• The Coriolis Effect: Which way do planes fly the fastest?

Do you know what the Coriolis effect is? It is the phenomenon that explains questions such as: Does the speed of aeroplanes vary depending on the direction in which it is travelling? Which way does an aeroplane go faster, east or west?

We could propose that the rotation of the Earth might favor flying one direction over the other. For example, a child releases a balloon and, as the Earth rotates and passes beneath the balloon, the balloon can travel from Madrid to NY without any difficulties… But not quite and today we’ll explain you the reason.

Due to inertia, as the balloon ascends it stays above the boy all the way up. But when we take the wind into account, everything changes. Due to the rotation of the Earth which generates the Coriolis Effect.

Globally, the wind mainly blows from West to East, and this effect is even more pronounced at altitude in the Jet Stream, speeding journeys towards the East. So, in general but not always, aircraft can travel more rapidly from West to East.


By Kes47, CC BY-SA 3.0, Wikimedia Commons

What is the Coriolis Effect?

In the Earth’s atmosphere, air does not always flow in the same way. In the lower layers, air is confronted with friction, constructions and orography, so predicting its behaviour is difficult.

In the upper layers, however, things change, as air particles flow from areas of high pressure to areas of low pressure.

Due to the rotation of the Earth, these particles are induced a force perpendicular and to the right of their original trajectory. For this reason, we say that in the northern hemisphere the wind tends to veer to the right and in the southern hemisphere to the left.

This force is what we know as the Coriolis effect, which is responsible for the movement made by air currents at high altitude.

So which way do planes fly the fastest?

In general, but not always, aircraft travel faster travelling from west to east. Indeed, on a scheduled flight from New York to Malaga, for example, flight time can be reduced by almost 20% compared to the opposite route, from 8.5 hours to 7 hours.

An experiment with the Coriolis Effect

You may have found the explanation of the Coriolis effect a bit confusing, but don’t worry. Here’s an experiment so you can check it out for yourself at home.

It’s as easy as putting the stopper on the sink and filling it with water. Once you have a reasonable amount of water, turn off the tap and open the stopper. You’ll see a swirl, won’t you? And which way does it swirl?

If you read us from the northern hemisphere, you will see that it turns to the right; if, on the other hand, you read us from the southern latitude, it will turn to the left. This is the Coriolis effect.

What are jet streams?

Another factor contributing to the difference in the duration of aircraft routes is jet streams.

Jet streams are large air currents that form in the upper atmosphere. Jetstreams have their origin in the temperature difference between different air masses.

To be considered a jet stream they must reach a minimum speed of 60 knots, about 112 km/h. That’s a lot, isn’t it? Well, you should know that, in Europe, there are times when they reach 120 knots, which is 230 km/h.

In the northern hemisphere, jet streams flow from west to east, and if you’ve been paying attention… Yes, it’s because of the Coriolis effect.

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