CBSE Class 11 Geography: Chapter 10 Atmospheric Circulation and Weather Systems NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

This chapter, "Atmospheric Circulation and Weather Systems," delves into the fundamental concepts of atmospheric pressure, wind, and the forces that govern their movement. It explains the relationship between pressure gradients and wind direction, introducing the Coriolis effect and its influence on global wind patterns. The solutions cover various weather systems, including air masses and the Inter Tropical Convergence Zone (ITCZ). Students will learn about land and sea breezes and the factors influencing wind speed and direction. These NCERT Solutions provide clear explanations and step-by-step answers to help students grasp complex meteorological concepts, aiding in their exam preparation and understanding of Earth's dynamic atmosphere.

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Quick info

Board	CBSE
Class	Class 11
Subject	Fundamental of Physical Geography
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 10

Chapter summary

Chapter 10, "Atmospheric Circulation and Weather Systems," focuses on the mechanics of atmospheric movement. It covers the measurement and reduction of atmospheric pressure, the role of pressure gradient and Coriolis forces in determining wind direction and speed, and the formation of geostrophic winds. The chapter also explains local wind phenomena like land and sea breezes and the characteristics of air masses. These NCERT Solutions offer comprehensive answers to questions related to these topics, reinforcing key concepts for students.

Learning outcomes

Understand the units and measurement of atmospheric pressure.
Explain the reasons for reducing station-level pressure to sea level.
Describe the formation and characteristics of geostrophic winds.
Analyze the factors influencing wind speed and direction.
Differentiate between land and sea breezes.
Identify the source regions for air masses.

Topics covered

Paper topics

Atmospheric Pressure
Pressure Gradient Force
Coriolis Effect
Wind Speed and Direction
Geostrophic Winds
Air Masses
Source Regions of Air Masses
Inter Tropical Convergence Zone (ITCZ)
Land and Sea Breezes
Weather Systems

Important topics

Factors affecting wind speed and direction
Role of Pressure Gradient Force and Coriolis Effect
Geostrophic Winds
Air Mass Formation and Source Regions
ITCZ Location and Significance

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Questions and Solutions

Multiple Choice Questions

(i) If the surface air pressure is 1,000 mb, the air pressure at 1 km above the surface will be:

(a) 700 mb

(b) 1,100 mb

(d) 1,300 mb

Solution: Air pressure decreases significantly with increasing altitude because there is less air above exerting pressure. While the exact decrease depends on temperature and other factors, a general rule of thumb is a drop of about 10 mb for every 100 meters. Therefore, at 1 km (1000 meters) above the surface, the pressure would decrease by approximately 100 mb from the surface pressure. Given the surface pressure is 1,000 mb, the pressure at 1 km would be around 900 mb. Thus, option (c) is the most appropriate answer.

(ii) The Inter Tropical Convergence Zone normally occurs:

(a) near the Equator

(b) near the Tropic of Cancer

(d) near the Arctic Circle

Solution: The Inter Tropical Convergence Zone (ITCZ) is a low-pressure belt that encircles the Earth near the Equator. It is formed by the convergence of the northeast and southeast trade winds. This zone shifts seasonally, but its normal position is close to the Equator.

(iii) The direction of wind around a low pressure in northern hemisphere is:

(a) clockwise

(b) perpendicular to isobars

(d) parallel to isobars

Solution: In the Northern Hemisphere, the Coriolis effect deflects moving air to the right. Around a low-pressure system (where air flows inwards towards the center), this deflection causes the winds to circulate in an anti-clockwise direction. Conversely, around a high-pressure system, the circulation is clockwise.

(iv) Which one of the following is the source region for the formation of air masses?

(a) the Equatorial forest

(b) the Himalayas

(d) the Deccan Plateau

Solution: An air mass forms when air remains stationary or moves slowly over a large, uniform area for an extended period, acquiring the temperature and humidity characteristics of that surface. The Siberian Plain, a vast, flat, and cold region, is an ideal source region for the formation of cold, dry continental polar air masses.

1. What is the unit used in measuring pressure? Why is the pressure measured at station level reduced to the sea level in preparation of weather maps?

Solution: The atmospheric pressure is commonly measured in units of millibars (mb). The average atmospheric pressure at sea level is approximately 1,013.2 millibars. Pressure measured at a station is reduced to sea level to eliminate the influence of altitude. This standardization is crucial for creating accurate weather maps, as it allows for direct comparison of pressure conditions across different locations, irrespective of their elevation above sea level.

2. While the pressure gradient force is from north to south, i.e. from the subtropical high pressure to the equator in the northern hemisphere, why are the winds north easterlies in the tropics.

