Due to the influence of geostrophic force, objects moving horizontally on the earth deflect to the right in the northern hemisphere and to the left in the southern hemisphere, instead of to the equator. Therefore, in the northern hemisphere, the southern hemisphere and the equator, the bath water rotates in different directions.

There is no vortex at the equator. The vortex in the northern hemisphere rotates counterclockwise and the vortex in the southern hemisphere rotates clockwise.

Every point on the earth moves in a circle around its axis, and the earth is abstracted into a sphere, which rotates at a constant speed around a straight line passing through the center of the sphere. Every point on the sphere moves in a uniform circle around the earth axis. The radius of motion is the vertical line of the earth axis from this point, and the distance from the intersection of the vertical line and the earth axis to this point is the radius of motion.

Extended data:

The so-called phenomenon of going north, south and north is due to the Coriolis force generated by the earth's rotation.

1835, coriolis pointed out in the article "relative motion equation of object system" that if an object moves relatively in a reference frame rotating at a constant speed, there will be an inertial force acting on the object which is different from the usual centrifugal force, and this force is called compound centrifugal force. Later generations named the compound centrifugal force "Coriolis force" after him.

Coriolis force is generally only considered in large-scale fluid flow, while typhoons, ocean currents and other small-scale ones are only the result of local turbulence and belong to uncertain factors. This is related to the direction of running water, the size and shape of holes. So the small water vortex on the equator may be counterclockwise or clockwise.

Baidu Encyclopedia-Earth Rotation Deviation