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If you are looking for NCERT Class 11 Geography Chapter 9: Atmospheric Circulation and Weather Systems Solutions, then this blog is here to help you. This guide provides clear, concise answers to all exercise questions from Chapter 9 of the Fundamentals of Physical Geography textbook. These solutions are designed to help you understand key concepts, prepare for exams, and excel in class discussions. Download the free PDF to revise anytime.
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NCERT Solutions Class 11 Geography Fundamentals of Geography Chapter 9: Atmospheric Circulation and Weather Systems
These NCERT solutions for Class 11 Geography Chapter 9 will help you master the concepts of atmospheric circulation, pressure systems, and weather phenomena. Regular revision of these answers will boost your exam performance.
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:
(a) 700 mb
(b) 1,100 mb
(c) 900 mb
(d) 1,300 mb
(ii) The Inter Tropical Convergence Zone normally occurs:
(a) near the Equator
(b) near the Tropic of Cancer
(c) near the Tropic of Capricorn
(d) near the Arctic Circle
(iii) The direction of wind around a low pressure in northern hemisphere is:
(a) clockwise
(b) perpendicular to isobars
(c) anti-clockwise
(d) parallel to isobars
(iv) Which one of the following is the source region for the formation of air masses?
(a) the Equatorial forest
(b) the Himalayas
(c) the Siberian Plain
(d) the Deccan Plateau
Solutions:
(i) (c) 900 mb
Air pressure decreases with altitude. At 1 km above the surface, pressure typically drops by about 100 mb from the surface value of 1,000 mb, resulting in approximately 900 mb.
(ii) (a) near the Equator
The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt where trade winds converge, typically located near the Equator due to intense solar heating.
(iii) (c) anti-clockwise
In the Northern Hemisphere, the Coriolis force deflects winds to the right, causing them to blow anticlockwise around low-pressure systems.
(iv) (c) the Siberian Plain
Air masses form over large, uniform surfaces like the Siberian Plain, which provides stable conditions for developing distinct temperature and humidity characteristics.
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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?
Solution: The unit for measuring pressure is millibar (mb). Station-level pressure is reduced to sea level to standardise measurements, eliminating altitude variations for accurate comparison 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?
Solution: The Coriolis force deflects winds to the right in the Northern Hemisphere, turning winds from subtropical high pressure toward the equator into north-easterlies in the tropics.
(iii) What are the geostrophic winds?
Solution: Geostrophic winds are winds blowing parallel to isobars at high altitudes, where the pressure gradient force balances the Coriolis force, unaffected by surface friction.
(iv) Explain the land and sea breezes.
Solution: Land and sea breezes are local winds caused by differential heating. During the day, land heats faster, creating sea breezes; at night, land cools faster, producing land breezes.
3. Answer the Following Questions in About 150 Words
(i) Discuss the factors affecting the speed and direction of wind.
Solution: The speed and direction of wind are influenced by several factors. The pressure gradient force is the primary driver, with stronger gradients causing faster winds. The Coriolis force, due to Earth’s rotation, deflects winds to the right in the Northern Hemisphere and left in the Southern Hemisphere, shaping wind direction. Friction with the Earth’s surface, significant in the lower atmosphere, slows winds and alters their direction, especially over rough terrain. Centrifugal force affects winds in curved paths, such as around cyclones. Altitude also plays a role; winds are faster at higher altitudes due to reduced friction. Additionally, local topography, like mountains or valleys, can channel or redirect winds, creating local wind patterns. These factors interact to determine wind characteristics, influencing weather systems and atmospheric circulation globally, as seen in trade winds and jet streams.
(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?
Solution: [Diagram Description: A simplified diagram would show three cells per hemisphere—Hadley, Ferrel, and Polar cells. The Hadley cell has rising air at the equator (ITCZ) and sinking air at 30° N/S (subtropical highs). The Ferrel cell operates between 30° and 60° latitudes, and the Polar cell between 60° and the poles, with trade winds, westerlies, and polar easterlies.]
Subtropical high-pressure systems form around 30° N and S due to the Hadley cell dynamics. Intense solar heating at the equator causes warm air to rise, creating low pressure (ITCZ). This air cools and sinks at approximately 30° latitudes, forming high-pressure zones. The Coriolis force deflects descending air, reinforcing these stable, dry regions. Additionally, global heat distribution and the Earth’s rotation contribute to the consistent positioning of these high-pressure belts, which influence trade winds and desert formation.
(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?
Solution: Tropical cyclones originate over warm seas (temperatures above 26.5°C) because they require significant heat and moisture for formation. Warm ocean waters provide latent heat through evaporation, fueling the cyclone’s low-pressure centre and driving convection. Seas offer a uniform, frictionless surface, allowing sustained wind convergence. Land disrupts this process, preventing cyclone formation.
Torrential rains and high-velocity winds occur in the eyewall, the region surrounding the calm eye of the cyclone. The eyewall experiences intense upward air motion, leading to condensation and heavy rainfall. Strong pressure gradients near the centre generate high-velocity winds, spiralling inward due to the Coriolis force. The eyewall’s compact structure concentrates energy, making it the most destructive part of the cyclone.
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Download NCERT Solutions Class 11 Geography Fundamentals of Physical Geography Chapter 9: Atmospheric Circulation and Weather Systems
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