Avgeek Alert: The Coriolis Effect & How It Affects Flights


Let’Here’s simple experiment: find a direct round-trip from Madrid to New York City and have a look at the duration of the outbound and the return. Under normal conditions, flying from Madrid to New York takes about eight and a half hours. From New York to Madrid, just over seven. How can this be, if in theory we’re traveling the same distance? Enter the Coriolis force, aka Coriolis effect.


What Exactly Is It?

Described in an 1835 paper by French scientist Gaspard-Gustave Coriolis, this effect created by the rotation of the Earth is a curious phenomenon indeed. Imagine a disk in constant rotation, always at the same speed. If we were to throw a ball from the center of the disk to a specific point on the end, its trajectory, which is straight, would visually describe a curve in the opposite direction towards which the disk is moving.

In other words, the Coriolis effect is the deviation of the trajectory of an object that moves in a straight line when it is inside another rotating object.

Well, the same thing happens on Earth. Our planet rotates on its own axis at a constant speed from west to east. If we threw a ball from the North Pole to the equator in a straight line, the ball would deflect to the right from the point where we threw it, due to the rotational motion. Consequently, winds in the northern hemisphere will always veer to the “right”.

In the southern hemisphere, exactly the opposite occurs: if we could throw that ball from the South Pole towards the equator, seen from the point of launch, the ball, moving while the Earth is moving, would describe a visually curved trajectory that would move towards the “left”. In order to see how the Coriolis effect works in real life, this video of an experiment with water is very revealing.


Does the Wind Blow the Same Everywhere? 

Here we’d have to get into meteorology, but the quick answer is no: wind does not move nor is it as strong on the earth’s surface as, for example, at the height at which airplanes usually fly.

At ground level, the wind blows more gently than at great heights, but its direction is more unpredictable: the terrain, the effects of friction and even issues such as buildings mean that its behavior is not always the same.

Way above, when we fly, the wind is stronger, but it always tends to blow in the same direction: from west to east. If we’re in the northern hemisphere, the wind will move mainly to the “right”. If we are in the south, to the “left”.


Does the Coriolis Effect Affect Every Point on the Globe in the Same Way?

The Coriolis effect is one of the main factors affecting atmospheric circulation patterns on Earth. Therefore, not only meteorologists take it very much into account, but also pilots.

When a pilots fly from point A to point B, they must know that if they change hemispheres, the direction of the wind will change as well. And that the Coriolis effect is greater the closer we get to the poles, and zero at the equator.

So then we have a northern hemisphere in which, up in the sky, the wind blows mainly to the right, from west to east. Let’s think about our example at the beginning of the article. The Madrid-New York route is from east to west, and the New York-Madrid route is from west to east. In other words, on the return flight, the usual thing is that the direction of the wind shortens the trajectory.

If we enter the Madrid-Buenos Aires route in our search engine, we’ll see that, although there is indeed a difference between the outbound and return flights, it is much less than in the first example. That’s because while flying in the southern hemisphere, the wind blows backwards, and after crossing the equator it blows in favour.


The Jet Streams

In the upper layers of the atmosphere, large air currents called jet streams are formed due to the difference in temperature between different air masses (it’s considered a jet stream as of a speed of 60 knots or 112 km/70 mph). With such an air current in its favor, an airplane will arrive at its destination more quickly (and vice versa).


A Very Visual Example of the Coriolis Effect

Surely this unusual effect has been explained to you more than once using water. Plug the sink and fill it about a third of the way up. Remove the stopper and note the direction of the swirl of water as it drains. If you live in the northern hemisphere, it will move to the right, or clockwise; if in the south, to the left.


Photo | JJFarquitectos