Because of its rotation the Earth was formed in a slightly flattend shape. This shape is such that the gravitational force at any point of the Earth surface is slightly tilted away from the equator as displayed in the figure below.

Gravitational force off-set towards the pole from the local vertical Decomposition of the gravitational force in a vertical and a horisontal component "Centrifugal force" orthogonal to the polar axis Decomposition of the "centrifugal force" in a vertical and a horisontal component The Earth has an oblate shape such that the horisontal component of the gravitational force prevents a mass point at rest on the surface to slide away towards the equator

The force component in the local equatorial plane caused by this tilt has exactly the strength required to prevent that the Earth rotation makes a "mass element" to slip away towards the equator.

As long as the atmosphere is at rest relative to the Earth surface underneath the equatorial component of the gravitational force has the same strength as the equatorial component of the "centrifugal force" and the atmosphere is at an "equilibrium state" relative to the rotating Earth. But if the atmosphere is put in motion, i.e. if there is wind, the balance between the gravitational force is disturbed and an north/south oscillation around the equilibrium will result. Because of the different rotational velocities of the Earth surface at different latitudes this oscillation will take the form of "whirls" relative to the Earth surface!

A solution to the equation of motion (with the "coriolis term" included!) for a mass point sliding on the Earth surface is displayed in the next figure!

Latitude 50.0 deg North velocity 50 m/s towards East Latitude 45.7 deg North, Longitude + 5.8 deg , velocity 50 m/s towards South Latitude 41.4 deg North, Longitude - 0.7 deg , velocity 50 m/s towards West Latitude 45.7 deg North, Longitude - 7.3 deg , velocity 50 m/s towards North Latitude 50.0 deg North, Longitude - 1.5 deg , velocity 50 m/s towards East A solution to the equation of motion for a mass point sliding on the Earth surface

Initially the mass point is moving with a velocity of 50 m/s over the Earth surface, this is the red point. As its eastward velocity is higher then that of the Earth surface the gravitational component tangential to the Earth surface is here too weak to prevent the mass point from starting to slide southward towards the equator. At its path towards south the local velocity of the Earth surface gets higher and at the green point the eastward velocity of the mass point is the same as that of the local Earth surface. But here the mass point has picked up speed towards south and this southward movement continues and only comes to a halt at the blue point. At this point the Earth surface moves 50 m/s faster towards east then the mass point. As now the tangential component of the gravitation is higher then what is needed to prevent the mass point from sliding towards the equator the mass point is instead accelerated towards north until it has reached the yellow point. But at this time the mass has picked up enough speed to continue further north to the black point and everything starts over again from the beginning.