1. What are tides?
Tides are the rising and falling of the water level in the ocean. Tides are caused by the gravitational attraction of the moon and the sun. The moon has the single greatest influence on the tides. Tidal forces cause the water level to rise and fall in a cyclic manner. To make the water level rise and fall, a lot of water gets moved around and this can cause tidal currents.
Tides in Narragansett Bay are semidiurnal, meaning that there are two high tides each day and two low tides each day.
The tidal range changes depending on the relative positions of the moon and the sun. If the moon and the sun are acting together, we get a higher than normal tide called a spring tide. When the moon and sun are acting opposite to each other, we get a lower than normal tide called a neap tide. There are other astronomical factors that can change the tidal height.
For an in-depth explanation of how the gravity of the moon and the sun cause tides, see this web site:
http://www.co-ops.nos.noaa.gov/about2.html
In addition, there are local influences on the tides. Some of those factors are:
- Shape of the land
- Shape of the ocean floor (bathymetery)
- Depth of water
- Restrictions to flow (narrow inlets to bays, etc.)
- Local winds
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