Consider the diagram given below : The above diagram represents the pressure conditions of three different places, viz., A, B and C. Which of the following is the correct direction of movement of winds ?

1. Basics of Atmospheric Pressure (basic)

Imagine standing at the bottom of a deep swimming pool; you can feel the weight of the water pressing against your body from all sides. We live in a similar way at the bottom of a vast "ocean" of air. Atmospheric pressure is defined as the weight of a column of air contained in a unit area, extending from the mean sea level all the way to the top of the atmosphere FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Chapter 9, p.76. Because gravity pulls air molecules toward the Earth, the atmosphere is densest and heaviest at the surface. This is why our bodies are constantly subjected to significant pressure, though we rarely notice it because our internal fluids exert an equal outward pressure.

To quantify this weight, meteorologists use an instrument called a barometer (either mercury-based or the portable aneroid type). The standard units you will encounter in your preparation are millibars (mb) and pascals (Pa). While the SI unit is the Pascal, the practical unit for weather reporting is the millibar, where 1 mb equals 100 Pa Science, Class VIII . NCERT(Revised ed 2025), Pressure, Winds, Storms, and Cyclones, p.87. At sea level, the average atmospheric pressure is approximately 1013.25 mb. Anything significantly lower than 1000 mb usually indicates a weather disturbance or "depression" Exploring Society: India and Beyond, Social Science-Class VII . NCERT(Revised ed 2025), Understanding the Weather, p.35.

One of the most critical concepts to grasp is that atmospheric pressure is not uniform. It varies based on altitude and temperature. As you move to higher altitudes, such as the Himalayas, the air becomes rarefied (thinner) and the column of air above you is shorter, leading to a decrease in pressure. This is why mountaineers and army personnel at high-altitude posts like Khardung La must acclimatize to avoid breathlessness Exploring Society: India and Beyond, Social Science-Class VII . NCERT(Revised ed 2025), Understanding the Weather, p.35. These spatial differences in pressure are the fundamental reason air begins to move, seeking to balance the scales by flowing from high-pressure zones to low-pressure zones.

Feature	Sea Level	High Altitude (Mountains)
Air Density	High (Compressed by gravity)	Low (Rarefied)
Average Pressure	~1013.25 mb	Significantly lower (e.g., < 500 mb)
Oxygen Availability	Abundant	Lower (causing breathlessness)

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Chapter 9: Atmospheric Circulation and Weather Systems, p.76; Science, Class VIII . NCERT(Revised ed 2025), Pressure, Winds, Storms, and Cyclones, p.87; Exploring Society: India and Beyond, Social Science-Class VII . NCERT(Revised ed 2025), Understanding the Weather, p.35; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Chapter 23: Pressure Systems and Wind System, p.304

2. Temperature-Pressure Relationship (basic)

To understand why winds blow, we must first understand the relationship between temperature and atmospheric pressure. At its most basic level, think of the atmosphere as a collection of air molecules. When these molecules are heated by the sun, they gain energy and start moving more vigorously, pushing away from one another. This causes the air to expand, making the air parcel less dense and lighter than the surrounding air Physical Geography by PMF IAS, Vertical Distribution of Temperature, p.297.

Because this heated air is now lighter, it begins to rise. Imagine a hot air balloon; the air inside is heated, becomes less dense, and lifts the balloon upward. At the Earth's surface, this rising motion leaves behind fewer air molecules, which means there is less "weight" pressing down on the ground. In meteorological terms, we say the atmospheric pressure has decreased. This is why intensely heated areas, like the Equator, are characterized by Thermal Lows Physical Geography by PMF IAS, Pressure Systems and Wind System, p.314.

Conversely, when air is cooled (such as over the icy poles or during a cold winter night), the molecules lose energy and huddle closer together. The air contracts, becomes denser, and begins to sink. As this heavy air accumulates near the surface, it exerts more force on the ground, creating a Thermal High. This fundamental inverse relationship—where high temperatures lead to low pressure and low temperatures lead to high pressure—is the engine that drives global wind patterns Geography of India, Majid Husain, Climate of India, p.1.

Condition	Molecular Action	Density	Vertical Movement	Pressure Result
Heating	Expansion	Decreases (Lighter)	Rising (Convection)	Low Pressure
Cooling	Contraction	Increases (Heavier)	Sinking (Subsidence)	High Pressure

Sources: Physical Geography by PMF IAS, Vertical Distribution of Temperature, p.297; Physical Geography by PMF IAS, Pressure Systems and Wind System, p.314; Geography of India, Majid Husain, Climate of India, p.1

3. Global Pressure Belts and Cells (intermediate)

To understand how the world breathes, we must look at the Global Pressure Belts. While we might expect air to simply flow from the hot Equator to the cold Poles, the Earth’s rotation (Coriolis force) and differential heating break this flow into three distinct cells in each hemisphere. These cells create a see-saw of high and low pressure across the globe. Physical Geography by PMF IAS, Jet streams, p.385

