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

Although some readers may be familiar with this meteorological phenomenon, others may never have heard of the Coriolis Effect. We take a close look at this occurrence, what it is, and how it works.

The Coriolis Effect describes the force generated by the Earth's eastward rotation, which results in air movement being deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. It is one of the primary driving forces of global wind patterns and weather events.

The Coriolis Effect is so important, in fact, that it influences almost every significant weather event occurring around the world. And it all directly results from the Earth's rotation:

The Coriolis Effect is caused by the Earth's rotation from west to east. This causes a deflection in air movement as it travels away from Polar & Equatorial regions, respectively. 

This phenomenon is responsible for the formation of some of the world's largest weather systems like hurricanes, typhoons, and tropical storms, as well as repeating circulating air masses like Trade Winds.

The principle may sound simplistic, but understanding it is a bit more complex. If one simply tries to put it into words, it won't make sense. For this reason, we will use an analogy alongside 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 weather systems and events, wherever it is formed on the planet.

How Exactly Does The Coriolis Effect Works

To best understand the earth's rotation, and the resulting influences 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 two polar regions, while the green figure the tropical regions.

Now let's flip the map sideways as 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.

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 the 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?

The illustrations above will give you a clear example of how just one 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 strengthens 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 develop hurricanes & typhoons in this article.)

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) have 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 in 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 persistent 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.

Conclusion

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.

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Until next time, keep your eye on the weather!