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Analyzing the large-scale wind systems that move across the planet and why they curve.
If you fired a giant cannonball from the North Pole directly at the Equator, why would it land hundreds of miles to the west of its target even if there was no wind?
Imagine you are standing on a spinning merry-go-round and try to throw a ball to a friend on the other side. The ball appears to curve! This happens on Earth because our planet is a sphere rotating on its axis. This phenomenon is called the Coriolis effect. Because the Earth rotates faster at the Equator than at the poles, moving air is deflected. In the Northern Hemisphere, winds always curve to the right of their path. In the Southern Hemisphere, they curve to the left. This 'invisible force' is what prevents wind from simply blowing in straight lines from the poles to the Equator.
Quick Check
If an airplane is flying from the Equator toward the North Pole, which direction will the Coriolis effect pull it?
Answer
To the right (East).
Earth's surface is divided into three main 'cells' of moving air in each hemisphere. First, the Trade Winds blow from latitude toward the Equator (). They are steady and strong, used by early merchants to sail across oceans. Second, the Prevailing Westerlies blow from to latitude. These winds move from West to East and are responsible for most of the weather patterns in the United States and Europe. Finally, the Polar Easterlies blow cold air from the poles () down to latitude, moving from East to West.
To find which wind belt you live in, follow these steps: 1. Identify your latitude (e.g., Chicago is at approximately N). 2. Check the ranges: (Trade), (Westerlies), (Easterlies). 3. Since falls between and , Chicago is in the Prevailing Westerlies zone.
Quick Check
Which wind belt is located between and latitude?
Answer
The Polar Easterlies.
Not all parts of the ocean have strong winds. At the Equator, air is heated so intensely that it rises straight up, creating an area of very little horizontal wind called the Doldrums. Sailors could be stranded here for weeks. Similarly, at North and South, cool air sinks vertically toward the surface. This creates the Horse Latitudes. Legend says Spanish sailors stuck in these windless waters had to throw their horses overboard to save drinking water for the crew. These areas are characterized by high pressure and calm, dry air.
Imagine you are a captain in the year 1700 sailing from England ( N) to the Caribbean ( N). 1. You start in the Westerlies, which push you East, but you need to go South-West. 2. You must navigate through the Horse Latitudes at N, where you risk your ship stopping completely due to lack of wind. 3. Once past N, you catch the Trade Winds, which reliably carry you West toward your destination.
A weather balloon is released at S latitude and begins to travel North toward the Equator. 1. At S, it is in the Westerlies zone. 2. As it moves North toward S, the Coriolis effect pulls it to the left of its path of motion. 3. Because it is traveling North (up), a 'left' pull means it will drift toward the West.
What is the primary cause of the Coriolis effect?
Which wind belt moves weather across the United States from the West toward the East?
The Doldrums are located at the Horse Latitudes ( latitude).
Review Tomorrow
In 24 hours, try to sketch a circle representing Earth and draw the direction of the three wind belts from memory.
Practice Activity
Look up the latitude of three different world cities. Based on their latitude, determine which global wind belt they are located in.