ocean tide ppt pragati.pptx

Fisheries oceanography

1. DEPARTMENT OF AQUATIC ENVIRONMENT MANAGEMENT SUBJECT- FISHERIES OCEANOGRAPHY (512) TOPIC:- OCEAN TIDES Presented by Pragati inwati mfk2112

2. OCEAN TIDE INTRODUCTION Tides are produced by the attractions of the moon and sun on the waters of the ocean. They occur in the ocean as progressive or standing long waves. Among all the oceanic long waves, tides are of maximum importance for people living near the sea shore and for those travelling the sea. The rise and fall of the tide is a continues phenomenon and varies from day to day and from place to place.

3. DEFINITION- Tides are bulges of water produced by the gravitational attraction of the Sun and Moon on the ocean and by the centrifugal force resulting from rotation of the Earth –Sun and Earth-Moon systems.

4. Gravity  is the force of attraction between two bodies. The greater the mass and smaller the distance, the stronger the gravitational attraction. G α M1M2/d2 Where G is gravity M1 and M2 represent the mass of body 1 and body 2 and d is distance between the center of the two masses.

5. Tide changes proceed via the following stages: Sea level rises over several hours, covering the intertidal zone,  flood tide . The water rises to its highest level, reaching  high tide . Sea level falls over several hours, revealing the intertidal zone, ebb tide . The water stops falling, reaching  low tide .

6. Cause of tides The gravitational pull of the Moon. Gravitation pull of Sun. Centrifugal force, the force that works as a counterbalance of gravity. Gravitation pull and centrifugal force are responsible for the creation of two major tides on earth. On the moonward side of the earth, tidal bulge is caused by the gravitational pull from the Moon, and the opposite side of the earth's bulge caused by centrifugal force.

7. Highest tides experienced on Bay of Fundy in Canada; it is approx 15-16 m high. The highest tide in India is recorded at Okha, Gujarat.

8. Types of Tides Tides vary in their frequency, direction and movement from place to place and also from time to time . Tides may be grouped into various types based on their frequency of occurrence in one day or 24 hours or based on their height . Tides based on Frequency Semi-diurnal tide Diurnal tide Mixed tide

9. Semi-diurnal tide A semi-diurnal tidal cycle is the one with two nearly equal high tides and two low tides each day . The successive high or low tides are approximately of the same height. The interval between the high and the low tides is of around 12 hours and 25 minutes . Semi-Diurnal Tides are most widespread in the Indian Ocean. 

10. 2. Diurnal tide There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.

11. 3. Mixed tide Tides having variations in height are known as mixed tides. These tides generally occur along the west coast of North America and on many islands of the Pacific Ocean.

12. Tides based on the Sun, Moon and the Earth Positions The height of rising water (high tide) varies appreciably depending upon the position of sun and moon with respect to the earth.  Spring tide Neap tide

13. Spring tides The position of both the sun and the moon in relation to the earth has a direct bearing on tide height. When the sun, the moon, and the earth are in a straight line, the height of the tide will be higher. These are called spring tides and they occur twice a month, one on the  full moon period and another during the  new moon period.

14. 2. Neap tides When the Moon is at first quarter or third quarter, the  Sun and Moon are separated by 90°  when viewed from the Earth. The Moon’s attraction, though more than twice as strong as the sun’s, is diminished by the counteracting force of the sun’s gravitational pull. Normally, there is a seven-day interval between the spring tides and neap tides. Like spring tides, these tides also occur twice a month.

15. Magnitude of tides based on Perigee and Apogee of moon Once in a month, when the moon’s orbit is closest to the earth  (perigee), unusually high and low tides occur. During this time the tidal range is greater than normal. Two weeks later, when the moon is farthest from earth  (apogee) , the moon’s gravitational force is limited. The tidal ranges are less than their average heights.

16. Magnitude of tides based on Perigee and Apogee of earth When the earth is closest to the sun  (perihelion), around 3rd January each year, tidal ranges are also much greater, with unusually high and unusually low tides. When the earth is farthest from the sun  (aphelion) , around 4th July each year, tidal ranges are much less than average.

17. Fig. Magnitude of tides based on Perigee and Apogee of moon

18. Importance of Tides Navigation Fishing Desilting 4. Tides are used to generate electrical power

19. Characteristics of Tides The tidal bulges on wide continental shelves have greater height. In the open ocean tidal currents are relatively weak. When tidal bulges hit the mid-oceanic islands they become low. The shape of bays and estuaries along a coastline can also magnify the intensity of tides.

20. Funnel-shaped bays greatly change tidal magnitudes. Example: Bay of Fundy - Highest tidal range. The large continents on the planet, however, block the westward passage of the tidal bulges as the Earth rotates. Tidal patterns differ greatly from ocean to ocean and from location to location.

21. Impact of Tides Tides raise the level of seawater and hence exposes a large part of the ocean for erosion. It is helpful for the tidal ports that have shallow water which is a constraint for the big ships to enter. Tidal currents are a very potential source of tidal energy which is harnessed by many developed countries on a very large scale and to some extent in India as well.

22. 5. It can be devastating in cases where the tide gets too huge and results in the flooding of the nearby coastal regions. 6. Tides are very helpful for ecosystems such as the mangrove forests and coral reefs to grow and sustain.

23. Tidal Bore A tidal bore is a large wave or bore caused by the constriction of the spring tide as it enters a long, narrow, shallow inlet. The in and out the movement of water into a gulf through channels called a tidal current.

24. Impact of Tidal Bore Tides are stable and can be predicted. Tidal bores are less predictable and hence can be dangerous. The tidal bores adversely affect the shipping and navigation in the estuarine zone. Tidal bores of considerable magnitude can capsize boats and ships of considerable size.

25. Strong tidal bores disrupt fishing zones in estuaries and gulfs. Tidal bores have an adverse impact on the ecology of the river mouth. The tidal-bore affected estuaries are the rich feeding zones and breeding grounds of several forms of wildlife.

26. Reference oceanservice.noaa.gov