Lee County, Florida
Southwest Florida Saltwater Tides in a printable yearly format
Pine Island -
Ft. Myers -
Understanding Tidal Movements
The tide is the vertical rise and fall of the sea level surface caused primarily
by the change in gravitational attraction of the moon, and to a lesser extent the
sun. As the earth spins on its axis the centrifugal force results in slightly deeper
water near the equator as opposed to shallower water at the poles. In fact it causes
a flow from the poles to the equator.
The earth is also in orbit around the sun (one
revolution in one year) creating not only another centrifugal force but also a gravitational
interaction. These two yield a bulge on the night site (centrifugal) and a bulge
on the day site (gravitational) both of them moving as the world turns. Therefore,
a certain place on this world will experience two high and two low tides each day.
With these forces alone, we would not have spring tides and neap tides. Spring tides
have higher high tides and lower low tides whereas neap tides have lower high tides
and higher low tides. Hence, the range (difference in water level between high and
low tide) is much larger in a spring tide than in a low tide.
These differences in range can be explained if we include the moon into our earth-sun
system. The moon and the earth orbit each other around a point (called the barycenter
or baricenter) 2000 odd kilometres inside the earth, creating a centrifugal and a
gravitational bulge. Moreover, despite the sun's immensely larger mass, the moon
exerts a 2.25 times larger gravitational attraction, since the moon is much closer
to our earth.
It is the combined effect of the sun and moon that creates spring and neap tides.
In the animation the gravitational forces of both the sun and the moon are taken
into account. When aligned with the earth they combine their attraction and otherwise
they counteract their attraction. The sun is located in the corner right below, far
outside this picture (note the eclipse) while the moon is revolving round the earth.
One full circle corresponds to one lunar cycle (about 28 days).
Click red stars or text below for a 3 page 2011 printable tide outlook
Click on a red star for a printable version in PDF for the entire 2012
Click on a red star for a printable version in PDF for the entire 2012