Near the Equator (10° N to 10° S), intense solar heating causes air to expand and rise, creating the Equatorial Low Pressure Belt. This zone is famously known as the Doldrums because the rising air leaves the surface with very little horizontal wind, often leaving historical sailors stranded. This is also the Intertropical Convergence Zone (ITCZ), where trade winds from both hemispheres meet. GC Leong, Climate, p.139

As this warm air rises, it cools and eventually sinks around 30° N and 30° S, creating the Sub-Tropical High Pressure Belts. This sinking air is dry and calm, leading to the formation of most of the world's great deserts. Further toward the poles, at 60° N and 60° S, we find the Sub-polar Lows, where warmer air from the subtropics meets cold polar air and is forced to rise. Finally, the extreme cold at the poles creates the Polar Highs. NCERT Class XI Fundamentals of Physical Geography, Atmospheric Circulation and Weather Systems, p.77

These belts are linked by three atmospheric loops or "cells":

Cell Name	Location	Origin Type	Mechanism
Hadley Cell	Equator to 30°	Thermal	Driven by solar heating at the Equator.
Ferrel Cell	30° to 60°	Dynamic	Driven by the friction/rotation of the other two cells.
Polar Cell	60° to Poles	Thermal	Driven by extreme cooling at the Poles.

Physical Geography by PMF IAS, Pressure Systems and Wind System, p.317

Sources: Physical Geography by PMF IAS, Jet streams, p.385; Certificate Physical and Human Geography, GC Leong, Climate, p.139; FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT), Atmospheric Circulation and Weather Systems, p.77; Physical Geography by PMF IAS, Pressure Systems and Wind System, p.317

4. Forces Affecting Wind Direction (intermediate)

Wind is not just air moving randomly; it is a precise response to physical forces. Think of it as nature’s attempt to fix an imbalance. When there is a difference in atmospheric pressure between two regions, air is set in motion. This horizontal movement of air is what we call wind. However, the path a wind takes from point A to point B is rarely a straight line because it is governed by a delicate tug-of-war between three primary forces: the Pressure Gradient Force, the Coriolis Force, and Friction FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Chapter 9, p.78.

The Pressure Gradient Force (PGF) is the engine of wind. It is generated by the difference in pressure between high and low-pressure areas. The PGF always acts perpendicular to the isobars (lines of equal pressure), pushing air directly from high pressure toward low pressure. The closer the isobars are to each other, the steeper the "slope" (gradient), and the faster the wind blows. Without any other forces, wind would simply flow in a straight line to fill the low-pressure void FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Chapter 9, p.79.

However, the Earth is rotating, which introduces the Coriolis Force. This is an apparent force that deflects the wind's path—to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. A crucial detail for your preparation is its variation: the Coriolis force is zero at the equator and reaches its maximum at the poles Physical Geography by PMF IAS, Chapter 23, p.309. It is also directly proportional to wind speed; the faster the wind, the stronger the deflection. This is why tropical cyclones cannot form exactly at the equator—there isn't enough Coriolis force to create the necessary rotation Physical Geography by PMF IAS, Chapter 30, p.356.

Finally, near the Earth's surface, Frictional Force acts as a "brake." It resists the motion of the air, slowing it down. Because friction reduces wind speed, it also indirectly reduces the Coriolis deflection. This is why surface winds often cross isobars at an angle, rather than blowing parallel to them. Friction is highest over rugged land surfaces and minimal over smooth oceans, and its influence generally fades away at altitudes above 1-3 km Physical Geography by PMF IAS, Chapter 23, p.307.

Force	Primary Role	Key Characteristic
Pressure Gradient	Initiates movement	Acts from High to Low pressure; perpendicular to isobars.
Coriolis Force	Changes direction	Zero at Equator, Max at Poles; increases with wind speed.
Frictional Force	Reduces speed	Strongest at the surface; negligible over oceans and at high altitudes.

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Chapter 9: Atmospheric Circulation and Weather Systems, p.78-79; Physical Geography by PMF IAS, Chapter 23: Pressure Systems and Wind System, p.306-309; Physical Geography by PMF IAS, Chapter 30: Tropical Cyclones, p.356

5. Cyclones, Anticyclones, and Local Winds (intermediate)

To understand how our atmosphere 'breathes,' we must look at Cyclones and Anticyclones. At its simplest, a cyclone is a system where the atmospheric pressure is lowest at the center, causing surrounding air to rush inward. Because of the Coriolis force, this inward-moving air doesn't travel in a straight line; it spirals counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Chapter 9, p. 82. This rising air cools and condenses, which is why cyclones are almost always associated with clouds, rain, and stormy weather. Conversely, an anticyclone is a high-pressure system where air sinks from above and spreads outward (diverges) from the center. This sinking air inhibits cloud formation, leading to the 'fine weather,' clear skies, and calm conditions typical of anticyclones Certificate Physical and Human Geography, GC Leong (3rd ed.), Climate, p. 143.