Solution: The pressure gradient force acts from the subtropical high-pressure belt (north) towards the equatorial low-pressure belt (south) in the Northern Hemisphere. However, the Earth's rotation introduces the Coriolis force, which deflects moving objects, including winds, to the right in the Northern Hemisphere. This deflection causes the winds that would otherwise blow directly from north to south to become north-easterlies, blowing from the northeast towards the southwest.

3. What are the geostrophic winds?

Solution: Geostrophic winds are hypothetical winds that result from a perfect balance between two opposing forces: the pressure gradient force and the Coriolis force. The pressure gradient force pushes air from areas of high pressure to areas of low pressure, while the Coriolis force deflects this moving air due to the Earth's rotation. When these two forces are equal in magnitude and opposite in direction, the wind flows parallel to the isobars (lines of equal pressure).

4. Explain the land and sea breezes.

Solution: Land and sea breezes are local winds caused by differential heating of land and water. Sea Breeze: During the day, land heats up faster than the sea. The warmer air over the land rises, creating a low-pressure area. Cooler, denser air from over the sea moves inland to replace it, creating a sea breeze. Land Breeze: At night, the land cools down faster than the sea. The air over the sea is now warmer, rises, and creates a low-pressure area. Cooler air from the land moves out towards the sea to fill this space, creating a land breeze.

5. Discuss the factors affecting the speed and direction of wind.

Solution: The speed and direction of wind are influenced by several factors:

Pressure Gradient Force (PGF): This is the primary driving force behind wind. It is the force exerted by differences in air pressure over a distance. A steeper pressure gradient (larger pressure difference over a shorter distance) results in a stronger PGF and thus, higher wind speeds. The PGF directs wind from high pressure to low pressure.
Coriolis Force: Due to the Earth's rotation, moving objects (including air) are deflected from their intended path. In the Northern Hemisphere, this deflection is to the right of the direction of motion, and in the Southern Hemisphere, it is to the left. The Coriolis force increases with latitude and with the speed of the wind. It does not affect wind speed but significantly alters its direction, leading to winds blowing parallel to isobars in the upper atmosphere (geostrophic winds).
Friction: Friction is a force that opposes motion and is significant near the Earth's surface, especially over land with obstacles like trees and buildings. It slows down the wind speed, thereby reducing the effect of the Coriolis force. This is why winds near the surface do not blow exactly parallel to the isobars but cross them at an angle, moving from higher to lower pressure. Over the oceans, friction is much less significant.

The interplay of these forces determines the final speed and direction of the wind. In the upper atmosphere, where friction is negligible, the wind blows parallel to the isobars (geostrophic wind). Near the surface, friction causes the wind to slow down and turn across the isobars towards the low-pressure area.

Common mistakes

Confusing wind direction around low-pressure systems in different hemispheres.
Not fully accounting for the Coriolis effect when explaining wind patterns.
Overlooking the role of differential heating in creating land and sea breezes.

Revision tips

Focus on understanding the interplay between pressure gradient force and Coriolis force.
Draw diagrams to visualize wind circulation around pressure systems.
Relate theoretical concepts like geostrophic winds to real-world weather phenomena.
Memorize the key characteristics of air masses and their source regions.

Practice MCQs

Q1. If the surface air pressure is 1,000 mb, what is the approximate air pressure at 1 km above the surface?

Q2. Where is the Inter Tropical Convergence Zone (ITCZ) normally located?

Q3. What is the typical direction of wind circulation around a low-pressure system in the Northern Hemisphere?

Q4. Which of the following is a common source region for the formation of air masses?

Q5. Geostrophic winds are a result of the balance between which two forces?

Frequently asked questions

What are the main units used to measure atmospheric pressure?

Atmospheric pressure is primarily measured in millibars (mb). The average atmospheric pressure at sea level is approximately 1,013.2 millibars.

Why is atmospheric pressure reduced to sea level for weather maps?

Pressure measured at a specific station is reduced to sea level to eliminate the effect of altitude. This standardization allows for accurate comparison of pressure across different locations, regardless of their elevation.

What is a geostrophic wind?

A geostrophic wind is a theoretical wind that arises when the pressure gradient force pushing air from high to low pressure is perfectly balanced by the Coriolis force, which deflects the wind due to Earth's rotation.

How do land and sea breezes form?

Sea breezes occur during the day when land heats up faster than the sea, causing air to flow from the cooler sea to the warmer land. Land breezes occur at night when the land cools faster than the sea, reversing the airflow.

What is the significance of the Inter Tropical Convergence Zone (ITCZ)?

The ITCZ is a low-pressure belt near the Equator where the trade winds from both hemispheres converge. It is characterized by rising air, cloud formation, and often heavy rainfall.

What are air masses and where do they form?

Air masses are large bodies of air with relatively uniform temperature and humidity. They form over extensive, uniform surfaces like the Siberian Plain (for cold, dry air) or tropical oceans (for warm, moist air).

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