Atmospheric Circulation – UGC NET Geography Notes

Atmospheric Circulation: Atmospheric circulation is the large-scale movement of air that regulates the Earth’s climate by redistributing heat from the equator to the poles. Driven by solar radiation, pressure belts, and the Coriolis effect, it consists of three primary cells, namely, Hadley, Ferrel, and Polar cells which influence global wind patterns like trade winds, westerlies, and polar easterlies. This topic is crucial in UGC NET Geography, as it explains monsoons, jet streams, cyclones, and climate variability, making it essential for aspirants aiming to excel in climatology and physical geography.

What is Atmospheric Circulation?

Atmospheric circulation is the large-scale movement of air that distributes heat and moisture across the Earth, maintaining global climate balance. Here are its features:

• In physical geography, atmospheric circulation is crucial for understanding climate zones, weather patterns, and monsoons.
• It influences temperature distribution, precipitation, and ocean currents, shaping ecosystems and human activities worldwide.

Three Cell Model of Atmospheric Circulation

The Three-Cell Model explains global wind circulation, driven by solar heating, Coriolis force, and pressure gradients. It consists of three key cells influencing weather patterns, climate zones, and monsoons, which is a crucial topic for UGC NET Geography.

1. Hadley Cell – Trade Winds and Equatorial Convection

Operating between 0°–30° latitude, the Hadley Cell drives equatorial convection as warm air rises at the ITCZ, moves poleward, cools, and sinks at 30° latitude, creating subtropical high-pressure zones. This forms trade winds, influencing monsoons and tropical climates.

2. Ferrel Cell – Westerlies and Mid-Latitude Weather

Located between 30°–60° latitude, the Ferrel Cell transports air poleward, generating westerlies that drive temperate zone cyclones and storm systems, impacting North America and Europe.

3. Polar Cell – Polar Easterlies and Cold Air Movement

Extending from 60° to the poles, the Polar Cell pushes cold, dense air equatorward, forming polar easterlies. Its interaction with westerlies creates polar fronts, storms, and Arctic climate variability.

Major Wind Systems in Atmospheric Circulation

Global wind systems play a crucial role in climate regulation, weather patterns, and ocean currents. The three primary wind belts: Trade Winds, Westerlies, and Polar Easterlies, are driven by Earth’s rotation, pressure gradients, and solar heating.

1. Trade Winds – Impact on Monsoons and Tropical Weather

The Trade Winds blow from subtropical high-pressure zones (30° latitude) toward the equator (ITCZ), moving from northeast in the Northern Hemisphere and southeast in the Southern Hemisphere due to the Coriolis effect. These winds:

• Drive tropical cyclones, hurricanes, and typhoons.
• Influence monsoon patterns, especially in South Asia.
• Power ocean currents like the North and South Equatorial Currents, affecting marine ecosystems.

2. Westerlies – Influence on Mid-Latitude Cyclones

The Westerlies blow from 30°–60° latitude, moving west to east. Stronger in winter, they are responsible for:

• Mid-latitude cyclones that impact North America, Europe, and Asia.
• Steering jet streams, affecting weather variability.
• Driving ocean currents like the Gulf Stream, influencing climate in Europe.

3. Polar Easterlies – Role in Extreme Weather Near the Poles

The Polar Easterlies originate from high-pressure polar regions (90° latitude) and move toward lower latitudes (60°). They:

• Cause cold waves and Arctic storms.
• Form the polar vortex, leading to extreme winter conditions.
• Interact with westerlies, creating polar fronts and storm activity.

Also Check: Geomorphic Cycle – UGC NET Geography Notes

Pressure Belts and Their Role in Atmospheric Circulation

Pressure belts are global zones of high and low pressure that drive wind circulation, monsoons, and climate patterns. Formed due to Earth’s rotation and uneven heating, they influence global wind systems.

1. Equatorial Low (0° Latitude) – Intense Convection and Rainfall

• Located at the Intertropical Convergence Zone (ITCZ).
• Warm air rises, creating low pressure and heavy rainfall (e.g., Amazon Rainforest).
• Drives trade winds and monsoon formation.

2. Subtropical High (30° Latitude) – Dry and Stable Conditions

• Sinking air creates high pressure, leading to dry climates and deserts (e.g., Sahara).
• Generates trade winds (toward the equator) and westerlies (toward mid-latitudes).

3. Subpolar Low (60° Latitude) – Storm Formation

• Rising air from westerlies and polar easterlies creates low pressure.
• Drives storm systems and mid-latitude cyclones (e.g., North Atlantic storms).

4. Polar High (90° Latitude) – Extreme Cold and Dense Air

• Sinking cold air forms high-pressure zones at the poles.
• Generates polar easterlies, leading to Arctic and Antarctic weather extremes.

Pressure Belts and Global Wind Patterns

• Low-pressure belts (Equatorial, Subpolar) → Warm air rises, creating clouds and precipitation.
• High-pressure belts (Subtropical, Polar) → Air sinks, leading to dry and stable weather.

These belts drive Trade Winds, Westerlies, and Polar Easterlies, shaping global weather and climate.

Jet Streams and Their Impact on Climate

Jet streams are fast-moving, narrow air currents in the upper troposphere, driven by temperature gradients and Earth’s rotation.

Types of Jet Streams

• Polar Jet Stream (30°–60° latitude): Strongest in winter, it steers mid-latitude cyclones, cold waves, and storm tracks.
• Subtropical Jet Stream (20°–30° latitude): Influences monsoons, El Niño events, and upper-level weather patterns.

Influence on Weather Systems, Monsoons, and Cyclones

• Guides cyclones and storms, impacting rainfall and extreme weather.
• Controls monsoon onset and withdrawal, crucial for South Asian rainfall.
• Disruptions (El Niño, La Niña) affect global temperature and precipitation patterns.

Also Check: Concept of Continental Drift Theory

Monsoons and Atmospheric Circulation

Monsoons are seasonal wind shifts caused by differential heating of land and ocean, driven by atmospheric circulation and pressure belts. They are essential for agriculture, water availability, and climate stability, particularly in South Asia.

How Atmospheric Circulation Affects Monsoons in South Asia?

Monsoons are always affected by atmospheric circulations. Here are the features of atmospheric circulations on monsoon:

• Summer Monsoon (June–September): Land heats faster than the ocean, creating low pressure over India, pulling in moist southwest winds, causing heavy rainfall.
• Winter Monsoon (October–March): Cooling landforms high pressure, pushing dry northeast winds, leading to dry conditions.

Seasonal Wind Shifts and Rainfall Impact

• Jet streams influence monsoon strength and variability.
• El Niño weakens monsoons, while La Niña strengthens them.
• Anomalies in monsoonal circulation impact Indian agriculture, floods, and droughts.