Week 6: World Climatic Systems & Winds

Understanding the World’s Climatic Systems & Winds

From the gentle breeze that cools a summer evening to the devastating force of a hurricane, wind is one of the most powerful forces shaping our planet.

Our atmosphere is a dynamic system that continuously redistributes heat and moisture across the planet. This movement influences global climates, weather patterns, and even ocean currents. In this blog, we will systematically explore:

✅ Why does wind exist?

✅ How do planetary winds shape the climate?

✅ What role do jet streams play in global weather?

✅ How do local winds like Chinook, Foehn, and Loo affect specific regions?

✅ What are cyclones, and how do they differ between the tropics and mid-latitudes?

✅ How do El Niño, La Niña, and the Indian Ocean Dipole (IOD) disrupt global weather?

Let’s begin our journey through Earth’s climatic systems and winds by first understanding the driving force behind them: pressure differences and the movement of air. 🌍💨

1. Why Does Wind Exist? 🌎💨

Wind is simply the movement of air caused by differences in atmospheric pressure. But what creates these pressure differences?

Fundamental Causes of Wind

1. Unequal Heating of the Earth 🌞
• The equator receives more solar radiation than the poles, leading to warmer air at the equator and cooler air at the poles.
• Warm air rises at the equator (low pressure), while cold air sinks at the poles (high pressure).
• This creates a pressure gradient, setting air into motion.
2. Pressure Gradient Force (PGF) 📉📈
• Air always moves from high-pressure areas to low-pressure areas to balance the differences.
3. The greater the pressure difference, the stronger the wind.
   
   
   
   
   
4. Coriolis Effect 🌍
• Due to Earth’s rotation, winds are deflected:
• To the right in the Northern Hemisphere.
• To the left in the Southern Hemisphere.
  
  
  
5. Frictional Force 🌲🏙️
• Near the Earth's surface, natural and man-made structures (mountains, forests, buildings) slow down winds, influencing local wind patterns.

Fig No. 1 - Movement of air from high to low pressure due to Coriolis Effect.

2. Planetary Wind Systems: The Engine of Global Circulation

Since the Earth is heated unevenly, large-scale wind patterns emerge to redistribute heat and moisture. These patterns are part of the global atmospheric circulation system.

The Three-Cell Model of Atmospheric Circulation

The Earth’s atmosphere is divided into three major convection cells in each hemisphere, known as the:

1. Hadley Cell (0°–30° latitude) 🌞🌧️
• Rising warm air at the equator forms the Intertropical Convergence Zone (ITCZ), causing heavy rainfall and tropical climates.
• Air descends at 30° latitude, forming deserts like the Sahara, Atacama, and Kalahari.
• Trade winds (Easterlies) move toward the equator from the subtropical high-pressure zones.
2. Ferrel Cell (30°–60° latitude) 🌦️🌬️
• Acts as a transition between the Hadley and Polar cells.
• Westerlies dominate, moving air from west to east, affecting temperate weather patterns.
• Responsible for storm systems and cyclones in mid-latitudes.
3. Polar Cell (60°–90° latitude) ❄️
• Cold air sinks at the poles, forming polar high-pressure areas.
• Air moves toward 60° latitude, forming the polar easterlies.

Fig No. 2 - Three-cell Model of Atmospheric Circulation

3. Jet Streams: The Fast Lanes of the Atmosphere ✈️🌪️

Jet streams are narrow bands of fast-moving winds located in the upper troposphere (9-16 km altitude). These winds can reach speeds of 160-300 km/h and significantly influence weather and climate.

Types of Jet Streams

1. Polar Jet Stream (PJ) 🌨️
• Found at 60° latitude.
• Strongest in winter, guiding temperate cyclones and influencing North America, Europe, and Asia.
2. Subtropical Jet Stream (STJ) 🌞
• Found at 30° latitude.
• Affects tropical weather systems and plays a role in Indian monsoons.
3. Tropical Easterly Jet Stream (TEJ) 🌊
• Influences monsoon rainfall in South Asia.

Fig No. 3 - Jet Streams as per the Three-cell Model

Fig No. 4 - Jet Streams

Fig No. 5 - jet streams section on the atmosphere of Northern Hemisphere

4. Local Winds: Small-Scale Wind Systems with Big Impacts

Local winds develop due to temperature differences over small regions and influence climate, agriculture, and daily life.

