Schematic, simplified representation of atmospheric inertial oscillation. The black globe represents a weather balloon being swept along with inertial wind. Inertial wind is the name for the wind pattern that can occur in the absence of a pressure gradient.

With friction very small, inertial wind is a form of frictionless motion over the surface of an oblate spheriod. The Earth is an oblate spheroid, because it is rotating.

The vertical circles are not meridians. One full cycle of the animation corresponds to 24 hours. When the air mass is moving nearer to the pole it is picking up speed. Furthest away from the poles the velocity is slowest. The velocity with respect to the Earth is close to constant, the direction with respect to the Earth is constantly changing to the right.