tides and currents 3

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Tides and Currents 3/12/11

Robert Trinidad, Jr. March 12, 2011

BSMT-I HC Meteorology and Oceanography

TOPIC: TIDES and CURRENTS

Objectives:

· Define the tide and some terminologies involving tides

· Enumerate and classify the types of tides

· Specify the classes of tides

· Delineate the term current and terms involving currents

Introduction:

Oceanography, also called oceanology or marine science, is the branch of Earth science that studies the

ocean. It covers a wide range of topics, including marine organisms and ecosystem dynamics; ocean

currents, waves, and geophysical fluid dynamics; plate tectonics and the geology of the sea floor; and

fluxes of various chemical substances and physical properties within the ocean and across its

boundaries. These diverse topics reflect multiple disciplines that oceanographers blend to further

knowledge of the world ocean and understanding of processes within it: biology, chemistry, geology,

meteorology, and physics as well as geography.

The study of the oceans is linked to understanding global climate changes, potential global warming and

related biosphere concerns. The atmosphere and ocean are linked because of evaporation and

precipitation as well as thermal flux (and solar insolation). Wind stress is a major driver of oceancurrents while the ocean is a sink for atmospheric carbon dioxide.

Our planet is invested with two great oceans; one visible, the other invisible; one underfoot, the other

overhead; one entirely envelopes it, the other covers about two thirds of its surface.

Body:



Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted

by the Moon and the Sun and the rotation of the Earth.

TYPES OF TIDES

Diurnal Tides

A single high and a single low tide occur each day. They tend to occur in certain areas when the moon is

at its furthest from the equator.

Diurnal tides tend to occur when the moon is furthest from the equator.

Semi-diurnal Tides

Two high and two low waters occur daily and are of relatively similar ranges. This type is more likely to

occur when the moon is over the equator.

Semi-diurnal tides tend to occur when the moon is over the equator.

Mixed Tides

These tides also tend to occur as the moon moves furthest north or south of the equator. They are

typified by large variances in tidal ranges during the two daily tides.

CLASSES OF TIDES

Spring Tides, when the moon is full or new, the gravitational pull of the moon and sun are combined. At

these times, the high tides are very high and the low tides are very low. This is known as a spring high

tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring).

They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon

and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon.

Neap Tides, during the moon's quarter phases the sun and moon work at right angles, causing the

bulges to cancel each other. The result is a smaller difference between high and low tides and is known



Speed

How fast the water is moving in relation to a stationary object (e.g. shore, light house).

Flood Flow

The tidal current is in flood when it is coming from the sea to the shore (tide is coming in, or high tide is

ensuing).

Ebb Flow

The tidal current is in ebb when it is coming from shore and returning to the sea (low tide ensuing).

Slack Water

The point between flood and ebb (or ebb and flood) currents when there is no horizontal movement.

Stand

The point where vertical changes stop as the tide reverses. This is not the same as slack water; this is a

tidal (vertical) occurence, not a tidal current (horizontal) occurence.

Maximum Current

The normal maximum speeds of the ebb and flood currents. This does not include effects of weather or

run off from rain or melting snow, which can significantly effect tidal currents.

Conclusion:

On voyage, a knowledge of the sea depth is very important when traveling near the shore or

approaching a port. Knowledge of these facts about tides and currents could lead to a safe navigation.

This research paper had tackled topics about tides and currents that could greatly affect the ships safety

during voyage.



References:

tides and currents 3

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