NCERT Solutions For Class 11 Geography Chapter 9 Atmospheric Circulation and Weather Systems - 2025-26

1. Multiple choice questions.

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

• 700 mb
• 1,100 mb
• 900 mb
• 1,300 mb

Answer: 900 mb.

ii. The Inter Tropical Convergence Zone normally occurs:

• near the Equator
• near the Tropic of Cancer
• near the Tropic of Capricorn
• near the Arctic Circle

Answer: near the Equator.

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

• clockwise
• perpendicular to isobars
• anticlockwise
• parallel to isobars

Answer: anticlockwise.

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

• the Equatorial forest
• the Himalayas
• the Siberian Plain
• the Deccan Plateau

Answer: the Siberian Plain.

2. Answer the following questions in about 30 words.

i. 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?

Answer: Atmospheric pressure is measured in millibars (mb). Pressure at station level is reduced to sea level to remove the effect of altitude, enabling comparison between different locations on weather maps.

ii. 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?

Answer: Due to the Coriolis force, winds moving from subtropical high pressure to the equator are deflected to the right in the Northern Hemisphere, resulting in the north easterly direction of the trade winds.

iii. What are the geostrophic winds?

Answer: Geostrophic winds are upper-level winds that flow parallel to isobars, resulting from a balance between the pressure gradient force and the Coriolis force, unaffected by surface friction.

iv. Explain the land and sea breezes.

Answer: During the day, land heats up faster than sea, causing air above to rise and cool air from the sea to move in (sea breeze). At night, land cools faster, so air flows from land to sea (land breeze).

3. Answer the following questions in about 150 words.

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

Answer: The speed and direction of wind are influenced by three main forces: pressure gradient force, Coriolis force, and frictional force.

The pressure gradient force causes wind to move from high to low pressure areas. The Coriolis force, caused by Earth’s rotation, deflects wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Its influence increases with higher wind speed and latitude. Surface friction slows down the wind and changes its direction, being most effective near the ground and diminishing with altitude.

The combination of these forces results in various wind patterns, such as geostrophic winds in the upper atmosphere and surface winds that respond to all the forces. Wind direction also alters around pressure systems: in the Northern Hemisphere, winds blow anticlockwise around lows (cyclones) and clockwise around highs (anticyclones).

ii. Draw a simplified diagram to show the general circulation of the atmosphere over the globe. What are the possible reasons for the formation of subtropical high pressure over 30°N and S latitudes?

Answer: (Refer to Figure 9.6 in the textbook for the diagram.) The subtropical high-pressure belts at about 30°N and 30°S are formed by the sinking air from the Hadley Cells. After rising at the Inter Tropical Convergence Zone (ITCZ), warm, moist air cools and moves polewards in the upper atmosphere.

At around 30° latitude, this air descends, increasing pressure at the surface and forming a zone of high pressure. The combination of atmospheric heating, Earth's rotation, and the convergence-divergence of air currents leads to these subtropical highs, which are largely responsible for the creation of deserts in these regions.

iii. Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?

Answer: Tropical cyclones originate over the seas because warm ocean surfaces (temperature above 27°C) provide the necessary moisture and heat energy. This results in rapid rising of air, reducing surface pressure and triggering cyclone development. The Coriolis force is also needed for rotation, thus cyclones do not form near the equator.

Torrential rains and high-velocity winds blow in the eye wall region surrounding the calm center (eye) of the cyclone. Here, the pressure gradient is steepest, causing the most intense winds and rainfall as moist air ascends rapidly, cools, and condenses, releasing energy.

Understanding Atmospheric Circulation and Weather Systems

Mastering Atmospheric Circulation and Weather Systems is key to scoring well in Geography. This chapter explains vital concepts like pressure belts, planetary winds, and the origin of cyclones for CLass 11 exams and beyond.

Focus on the roles of air masses, fronts, and wind forces to understand changing weather patterns. Practicing NCERT questions on these topics strengthens your foundation and boosts your confidence for board exam preparations.

For top marks, review the general circulation model, monsoon winds, and types of cyclones. Keep revising diagrams and key terms to enhance memory retention and improve your Geography exam strategy.

CBSE Class 11 Geography Chapter-wise NCERT Solutions

CBSE Class 11 Geography Study Materials