What causes tides? Tides are the periodic rise and fall of the water within oceans, seas, bays and other major water bodies, caused by the combined gravitational influences of the sun and moon and their positions relative to the Earth. Complex gravitational and centrifugal forces are applied to the earth’s oceans by the sun, moon and the earth’s rotation. Peaks in tidal movement depend on the rotation of the earth and the moon’s orbital location, which has a greater effect on the tides than the sun. The moon moves around the earth in an elliptical orbit, taking about 29 days to complete one cycle (a lunar month). The overall gravitational force is greatest when the moon is closest to the earth (perigee), and least when it is furthest from the earth (apogee).
Predicting tides. The National Oceanic and Atmospheric Association (NOAA) has been measuring tides around the country since the early 1880s. Modern tidal recording instruments include advanced acoustics and electronics. Tidal predictions are based on these tidal measurements in many areas over an extended period of time. Predictions then go into tide tables that show times and heights of the highest and lowest tides.
What are spring tides? The term “spring tide” is the term used to define the highest tide in each lunar month. A spring tide occurs every 14.5 days, when the earth, moon and sun all align in what is termed syzygy. The spring tidal range varies from month to month.
For more information, email Candice Allouch (email: firstname.lastname@example.org) at FIU’s Sea Level Solution Center.