Question

the coriolis effect happens when ?

Answer 1

http://www.universetoday.com/73828/what-is-the-coriolis-effect/

Answer 2

The effect of the Coriolis force is an apparent deflection of the path of an object that moves within a rotating coordinate system. The object does not actually deviate from its path, but it appears to do so because of the motion.

In other words, the Coriolis effect lies in the Earth’s rotation. The Earth rotates faster at the Equator than it does at the poles. This is because the Earth is wider at the Equator. A point on the Equator has farther to travel in a day. This apparent deflection is the Coriolis effect. The wind is like the ball. It appears to bend to the right in the Northern Hemisphere. In the Southern Hemisphere, winds appear to bend to the left.

http://education.nationalgeographic.com/education/encyclopedia/coriolis-effect/?ar_a=1