• The earth makes one complete rotation on its axis every 24 hours.
  • An object on the equator travels the circumference of the globe (approximately 40,000 km) each day.
  • Objects at the Poles simply rotate around a vertical axis but don’t move in space.
  • The distance traveled per day (and velocity of rotation) decreases with increasing latitude.
  • For example:
    • Columbus, Ohio, located at 40oN, travels at 1284 km/hr (~360 meters per second)
    • New Orleans, Louisiana located along the 30th parallel rotates at 1452 km/hr (~400 m/sec)
    • Seward, Alaska (60oN) pokes along at only 838 km/hr.
  • Every point on the earth’s surface must make one complete rotation of the planet each day.
  • Objects on the earth’s equator travel further (and faster) than objects at higher latitudes.
  • A site located along the equator travels at 1675 km/hr, whereas a site along latitude 40oN (or 40oS) has a velocity of 1284 km/hr.
  • It is this contrast in velocity that results in the Coriolis Effect.

The Coriolis Effect can be a difficult concept to grasp because although we recognize that the earth rotates, it is difficult to accept that most of the population of North America is hurtling along at over a thousand kilometers per hour.

It is much like traveling in a car. Although we are sitting still in a car that is moving at 100 km/hr (62 mph), we recognize that we too are traveling at the same speed. If we were foolish enough to try to exit the vehicle we would have the same velocity as the moving car (until we hit something that wasn’t moving, e.g. the ground).

So what has all this got to do with the Coriolis effect?

This contrast in velocity with latitude causes travel paths (of winds, ocean currents, missiles etc) to be deflected to the right of their course in the Northern hemisphere (and to the left in the Southern Hemisphere).

Here’s why:

Imagine yourself in Panama City, Florida, near 30oN and 1100 km directly south of Columbus, Ohio.

You fire a rocket directly north at Noon.

The rocket travels north at 1100 km/hr. However, it also has the eastward velocity of the launch site (the earth is rotating to the east at a velocity of 1452 km/hr).

The rocket would then arrive in Columbus at 1 p.m,  IF Columbus was rotating at the same velocity as Panama City.

However, Columbus moves eastward at only 1284 km per hour.

So the rocket moves eastward an additional 168 km and it will land east of Columbus (somewhere near the border with West Virginia).

An object with an eastward component of velocity at the equator overshoots a target at 40oN on a rotating earth. The path of the object is deflected to the right relative to objects on the earth’s surface.

To the citizens of Columbus it would appear that the rocket was deflected to the right of its course.

If they sought to retaliate by launching a similar missile toward Panama City they would find that they too would miss their target by 168 km.

As Panama City moves east more rapidy than Columbus, the rocket would land west of the city, again an apparent deflection to the right of its (southerly) course.

The deflection is the Coriolis effect.

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