The rotation of the Earth deflects circulating air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

Background

If the Earth did not rotate and remained stationary, the atmosphere would circulate between the poles and the equator in a simple back-and-forth pattern.
Because the Earth rotates, circulating air is deflected toward the right in the Northern Hemisphere and toward the left in the Southern Hemisphere, resulting in curved paths.
This deflection is called the Coriolis effect.
It is named after the French mathematician Gaspard Gustave de Coriolis, who studied the transfer of energy in rotating systems like waterwheels.
Coastal currents are affected by local winds. Surface ocean currents, which occur on the open ocean, are driven by a complex global wind system.
To understand the effects of winds on ocean currents, one needs the Coriolis force and the Ekman spiral together.