The Coriolis effect
Originates because earth spins on its rotational axis
Angular rate of movement to E is constant along a longitude line, but absolute rate of movement to E depends upon latitude
At the equator, absolute rate is 1670 km/hr
At 30° N (or S), it is 1446 km/hr
As a mass of air or water moves from the equator to 30°N or S, inertia of the mass of water or air causes the mass to appear (from a vantage point away from earth) to veer to the right in the northern hemisphere or to veer to the left in the southern hemisphere