and mountains cool rapidly due to terrestrial radiation. The air in contact with these cold surfaces becomes dense and heavy. Under the influence of gravity, this cold air moves down the slope towards the valley bottom. This movement is known as air drainage or katabatic wind. - Statement 2 is Incorrect: Air drainage typically occurs during the night, not the day. During the day, the sun heats the valley slopes, causing the air to expand, become lighter, and move up the slopes (known as anabatic wind or valley breeze). Air drainage requires the cooling of slopes, which happens after sunset. - Statement 3 is Correct: As the cold air drains into the valley bottom, it displaces the warmer air, pushing it upwards to the middle slopes. This creates a zone of warmer temperatures known as the thermal belt. Plants cultivated on these slopes are protected from frost damages that occur in the freezing valley bottom. Consequently, agricultural settlements and orchards are often located on these slopes rather than the valley floor. Key Takeaway Air drainage is a nocturnal phenomenon where cold air flows down slopes (Katabatic wind), causing valley inversion. This protects crops on the slopes (thermal belt) from frost while making the valley bottom susceptible to freezing temperatures.

In the context of 'Air Drainage',… - NCERT Class 11 Geography MCQ

NCERT Class 11 Geography — Chapter 2: Solar radiation, heat balance and temperature

mcqmedium

In the context of 'Air Drainage', consider the following statements:

It occurs when cold air moves down the slope of hills and mountains.
It typically happens during the day when the sun heats the valley bottom.
It protects plants from frost damages.

Which of the statements given above is/are correct?

NCERT textbook question

From NCERT Fundamentals of Physical Geography · Page 7

Options

A2 only
B1, 2 and 3
C1 and 2 only
D1 and 3 only

Did you get this right?

Solution

Correct Option

The correct option is 1 and 3 only.

Explanation

Air drainage refers to the gravity-driven movement of cold, dense air down the slopes of mountains and hills. This phenomenon is a primary cause of temperature inversion in valley regions, where cold air accumulates at the bottom while warmer air is pushed upwards.

Statement-wise Analysis

Statement 1 is Correct: During the night, the slopes of hills and mountains cool rapidly due to terrestrial radiation. The air in contact with these cold surfaces becomes dense and heavy. Under the influence of gravity, this cold air moves down the slope towards the valley bottom. This movement is known as air drainage or katabatic wind.
Statement 2 is Incorrect: Air drainage typically occurs during the night, not the day. During the day, the sun heats the valley slopes, causing the air to expand, become lighter, and move up the slopes (known as anabatic wind or valley breeze). Air drainage requires the cooling of slopes, which happens after sunset.
Statement 3 is Correct: As the cold air drains into the valley bottom, it displaces the warmer air, pushing it upwards to the middle slopes. This creates a zone of warmer temperatures known as the thermal belt. Plants cultivated on these slopes are protected from frost damages that occur in the freezing valley bottom. Consequently, agricultural settlements and orchards are often located on these slopes rather than the valley floor.

Key Takeaway

Air drainage is a nocturnal phenomenon where cold air flows down slopes (Katabatic wind), causing valley inversion. This protects crops on the slopes (thermal belt) from frost while making the valley bottom susceptible to freezing temperatures.

Your note

More from Chapter 2: Solar radiation, heat balance and temperature

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