As the Earth spins west to east a phenomenon known as Coriolis creates a generalised movement of currents and winds. If Earth was a perfect sphere covered by a uniform layer of water, this would manifest into currents and winds moving east to west and a series of interlocking eddies north and south of the equator, of diminishing size from the equator to the poles (like in the diagram below).
Anders Persson, Wikimedia Commons. A generalised image of coriolis wind patterns..
These are the patterns that drive global weather systems but are more complex and interrupted by land masses and influenced by seasonal climatic changes (monsoons) and periodic variations (La Niña and El Niño).
The pattern of these eddies are mirrored in terms rotation direction and properties north and south of the equator.