Famous Local Winds

1. Chinook (USA & Canada) 🌄
• Warm, dry winds that melt snow rapidly in the Rocky Mountains.
• Known as "snow eaters".
2. Foehn (Europe) ⛰️
• Similar to Chinook, warming valleys in the Alps, aiding agriculture.
3. Loo (India & Pakistan) 🔥
• A hot, dry summer wind, known for causing heat strokes.

Fig No. 6 - Foehn wind path

Fig No. 7 - Chinook wind path

Fig No. 8 - Local winds of India

5. Cyclones: Tropical vs. Temperate 🌪️

Cyclones are low-pressure systems with rotating winds.

Tropical Cyclones (Hurricanes, Typhoons, Cyclones) 🌀

• Form over warm ocean waters (>26°C).
• Regions: Atlantic (Hurricanes), Pacific (Typhoons), Indian Ocean (Cyclones).
• Structure:
• Eye: Calm center.
• Eyewall: Intense storms.
• Spiral Rain Bands: Heavy rainfall.

Temperate Cyclones (Mid-Latitude Storms) 🌦️

• Form at mid-latitudes (30°-60°) due to air mass collisions.
• Steered by the Polar Jet Stream.
• Cause winter storms and heavy rainfall.

Fig No. 9 - Tropical cyclone

Fig No. 9 - Temperate cyclone

6. Ocean-Atmosphere Interactions: El Niño, La Niña & IOD 🌊

El Niño (Warm Phase) 🔥🌊

• Unusual warming of the Pacific Ocean.
• Causes droughts in India & Australia, floods in South America.

La Niña (Cool Phase) ❄️🌊

• Opposite of El Niño – cooling of the Pacific.
• Leads to stronger monsoons and hurricanes.

Indian Ocean Dipole (IOD) 🌏

• Positive IOD: Warmer Indian Ocean → Stronger Indian monsoon.
• Negative IOD: Cooler Indian Ocean → Weaker monsoon.

Fig No. 10 - El Nino conditions

Fig No. 11 - La Nina conditions

Fig No. 12 - ENSO

Fig No. 13 - Indian Ocean Dipole - positive phase

Fig No. 14 - Indian Ocean Dipole - Neutral phase

Fig No. 15 - Indian Ocean Dipole - negative phase

Practice Questions

🔹 Multiple Choice Questions (MCQs)

1. What is the primary cause of wind movement?

a) Rotation of the Earth.

b) Difference in atmospheric pressure

c) Gravity

d) Magnetic field

2. The Coriolis effect deflects winds in which direction in the Northern Hemisphere?

a) Left

b) Right

c) Upward

d) Downward

3. Which wind belt is responsible for the world’s major deserts?

a) Trade winds

b) Westerlies

c) Polar easterlies

d) Subtropical high-pressure belt winds

4. Jet Streams are found at which level of the atmosphere?

a) Troposphere

b) Stratosphere

c) Mesosphere

d) Thermosphere

5. El Niño is characterized by:

a) Cooling of the eastern Pacific Ocean

b) Weakening of trade winds

c) Increased rainfall in India

d) Strong upwelling along the South American coast

 

🔹 Fill in the Blanks

1. Winds blow from ______ pressure areas to ______ pressure areas.
2. The three types of atmospheric circulation cells are ______, ______, and ______.
3. The Intertropical Convergence Zone (ITCZ) is associated with ______ winds and heavy rainfall.
4. The most intense part of a tropical cyclone is the ______.
5. The warm phase of the Indian Ocean Dipole (IOD) is called ______ IOD.

 

🔹 One-Word Answers

1. What is the instrument used to measure wind speed?
2. What type of wind is the Loo?
3. Name the fastest winds found in the upper atmosphere.
4. Which wind belt influences temperate cyclones?
5. What is the calm region around the equator called?

 

🔹 One-Sentence Answers

1. What is the Coriolis effect?
2. Why don’t cyclones form at the equator?
3. What is the role of the Subtropical Jet Stream in monsoons?
4. How does La Niña impact India?
5. Why are deserts found at 30° latitude?

 

🔹 Short Answer Questions (2-3 sentences)

1. Differentiate between planetary winds and local winds.
2. Explain the formation of a tropical cyclone.
3. What is the role of the Indian Ocean Dipole (IOD) in monsoons?
4. What are the impacts of El Niño on different parts of the world?
5. How do Westerlies influence weather in temperate regions?

