2. Coriolis effect and surface circulation patterns

2.1. Coriolis effect

Coriolis Effect is the phenomenon where current and wind are deflected as they travel across or above the earth’s surface.
– In the North hemisphere the deflection is to the right → spin counterclockwise
– In the South hemisphere the deflected is to the left → spin clockwise

Coriolis effect is the single most important effect in physical oceanography. Coriolis force is a fictitious force that exists in all rotating reference systems. Newton’s second law in a rotational reference system is:

Coriolis force - Newtons' inertia law on rotating reference systems. Coriolis Centrifugal forces

Due to the slow rotation of Earth (T=24 h, ω=7,27×10-5 rad/s), the Coriolis force is very small. The effect of Coriolis is noticeable in large-scale and long-duration phenomena such as large-scale flow of wind and ocean currents. Such motions are constrained by the surface of the earth, so only the horizontal component of the Coriolis force is important.

A more intuitive explanation of the Coriolis effect: An object that is decoupled form the solid earth (such as ocean water and air) move in deflected track due to the fact that the Earth’s speed of rotation is slower at the poles that at the equator. Coriolis effect affects air and water masses and governs atmospheric and ocean-surface circulation patterns.

Coriolis Effect, North hemisphere deflection is to the right → spin counterclockwise

Simplified/intuitive explanation: The video below explains the Coriolis effect. If you have found a simpler explanation place let us know on the comments below

– Coriolis force is perpendicular to the velocity vector.
– The small scale, such as a sink at your house, other factors, such as the shape of the sink and the direction of initial velocity of the water are the important factors for the direction of spinning. Coriolis effect is way down to the list of phenomena that affect that flow.

f-plane is a Cartesian coordinate system on which the Coriolis force is assumed constant.

β-plane the Coriolis force is assumed to vary linearly with the latitute.

Further Reading

2.2. Inertial Oscillations

Inertial Oscillations (inertial wave): Is the motion of ocean water where only the Coriolis force acts on the water. Such a motion can be initiated when:

  • Wind blows across the sea for a short time
  • Water is exiting from the mouth of an estuary

After the initiation of the motion, only the Coriolis force acts on the water (no compensating hydrostatic pressure gradient as in geostrophic flow) and the water body is not in equilibrium.

In general, inertial oscillations are possible only when a fluid is rotating and the oscillation is in the bulk of the fluid, not at its surface. From the equations, it can be seen that the oscillation period is determined by the latitude.

T=2πf where f=2Ωsin⁡φ

Latidute [deg]Period [hours]
φ = 0T = infinite
φ = 10T =69 h
φ = 35T =21 h
φ = 45T =17 h
φ = 60T = 14 h
φ = 90T = 12 h

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