20.12 Wind

20.12.2 Describe the effect of the Coriolis force on moving air.

The Coriolis force is an apparent force caused by the rotation of the Earth.

It causes moving air to be deflected:

• to the left in the Southern Hemisphere
• to the right in the Northern Hemisphere

The Coriolis force does not start the wind. Air begins moving because of the pressure gradient force, from higher pressure toward lower pressure. Once the air is moving, the Coriolis force changes its direction.

The Coriolis effect:

• is zero at the equator
• becomes stronger toward the poles
• increases as wind speed increases

In the Southern Hemisphere, this leftward deflection contributes to winds flowing:

• clockwise around low-pressure systems
• anticlockwise around high-pressure systems

Key point

Southern Hemisphere = moving air is deflected to the left.

20.12.4 State the horizontal component of the Coriolis force equation.

The horizontal component of the Coriolis force is:

C = 2VΩ sin φ

Where:

• C = Coriolis acceleration
• V = speed of the moving air
• Ω (omega) = angular velocity of the Earth
• φ (phi) = latitude
• sin φ = accounts for the effect of latitude