Coriolis Force: Definition of Effect Caused by Earth’s Rotation

Coriolis force is an apparent inertial or fictitious force that arises when an object or mass is in motion within a frame of reference that rotates with respect to the inertial frame.  The Coriolis force deflects an object or mass to the left side in a frame of reference with clockwise rotation. Similarly, this force deflects an object or mass to the right side in a frame of reference with anticlockwise rotation. This deflection of the object or mass due to Coriolis force is known as the “Coriolis effect”.

Who discovered the Coriolis Force?

While the Coriolis force was recognized by many scientists previously, it was only in the year 1835 that a French Scientist named Gustave-Gaspard Coriolis published a paper mathematically explaining the Coriolis Force. Thus, this force was named after him.

Is Coriolis Force a Real Force?

No, Coriolis force is not a real force. It is an imaginary force invented by scientists to explain the motion of an object vis-a-vis Newton’s laws of motion (along with other real forces).  The Coriolis Force is considered to act perpendicular to the direction of the motion leading to a deflection in the path of the object.

Coriolis Effect and Earth’s Rotation

In geography, Earth’s rotation is considered as the main cause of the Coriolis force. We all know that Earth rotates on its axis from west to east.  The rotating Earth itself becomes a frame of reference for the moving air mass. When an air mass near the Earth surface is set in motion as a result of the pressure gradient force, it experiences a deflection in its path due to Coriolis force.

• Northern Hemisphere: When observed from the North Pole, the Earth’s rotation appears counter-clockwise. Thus,  the air mass or object moving from high pressure to low pressure in the Northern Hemisphere of Earth appears to deflects towards the right. 
• Southern Hemisphere: When observed from the North Pole, the Earth’s rotation appears counter-clockwise. Thus, the air mass or object moving from high pressure to low pressure in the Southern Hemisphere of Earth appears to deflects towards the left.

Why is Coriolis Effect Maximum at Poles?

The twisting of the underlying Earth’s surface due to the planet’s rotation increases with increases in latitude. Thus, when an object is moving horizontally and freely at a greater latitude, it experiences more deflection. As the effect of Earth’s rotation is highest at the poles, accordingly, the Coriolis force is experienced maximum at the Poles.

Why is Coriolis Force Zero or absent at the Equator?

Understanding from the aspect of the sense of rotation, an object or mass does not experience any turn or curve at the equator with respect to Earth’s surface. An object or mass moves horizontally and freely at the equator remains unconstrained and does not experience any external horizontal force. At the equator, the object/mass moving in a straight path experiences zero or no Coriolis force.

Example of Coriolis Force

• The Coriolis force contributes towards the maintenance of the wind belts and upper air circulations, including jet streams.
• Coriolis effect is the main reason which answers the much-asked question, “why hurricanes and cyclones spin in the opposite direction”.

Coriolis Effect on Other Planets

Similar to Earth, some planets of our solar system also experience the Coriolis force. The strength and impact of the Coriolis Force on planets depend on the size of the planet, the speed of its rotation, and the composition of its atmosphere. For example, Venus and Earth are almost the same in size but the rotation of Venus is comparatively slower than Earth. This results in a weaker Coriolis force on Venus. Planets like Jupiter and Saturn, on the other hand, experience the impact of the Coriolis force on a much larger scale due to its giant size and rapid rotation speed.