Why does the coriolis effect work differently within the Northern and Southern hemispheres?

Question

I know that winds go counterclockwise in the Northern hemisphere and clockwise in the Southern hemisphere due to the Coriolis Effect but why does the Coriolis Effect go in different directions?

Answer 1

Imagine you are standing facing the equator. In the Northern Hemisphere, your left hand is towards the direction of spin (east, where the Sun rises). In the Southern Hemisphere, your fight hand points in the direction of spin when facing the equator. The fact that the relationship between down and direction of spin is different is the reason for the difference. I can't go into more detail without diagrams.

Answer 2

Excellent question. But permit me to answer it in the correct mathematical manner. When you study the "equations of motion" on a rotating earth you will find there to be four components of the coriolis force (or more properly acceleration since we use forces per unit mass). I will only given you two of these components. Due to the northward motion of the air there is an eastward component of the coriolis force given by 2 O v sin phi where O, Greek symbol is omega, is the angular rate of motion of the earth, v is the northward component of motion and phi is the latitude which you are considering. Due to the eastward motion of the air there is a northward component of the coriolis force given by -2O u sin phi, where u is the eastward component of motion and the other symbols remain the same. Since this component is negative it acts in the southward direction. The Coriolis forces involve only those components of the total motion measured relative to a rotating frame, which lie in a plane perpendicular to the axis of rotation (equatorial plane). They are directed to the right of these velocity components in an equatorial plane with magnitude = 2 Omega V where V is the part of the velocity which lies in an equatorial plane as I have shown above. Finally, because the Coriolis acceleration is always perpendicular to the velocity of the air it can never change the speed of a parcel of air, only its direction of motion. This is the reason it is sometimes referred to as as deflecting force. You can experience this if you have one of those rotating platforms on a school playground near you. If you stand on one side and a friend stands on the other and while the platform is rotating you try to toss a ball to your friend you will observe the Coriolis acceleration. The ball will curve to your right. Finally, to answer your question specifically. Because the sin phi term is positive in the northern hemisphere and negative in the southern hemisphere the Coriolis accelerations are in opposite directions in the two hemispheres. These Coriolis terms simply fall out in the mathematics when you work with the equations of motion, but can be explained by the rotation of a coordinate system on a sphere.