NCERT Class 11 Geography Fundamental of Physical Geography: Chapter 9 — Atmospheric Circulation and Weather Systems
This chapter, Atmospheric Circulation and Weather Systems, from NCERT's Fundamental of Physical Geography for Class 11, explains the causes of atmospheric pressure differences and the forces governing atmospheric circulation. It details how variations in temperature lead to pressure differences, causing air to move from high to low-pressure areas, creating winds. The chapter discusses the vertical and horizontal distribution of pressure, introducing concepts like isobars and pressure systems (low and high pressure). It also touches upon the global distribution of sea level pressure, including equatorial lows, subtropical highs, subpolar lows, and polar highs. Understanding these concepts is crucial for comprehending weather patterns and climate, aiding students in their CBSE geography studies.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Geography |
| Book | Fundamental of Physical Geography |
| Chapter | Chapter 9 — Atmospheric Circulation and Weather Systems |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 695 |
Learning outcomes
- Understand the concept of atmospheric pressure and its measurement.
- Explain the vertical and horizontal distribution of atmospheric pressure.
- Identify and describe global pressure belts and their seasonal variations.
- Relate pressure differences to wind formation and atmospheric circulation.
- Comprehend the formation of low and high-pressure systems.
Vocabulary
| Word | Meaning |
|---|---|
| Atmospheric Pressure | The weight of a column of air contained in a unit area from the mean sea level to the top of the atmosphere. |
| Isobars | Lines connecting places having equal atmospheric pressure. |
| Milibar | The unit used to express atmospheric pressure. |
| Equatorial Low | An area of low sea level pressure found near the equator. |
| Subtropical Highs | High-pressure areas found around 30° N and 30° S latitude. |
| Subpolar Lows | Low-pressure belts located around 60° N and 60° S latitude. |
| Polar High | High-pressure areas found near the poles. |
| Wind | Air in horizontal motion. |
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Practice questions
- What is atmospheric pressure? Answer: Atmospheric pressure is the weight of a column of air from the mean sea level to the top of the atmosphere, acting on a unit area.
- How does atmospheric pressure change with height? Answer: Atmospheric pressure decreases rapidly with height in the lower atmosphere, approximately by 1 mb for every 10 m increase in elevation.
- What are isobars? Answer: Isobars are lines drawn on a map connecting places that have equal atmospheric pressure.
- Name the major global pressure belts. Answer: The major global pressure belts are the Equatorial Low, Subtropical Highs, Subpolar Lows, and Polar High.
Practice MCQs
Q1. Which instrument is used to measure atmospheric pressure?
Explanation: Barometers, such as mercury or aneroid barometers, are used to measure atmospheric pressure.
Q2. Atmospheric pressure generally decreases with:
Explanation: As altitude increases, the density of air decreases, leading to a reduction in atmospheric pressure.
Q3. What is the primary cause of air motion (wind)?
Explanation: Air moves from areas of high pressure to areas of low pressure, which is the fundamental cause of wind.
Q4. Isobars connect places with:
Explanation: Isobars are lines on a weather map that join points of equal atmospheric pressure.
Q5. The low-pressure area near the equator is known as:
Explanation: The region around the equator experiences consistently low atmospheric pressure due to rising warm air.
Frequently asked questions
What is atmospheric pressure and how is it measured?
Atmospheric pressure is the weight of the air column above a unit area. It is measured using instruments like the mercury barometer or the aneroid barometer.
Why does atmospheric pressure decrease with height?
As you go higher in the atmosphere, there is less air above you, making the air less dense and thus exerting less pressure.
What is the significance of isobars on a weather map?
Isobars connect points of equal atmospheric pressure, helping to visualize pressure gradients and predict wind direction and speed.
What are the main global pressure belts?
The main global pressure belts are the Equatorial Low, Subtropical Highs, Subpolar Lows, and Polar Highs.
How does pressure variation cause wind?
Wind is the horizontal movement of air from an area of high pressure to an area of low pressure, driven by pressure differences.
What is the average sea level pressure?
The average atmospheric pressure at sea level is approximately 1,013.25 millibars (mb).
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NCERT Class 11 Geography — Fundamental of Physical Geography — Chapter 9 — Atmospheric Circulation and Weather Systems. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.