Tides and tidal currents
What are tides?
They are the periodic rise and fall of the water level in the ocean and other large bodies of water due to gravitational interaction between the sun, moon and earth.
General Definition: The tide is a deformation of a planet’s surface, produced by the gravitational action of one or more celestial bodies.
Tide generating forces proced 2 tidal bulges:
- Toward moon on side of earth facing Moon;
- Away from moon on side of Earth opposite Moon.
Earth rotate in and out of tidal bulges, creating high and low tides.
High tide are aligned under the moon
Low tide are aligned at a right angle to the high tides.
The tides causes changes in the depth of the sea and produce oscillating currents know as tidal streams, making predictcion of tides is important for coastal activities and navigation. The stripes of seashore that is submerged at high tide and exposed at low tide, the interdital zone, is an important ecological product of ocean tide.
They present three types of tide divided by the influence that the astras exert on the earth’s surface:
Spring T. :
Spring tides are the result of the sun moon and work together to exert greater traction on the oceans of the earth. When the moon is in its full phase and new earth, the sun and the moon are all aligned. This extra gravity pulling at the same point of the ground causes high and low tides strong. The tides are called tidal tides not because of the season, but because the tides are rising strong up and down.
Neap T. :
Quadrature tides are the result of moon and sun processing against any other shooting. When the moon is in its first and third stage fourth, the sun and moon are at right angles to each other. Although the attraction of the moon is stronger, the gravitational attraction of the sun is diminishing the effect of the moon’s gravitational force on the oceans. This means that twice a month we experience high and low tides smaller than normal.
Extreme T. Proxigean:
Spring Eides are extreme high tides During the new phase the moon is on the same side of the earth as the sun. Normally, the difference between this spring tide and that with the full moon, when the earth is between the sun and the moon, is negligible. However, when the moon comes closest to the ground called its proxigee and coincides with a new moon this extra boost of gravity results in an extreme high tide called Proxigean Spring Tide.
The actual sea level amplitude is also dependent on meteorological phenomena that are not related to tides, but that enhance its effects. In particular, the effects of the wind (blowing towards the coast raises the sea level on the coasts, blowing down to lower the level at the coasts) as well as atmospheric pressure differential between the open sea and the coastal zone. The phenomenon of tide resonance, well documented in Fundy Bay, is due to the fact that the tidal wave is reflected from the shore of a bay and meets the next wave of tide coming from the ocean. In this way, the two waves sum up forming particularly strong tidal amplitudes. The opposite case occurs when the reflected tidal wave meets the tidal wave offset (the tidal maximum meets the tide minimum or vice versa), making the sea level variations low.
Tidal effects due to strains The internal seas (such as the Mediterranean Sea) do not show strong tides; on the other hand, tides are of great importance close to the straits (such as the Strait of Gibraltar) as they create strong alternating currents between the ocean and the inland sea, favoring as well as a replacement of the sea water. An even more interesting effect can be highlighted in the Strait of Messina where the tides develop currents (so-called tide) that run periodically (about every 6 hours) first along a narrow sense and then in the opposite direction (current “upright” and current “descending”, depending on the source from the south or north).