What Is The Coriolis Effect And How Does It Affect Our Weather?

What Is The Coriolis Effect heading

When you think back, you may remember your Geography teacher mentioning the term, "Coriolis Effect", at some point during your school years a long time ago. I am pretty sure not many of us paid much attention to it or even really understood it and how important a role it plays in our everyday lives through its influence on our global weather and climate.  

The Coriolis Effect is so important in fact, that it has an influence on almost any significant weather system, no matter where it occurs around the world. But what exactly is the Coriolis Effect and why is it so important? 

The Coriolis Effect is caused by the earth's rotation from west to east. This causes a deflection and variation in speed of the air moving away from the polar regions and the equator. This phenomena is responsible for the formation of some of the world's biggest weather systems like hurricanes, typhoons and tropical storms, as well as repeating circulating air masses like Trade Winds. 

Sounds too simplistic and confusing? Well, it is much more complex to be honest. Simply put into words it doesn't make sense, I know. For this reason I will use an analogy alongside an the appropriate illustrations to explain the principle in practice.

We will then continue and illustrate how it applies to the earth's rotation and its influence on all weather systems, no matter where it is formed on the planet.   

How Exactly Does The Coriolis Effect Works

To best understand the earth's rotation and the resulting influence on global wind movements, the analogy of a playground merry-go-round will be used.


You can use the illustration above to better understand the process. The merry-go-round is viewed from the top to best explain how the Coriolis Effect works.

Imagine the merry-go-round is spinning counterclockwise at a rapid speed. On the platform, the person in green and blue would have both completed one full rotation as the merry-go-round completed one rotation.

But, (as all of us who have been on the merry-go-round will know), the green figure would have traveled much faster and covered a bigger distance than the blue figure sitting closer to the center of the merry-go-round, in the same period of time.

When viewed from the top, the earth works in exactly the same way. This means the blue figure will represent the the two polar regions, while the green figure the tropical regions.

Global Surface Speeds

Now let's flip the map sideways like we would normally view a map of the world (as illustrated in the image above). The same principle explained in the previous section still applies, but from this view, the Coriolis Effect can be much better explained and viewed.

It is important to note that the speed of rotation in the tropics (indicated in green) is much faster than the speed of rotation at the poles (indicated in blue). This is the main driving force of the Coriolis Effect.

Global Wind Movement

The illustration above shows you exactly how the moving air is affected once it starts deviating away from the tropics and polar regions respectively.

Atmospheric elements (like moist air and clouds) at the tropics will always move at the same speed as the planet's surface below. If it is pushed off course by any air movement and starts moving north or south, it starts drifting over an increasingly slower moving surface.

As a result, the clouds or moist air will move faster than the surface below it as it continues to drift further away from the center of the earth. (Indicated by the red arrows in the illustration above.)

A similar but opposite scenario occurs to atmospheric elements originating over the poles. Atmospheric elements (like moist air and clouds) at the polar regions will also always move at the same speed as the planet's surface below. In this case however, if it is pushed off course by any air movement and starts moving north or south, it starts drifting over an increasingly faster moving surface.

As a result, the clouds or moist air will move slower than the surface below it as it continues to drift further away to the north (at the Antarctic), and to south (at the North Pole). (Indicated by the blue arrows in the illustration above.)

So the question remains. How does the Coriolis Effect cause and influence global weather systems around the world?

Low Pressure System

The illustrations above will give you a clear example of how just on type of weather system is formed as a result of the Coriolis Effect.

We now know that air moving away from the equator moves faster than the earth's surface beneath it. At the same time air moving away from the poles moves slower than the earth's surface beneath it.

Now let's introduce a low-pressure system to the scenario. The air from both the equator and polar region will be pulled towards and start rotating around the low-pressure system (Air always flow from an area of high-pressure to an area of low-pressure)

In the Northern Hemisphere, as illustrated above, this forms a counterclockwise rotation of winds around the low-pressure system. Over a warm ocean, hot moist air feeds the low pressure system, which in turn strengthen the wind rotation around it.

And this is exactly how a tropical depression is formed, which can develop into a tropical storm, and even eventually form a hurricane if the weather system grows strong enough. (You can read in detail how exactly low-pressure systems and the surrounding winds form hurricanes & typhoons in this article.)

In the Southern Hemisphere, the winds accelerate and rotate to the left as it moves away from the equator. This is indicated with the red arrows in the second illustration above.

As a result, the exact same weather systems that forms in the Northern Hemisphere around a low-pressure system, can form in the Southern Hemisphere. It applies to all low-pressure weather formations, from a small tropical depression to a typhoon. With one big difference...

This big difference being the rotation of weather systems. The wind in these systems are always clockwise as a result of the Coriolis Effect. This means all low-pressure systems in the Southern Hemisphere rotate clockwise, unlike their counterparts in the Northern Hemisphere.

Effects Of The Coriolis Effect

In explaining what the Coriolis Effect is, some of the biggest weather systems caused by this global phenomena has already been highlighted. Hurricanes, tropical cyclones and typhoons (all basically the same thing) has already been mentioned, as well as how the Coriolis Effect assists in their creation.

It also has a similar, but opposite effect on high-pressure systems around the world. Winds rotate away from the center of a high-pressure system (as opposed to low-pressure systems). As a result, high-pressure weather systems rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Another very important result of the Coriolis Effect, is the creation of Trade Winds. As air is warmed at the tropics and starts moving in a northerly direction, it is deflected to the right as a result of the Coriolis Effect.

As the air cools down, it descends back to earth (at about 30 degrees north latitude). As the air descends, it moves back to the equator from the Northeast to the Southwest. These big consistently circular air masses are called Trade Winds.

A more indirect impact of the Coriolis Effect is the effect on the world's ocean currents. Ocean currents are mostly driven by global winds. As most of the earth's largest currents circulate around the high-pressure regions called gyres, the impact of the Coriolis Effect is very evident here too.


I honestly don't blame you if your head is spinning from reading through all the terms like "rotation, right, left, clockwise, counterclockwise and deviating" spread throughout this entire article.

If everything is a bit unclear, just read through the article a couple of times and use the accompanying illustrations to better understand exactly how the Coriolis Effect works. It gets easier and more understandable. Just give it time.

I hope this article managed to shed some light on this sometimes "mysterious", but very important part of our global weather and climate called the Coriolis Effect.

Feel free to leave me any comments, questions or suggestions, and I will get back to you as soon as possible.

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Until next time, keep your eye on the weather!



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