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

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

Publicado por Samuel Pérez el 14 April, 2025

Última actualización: 3 December, 2025

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.

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.

What’s the Deal with the Coriolis Effect? Unpacking the Physics.

In essence, the Coriolis effect stems from inertia – an object’s tendency to maintain its current state of motion – operating within this rotating system. Consider the Earth, rotating West to East, as a sphere, points situated on the equator move considerably faster (approximately 1670 kilometres per hour) than points located nearer the poles.

Now, picture an air mass travelling northwards from the equator. It carries the eastward inertial velocity it possessed at the equator. As it moves over regions where the Earth’s surface is rotating more slowly eastwards, this difference in velocity causes the air mass to appear deflected towards the East (which is to its right in the Northern Hemisphere) relative to the ground.

Conversely, an air mass moving southwards from higher latitudes towards the equator starts with less eastward inertial velocity than the ground beneath it at lower latitudes. Consequently, it appears to lag behind the surface rotation, resulting in an apparent deflection towards the West (again, to its right relative to its path in the Northern Hemisphere).

Real-World Impacts of the Coriolis Effect

Whilst the underlying physics of the Coriolis effect can seem intricate, examining its real-world manifestations offers valuable insight into its operation and influence on our environment. Let’s consider some key examples.

Winds and Weather Systems

The Coriolis effect is fundamental to meteorology. Air naturally seeks to move from areas of high pressure towards areas of low pressure. In the absence of Earth’s rotation, this movement would result in straight-line winds. However, the Coriolis effect introduces a consistent deflection:

In the Northern Hemisphere, moving air is deflected towards the right relative to its direction of travel. Consequently, air converging into a low-pressure centre circulates anti-clockwise (forming cyclones or depressions), whilst air diverging from a high-pressure centre circulates clockwise (forming anticyclones).
In the Southern Hemisphere, the deflection is towards the left. This results in the opposite rotational patterns: low-pressure systems rotate clockwise, and high-pressure systems rotate anti-clockwise.

This large-scale deflection is instrumental in shaping the Earth’s major wind patterns, including the trade winds and the mid-latitude westerlies.

Ocean Currents

Similarly, the vast surface currents of the oceans are significantly influenced by the Coriolis effect. This deflection contributes directly to the formation of the major ocean gyres – extensive, rotating current systems. These gyres play a crucial role in the global climate system by transporting heat across the planet.

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.

Coriolis effect and the sink drain

A widely circulated notion suggests that the direction water rotates when draining from sinks or toilets differs between the Northern and Southern Hemispheres, attributing this phenomenon to the Coriolis effect. Despite its prevalence, this idea is, in fact, a persistent myth.

Whilst the Coriolis effect is indeed a real phenomenon influencing large-scale atmospheric and oceanic movements, its force is entirely negligible on the small scale of household drains. Other factors exert a far more dominant influence at this level.

The actual direction of rotation observed in draining water typically depends on more immediate, practical considerations:

The specific shape and geometry of the basin or toilet bowl.
Residual water currents or slight movements present before draining commences.
The way in which the water initially entered the basin.
Minor imperfections or asymmetries within the drain outlet itself.

Detecting a genuine Coriolis influence on such a small volume of water would require extraordinarily precise laboratory conditions. This would involve a perfectly symmetrical vessel, water left completely undisturbed for many hours to settle all residual motion, and a perfectly formed, centrally located drain – conditions far removed from any typical domestic setting.

Why you should care about the Coriolis effect as a pilot

For pilots, particularly during their training, grasping the Coriolis effect extends beyond mere scientific curiosity; it constitutes crucial operational knowledge for several key reasons:

Meteorological Comprehension: An understanding of the Coriolis effect is essential for comprehending why pressure systems and winds behave in the manner they do. This knowledge is fundamental to effective flight planning and maintaining operational safety.
Large-Scale Navigation Principles: The effect underpins the principles involved in long-range navigation. It helps explain why great circle routes are flown and highlights the necessity for navigation systems to compensate for the Earth’s rotation over extended distances.
Enhanced Situational Awareness: Whilst modern avionics systems automatically compensate for such factors, appreciating the underlying physics of the Coriolis effect fosters a deeper situational awareness regarding the forces acting upon the aircraft in various phases of flight.
Core Professional Knowledge: Familiarity with the Coriolis effect and its implications is considered part of the foundational scientific knowledge required of any competent aviation professional.

Now you know a little more about physics

You’ve seen that the Coriolis Effect is much more than a simple scientific curiosity; it is the ‘invisible’ but fundamental element that shapes our climate, directs ocean currents and, of course, is indispensable in aviation. And now you understand it much better!

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