On a much smaller and more personal scale, we experience Local Winds like Land and Sea breezes. These are driven by the fact that land and water heat up and cool down at different rates—a concept known as differential heating. During the day, the land heats up rapidly, causing the air above it to rise and create a Local Low Pressure. The sea remains relatively cool (High Pressure), so a refreshing Sea Breeze blows from the water toward the land to fill that gap Physical Geography by PMF IAS, Manjunath Thamminidi (1st ed.), Pressure Systems and Wind System, p. 321. At night, the process reverses: the land loses heat quickly while the sea stays warm, creating a Land Breeze that blows from the shore out to sea.

Feature	Cyclone (Low Pressure)	Anticyclone (High Pressure)
Vertical Air Motion	Rising (Ascending)	Sinking (Subsiding)
Surface Wind Direction	Inward (Convergence)	Outward (Divergence)
NH Rotation	Counter-Clockwise	Clockwise
Weather Type	Stormy, Cloudy, Rainy	Fair, Clear Skies, Calm

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Atmospheric Circulation and Weather Systems, p.82; Certificate Physical and Human Geography, GC Leong (Oxford University press 3rd ed.), Climate, p.141-143; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Pressure Systems and Wind System, p.321

6. The Pressure Gradient Force (PGF) (exam-level)

Imagine you are holding a balloon: the air inside is under high pressure, while the air outside is at lower pressure. When you let go of the neck, the air rushes out instantly. This movement is the essence of Wind—the horizontal motion of air across the Earth's surface. The engine that powers this movement is the Pressure Gradient Force (PGF). Simply put, differences in atmospheric pressure produce a force that tries to balance the scales by pushing air from where there is 'too much' (High Pressure) to where there is 'not enough' (Low Pressure) FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI, Chapter 9, p. 78.

The direction of this force is always perpendicular to the isobars (lines connecting points of equal pressure), acting directly from high-pressure centers toward low-pressure centers Physical Geography by PMF IAS, Chapter 23, p. 306. For instance, if you have a high-pressure cell at 1020 mb (Point B) surrounded by lower pressure zones at 1012 mb (Points A and C), the PGF will initiate air movement outward from B toward both A and C. It is the fundamental 'starting gun' for all atmospheric circulation; without a pressure gradient, the air would remain stagnant.

The velocity of the wind is dictated by how 'steep' this gradient is. We measure this by looking at the spacing of isobars on a weather map. The rate of change of pressure with respect to distance determines the speed: the more rapidly pressure drops over a short distance, the stronger the force Physical Geography by PMF IAS, Chapter 23, p. 304.

Isobar Spacing	Pressure Gradient	Wind Velocity
Close together	Strong / Steep	High (Strong Winds)
Far apart	Weak / Gentle	Low (Light Breezes)

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Chapter 9: Atmospheric Circulation and Weather Systems, p.78; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Chapter 23: Pressure Systems and Wind System, p.304, 306

7. Solving the Original PYQ (exam-level)

Now that you have mastered the concept of Pressure Gradient Force (PGF), this question serves as a perfect application of that fundamental principle. As we discussed, wind is simply the horizontal movement of air seeking to rectify an imbalance in atmospheric pressure. According to FUNDAMENTALS OF PHYSICAL GEOGRAPHY (NCERT), air always moves from areas of high pressure toward areas of low pressure. To solve this, you simply need to identify the "source" (the highest value) and the "sinks" (the lower values) in the provided diagram.

Looking closely at the values, Place B stands out with a pressure of 1020 mb, which is higher than both Place A (1016 mb) and Place C (1012 mb). Thinking like a coach: if B is the high-pressure center, the pressure gradient will act outward from B in all directions where pressure is lower. Therefore, the wind must Blow from B towards A and C to equalize the density of air molecules. This direct movement from a central high-pressure zone to surrounding lower-pressure zones makes Option (A) the only logically sound choice.

UPSC often uses distractors like Option (C) or (D) to test if you understand that wind flow is determined by the net pressure gradient. Option (C) suggests a sequence (B to A and A to C), which might look tempting because 1020 > 1016 > 1012. However, in a localized system, the air at the highest point (B) flows simultaneously toward all surrounding lower points. Option (D) suggests a reciprocal flow, which is physically impossible because wind cannot blow "uphill" against a pressure gradient. As noted in Physical Geography by PMF IAS, the velocity and direction are dictated by the steepness of this gradient, making the flow from the 1020 mb peak toward the lower 1016 mb and 1012 mb valleys the natural path of least resistance.