 

🔹 True or False

1. The Hadley Cell is responsible for trade winds.
2. The jet streams always flow from east to west.
3. La Niña weakens the Indian monsoon.
4. The Loo is a cold wind.
5. The Subtropical High-Pressure Belt is associated with deserts.

 

🔹 Match the Following

Column A	Column B
Hadley Cell	Trade Winds
Ferrel Cell	Westerlies
Polar Cell	Polar Easterlies
Jet Streams	Upper Atmosphere
El Niño	Warms Pacific Ocean

 

🔹 Diagram-Based Questions

1. Label a world map with the major wind belts (Trade Winds, Westerlies, Polar Easterlies).
2. Draw and label a cross-section of a tropical cyclone.
3. Illustrate the effects of El Niño on global weather patterns.

 

🔹 Analytical Questions

1. Why is the Coriolis effect stronger at the poles and absent at the equator?
2. How do Jet Streams affect commercial aviation?
3. Compare and contrast El Niño and La Niña in terms of oceanic and atmospheric conditions.
4. Explain why cyclones weaken after making landfall.
5. Discuss the role of the Polar Jet Stream in the formation of temperate cyclones.

 

🔹 Case Study-Based Questions

1. Case Study: The 2015 El Niño Event
• The 2015-16 El Niño was one of the strongest ever recorded, causing severe droughts in India, Australia, and Africa, and catastrophic floods in South America.
  Q1: Explain the global effects of El Niño, particularly its impact on monsoons in India.
2. Case Study: The Great Chinook of 1962
• A historic Chinook wind event in 1962 saw temperatures in Montana, USA, rise from -48°C to 9°C within 24 hours, melting snow rapidly.
  Q2: How do Chinook winds affect agriculture in North America?
3. Case Study: The Role of Jet Streams in Aviation
• Commercial airlines use jet streams to shorten flight durations and reduce fuel consumption. A 2020 flight from New York to London took just 4 hours 56 minutes due to a strong jet stream.
  Q3: Why do pilots prefer flying in jet streams from west to east?

 

🔹 Higher-Order Thinking Questions

Cyclones & Atmospheric Circulation

1. Why do hurricanes never form near the equator, despite warm ocean temperatures?
2. Why do westerlies dominate mid-latitude regions, and how do they affect weather in North America and Europe?
3. If the Earth's rotation slowed down, how would global wind systems be affected?

Ocean-Atmosphere Interactions: El Niño, La Niña, and IOD

4. Compare the effects of La Niña and El Niño on the global climate.
5. How does the Indian Ocean Dipole (IOD) influence the monsoons in India?

 

🔹 Comparative Questions

Feature	El Niño	La Niña	Indian Ocean Dipole (IOD)
Temperature Effect	Warmer Eastern Pacific	Cooler Eastern Pacific	Warmer/Colder Indian Ocean
Trade Winds	Weakened	Strengthened	Normal/Disrupted
Impact on India	Weaker monsoon, drought	Stronger monsoon, floods	Increased/Decreased rainfall

Q: Identify the weather phenomenon that causes severe droughts in India and heavy rainfall in South America.

 

🔹 True/False Questions with Explanations

1. Tropical cyclones weaken after landfall because they lose their heat source.
2. Temperate cyclones form due to warm ocean waters.
3. Jet Streams move from east to west in both hemispheres.
4. The Loo is a cold wind.
5. The trade winds are westerly winds.

 

🔹 Diagram-Based Questions

1. Draw and label a Hadley Cell, Ferrel Cell, and Polar Cell.
2. Illustrate the structure of a tropical cyclone.
3. Show the effects of El Niño on global climate.

 

🔹 Real-World Application Questions

Cyclones & Jet Streams

1. How do forecasters use Jet Streams to predict the path of a cyclone?
2. How did the 2020 Super Cyclone Amphan intensify so quickly in the Bay of Bengal?

El Niño & La Niña in Agriculture

3. Why did coffee production in Brazil decline sharply in 1997-98?
4. How does La Niña affect fishing in Peru?

 

🔹 Challenge Questions (For Deep Thinking)

1. If the Earth's axial tilt changed, how would planetary winds be affected?
2. How would a significant slowdown of ocean currents impact global wind circulation?
3. Why do the strongest cyclones form in the Bay of Bengal and not the Arabian Sea?