📖 Lesson 2: Air Masses and Wind Patterns

👩🏽‍🏫 Introduction

Welcome to the world of moving air—on a global scale! 🌍💨

The weather around us isn’t random—it’s often carried by giant air masses and shaped by wind patterns that stretch across continents. Knowing how air masses form and move helps us predict whether we’ll need an umbrella or sunglasses.

In this lesson, you’ll learn how air masses and global wind belts influence weather patterns around the world—and even right here in West Africa.

📘 Core Concepts

🔹 What Is an Air Mass?

An air mass is a large body of air with nearly the same temperature and humidity throughout. It forms over regions called source areas (like oceans or deserts).

🔹 Types of Air Masses

🔹 How Do Air Masses Move?

Air masses move because of pressure differences and are steered by global wind patterns. When they move into a new area, they can bring sudden changes in temperature, rain, or storms.

When two air masses meet, the boundary is called a front. Fronts often lead to rainfall or storms.

🔹 Global Wind Patterns

🌬️ The Earth’s rotation and uneven heating create global wind belts.

ITCZ (Intertropical Convergence Zone):

• Where trade winds from both hemispheres meet

• Causes heavy rainfall in tropical regions

🧠 Why It Matters

Understanding air masses and wind patterns helps us:

• ☁️ Predict the weather

• 💧 Know when it might rain

• 🌾 Plan farming or fishing seasons

• 🌪️ Prepare for storms and dry spells

🧪 Real-Life Example

🔁 The Harmattan vs. Moist Tropical Air
In West Africa, the dry, dusty harmattan (from the Sahara) can meet the moist tropical air from the Atlantic. This clash causes dramatic weather shifts, like dryness, cool air, or thunderstorms.

🧩 Sample Problem Walkthrough

🧠 Problem: A warm, humid air mass (mT) replaces a cold, dry one (cP). What type of weather might follow?

✅ Step-by-Step Solution:

1. mT = warm and humid

2. cP = cold and dry

3. Warm, moist air rises over cold → forms clouds → rainfall
   ✔️ Answer: The region may experience warmer, wetter weather with rain or storms.

✍🏽 Practice Exercises

1. Fill in the blanks
(a) An air mass forms over a ______ region.
(b) The ITCZ causes heavy ______ in tropical areas.

Answers:
(a) source
(b) rainfall

2. Match the Air Mass

Answers:
(i) → C, (ii) → B, (iii) → A

3. Short Answer
What happens when two different air masses meet?
Sample Answer: A front forms, which may lead to clouds, rain, or storms depending on the air types involved.

🌀 Recap

• Air masses are large regions of similar air that move and cause weather changes.

• Trade winds and westerlies push them around the globe.

• The ITCZ near the equator causes tropical rains.

• In West Africa, the harmattan and moist tropical winds are major influencers of seasonal weather.

💭 Reflection Prompt

Look outside. Is the weather hot and dry? Cool and rainy? What kind of air mass do you think is influencing your region today?