The Coriolis effect - optical illusion or real force?

The Coriolis Effect is a purely "optical illusion" when a constant rectilinear motion appears to be curved when viewed from a rotating system. But how can an "optical illusion" have a profound physical effect on the atmospheric motions?

 

It has to be remembered that motions on a rotating planet are also affected by the planet's gravitational attraction.

 

This real force not only prevents the moving body from escaping from the planet, but also it is involved in the deflection mechanism.

 

It will be suggested that we are dealing with two Coriolis Effects: one which can be regarded as a "optical illusion" and another which cannot be regarded as a purely "fictitious" force.