The Coriolis effect

The Coriolis effect is an inertial force that seems to deflect moving objects on or above the surface of a rotating body, like the Earth. It's crucial to understand that it's an apparent force; the object isn't actually being pushed sideways. Rather, the ground beneath the object is moving due to Earth's rotation, making the object's path appear curved relative to the surface.

Understanding Earth's rotation and its impact on movement

The Earth rotates eastward, and the speed of this rotation is greatest at the equator and decreases as you move towards the poles. This difference in rotational velocity is key.

• When air moves from the equator towards the North Pole, it retains the faster eastward velocity it had at the equator. However, the ground beneath it is rotating eastward more slowly, causing the air to appear to be deflected to the right.
• Similarly, air moving from the North Pole towards the equator retains the slower eastward velocity it had at the pole. As it moves southward, the ground beneath it is rotating eastward faster, also causing the air to appear to be deflected to the right. The opposite happens in the Southern Hemisphere, causing a leftward deflection.

The Coriolis effect's strength varies with latitude, being strongest at the poles and negligible at the equator. This is due to the differing speeds of Earth's rotation at various latitudes. Importantly, the effect is an apparent deflection, not a true force pushing the object.

How the Coriolis effect shapes global wind patterns

The Coriolis effect is a fundamental driver of global wind patterns. It, combined with pressure gradients, creates the major wind belts that circulate air around the planet. These include:

• Trade Winds: Air moving from high-pressure zones near the tropics towards the equator is deflected, creating steady winds.
• Westerlies: Air moving from high-pressure zones towards the polar regions is deflected, creating the winds that dominate mid-latitude weather.

The Coriolis effect is also essential for the rotation of large-scale weather systems. In low-pressure systems, air flows inward towards the center. The Coriolis effect deflects this inward-moving air, causing the system to rotate. In the Northern Hemisphere, storms rotate counterclockwise, and in the Southern Hemisphere, they rotate clockwise.

Hurricanes and the Coriolis effect

In the case of hurricanes (or cyclones, typhoons), the Coriolis effect is critical. As air rushes towards the low-pressure center of the storm, it is deflected. This deflection causes the air to rotate around the center. In the Northern Hemisphere, this rotation is counterclockwise, while in the Southern Hemisphere, it is clockwise. This is what gives hurricanes their characteristic spiral shape and rotational motion.

The Coriolis effect’s role beyond storms

Beyond storm systems, the Coriolis effect influences the movement of air masses. These are large bodies of air with similar temperature and humidity. The effect changes the path they take, which affects weather over large areas.

Additionally, the Coriolis effect impacts ocean currents, which move heat around the globe.

However, the Coriolis effect has little impact on very small weather events, like local thunderstorms or gusts of wind. Its effects are most noticeable over long distances and time.