With reference to “Coriolis force”, which of the following statements is/are correct?

It increases with increase in wind velocity.

It is maximum at the poles and is absent at the equator.

Select the answer using the code given below:

Question

With reference to “Coriolis force”, which of the following statements is/are correct?

It increases with increase in wind velocity.
It is maximum at the poles and is absent at the equator.

Select the answer using the code given below:

Accepted Answer

Both 1 and 2 Quick Verdict: Both statements are correct. The magnitude of the Coriolis force is directly proportional to the horizontal velocity of the wind (Statement 1) and the sine of the latitude, making it maximum at the poles and zero at the equator (Statement 2). Thematic Discussion: The Mechanics of the Coriolis Force Factors Determining Air Motion: If we assume that the Earth does not rotate, the location, motion, and direction of the air are determined by three primary factors: Gravitational force: This keeps the air as close to the Earth’s surface as possible. This is why the density of atmosphere decreases with increasing altitude.  Pressure gradient force: The most fundamental factor that physically moves the air from areas of high pressure to areas of low pressure. Under the influence of this force, the winds broadly shuttle between equator and poles.  Frictional force: Surface friction (from mountains, trees, and buildings) drags on the lowest layers of the atmosphere, reducing wind speed and causing localized turbulence that distorts its path. The Addition of the Coriolis Force: Because the Earth rotates on its own axis, a fourth factor—the Coriolis force—plays a role. Along with frictional force, this deflective force changes the direction of air motion. It is named after G.G. Coriolis, who formally analyzed it in 1835. Ferrel’s Law: The precise manner of this deflection is governed by Ferrel's Law, which states: "If one stands with one’s back toward the direction from where the wind is coming, the wind is deflected to the right in the northern hemisphere and to the left in the southern hemisphere." Effect on Cyclones: Once the wind is deflected to the right in the Northern Hemisphere, a low-pressure center is created to the left of the wind motion, and a high-pressure center to the right. The wind then circulates around this low-pressure center in a counter-clockwise direction. (In the Southern Hemisphere, the leftward deflection causes clockwise circulation). Why Does This Happen? The Law of Conservation of Angular Momentum To understand why the wind deflects, we must look at the physical laws governing rotating bodies. The angular momentum of a rotating body is the product of its mass, its angular velocity, and the square of its radius. As per the Law of Conservation of Angular Momentum, unless an external force is applied to it, the angular momentum of any rotating body remains constant. Therefore, if the radius of a rotating body decreases, it must rotate faster (increase its angular velocity) to conserve its original momentum. Moving Poleward (Radius Decreases): An airmass located at the equator has the highest angular momentum. When it starts moving toward the poles, it comes closer to the Earth’s rotational axis, losing its radius. To conserve its originally acquired higher angular momentum, the airmass increases its angular velocity. However, the Earth’s rotational speed decreases from the equator to the poles, creating friction that retards the airmass's velocity. To overcome this friction and maintain greater angular velocity, the airmass gets deflected at a right angle to its originally intended direction (driven by the pressure gradient) and moves eastward. Moving Equatorward (Radius Increases): Conversely, an airmass at the poles has the lowest angular momentum. When moving equatorward, it moves away from the rotational axis, increasing its radius. To conserve its lower angular momentum, it decreases its angular velocity. However, as it moves to lower latitudes, the Earth's rotational speed beneath it is increasing. The Earth's surface essentially moves ahead of the airmass, causing the airmass to appear deflected westward (to the right, as per Ferrel's law).