The ocean tides are manifested by alternating vertical displacements of the sea surface coupled with periodic horizontal movements of the water called the tidal currents. The ocean tides are caused by the gravitational forces produced by the moon and the sun. More exactly, the origin of tides is related with the non-homogeneity of the lunar and solar gravitational fields over the extent of the globe.
This package of computer simulations offers some dynamic illustrations for the properties of tide-generating forces that arise on the earth due to the gravitational field of the moon (or of the sun). The applets are created with the help of Easy Java Simulations tool developed by Francisco Esquembre, professor of Murcia University, Spain.
A detailed theoretical background (with relevant math equations) for the phenomenon of ocean tides can be found in the paper A Dynamic Picture of the Oceanic Tides available in the pdf format (170 KB). You will need the Adobe Acrobat Reader program to read the manual or to print out the hard copy (20 pages).
The simulations show the tidal forces in the geocentric reference frame that rotates together with the earth making one revolution during a day. We assume for simplicity that the celestial body creating these forces (the moon or the sun) occurs in the equatorial plane of the earth. Its distance from the earth is certainly much greater than shown in the simulation. This means that its image on the screen shows correctly only the direction toward the source body.
The program shows also the stationary tidal wave generated by these forces in a simplified model of the earth covered everywhere by the water envelope of equal depth. The amplitude of this wave is exaggerated in the simulation in order to make visible the peculiarities of the phenomenon.
The gravitational force of the moon exerted on any body on the surface of the earth is much smaller than the gravitational force of the sun. However, the earth is much closer to the moon than to the sun. Therefore the non-homogeneity of the lunar gravitational field is considerably greater than that of the solar field. It occurs that the moon-induced tides are more than twice greater than the sun-induced tides.
The Oceanic Tides – Overview