Coriolis term:

The Coriolis force arises from the fact that we have a coordinate system that is relative to a location on the earth, while in fact, the earth is spinning. The symbol represents how fast the earth is spinning in space. The angular speed of rotation on any point on the earth also depends on latitude, . The symbol f, also known as the inertial frequency, is often used to represent the Coriolis force, so this term can also be written as f x v.

View an Animation of the Coriolis force.

This term is retained in the horizontal momentum equations but can be neglected as being small in the vertical (w) equation.