Tides

In north east brazil the tides and the observation of tide tables are essential to be at the right spot at the best time. Ceara is generally in the area of  semi-diurnal tides "even" (two high waters and two low waters each day).

The gravitational forces between sun - moon and earth are responsible for the existence and the differences in tides. Further more the so called bathymetrie means the shape of the shoreline and the underwater relief are other influencial factors.

During a cycly of 29,5 days - the time the world is rounding the sun we have different types of tides.

spring-tides The tides result of the moons’ gravitational force which attracts the water stronger or less depending on the position of the moon to the earth.
There is "high tide" when the moon is in a line to the earth and sun and there is "low tide" when the moon is in a 90° angle to the earth and sun.
Consequently the moment of the tide is depending on the position of the moon to the earth.
As the sun has also a light gravitational pull to the water and earth there is a bigger bulge when the moon is lined up with the earth and sun.
Then the moons’ and suns’ gravitational force is added neap-tides together and this is the so called "spring tide".

neap-tidesIt’s "neap tide" when the sun is at a 90° angle to the moon.
The tidal range (heights) can vary a lot from one region to another as it’s depending on latitude and underwater topography.
A tide cycle is created by the outgoing (ebb) and incoming (flood) water. As the moon phase is 24hr50min the high and low tide times move forward every day.
Through to the earths’ rotation, different latitudes and underwater topography, we have four types of tides.
The "semi-diurnal" tides "even" and "odd" have two high tides and two low tides every day. The tide "semi-diurnal-even" is the most common one and has the same tide ranges day and night.
"Diurnal" tides are in areas that have only one high tide and one low tide the day.
"Mixed" tides are in those tropical latitudes where some days have two tides and some days only one