Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
☰ Search Explore Log in Create new account Upload × MAY 2011 Oceanography Ch # 9. TIDES The periodic rising and falling of the average Sea Level. Tides are regular, very long, thousands of miles , shallow water waves, , max 50 ft. high. First explained by Newton. The Universal Law of Gravitation – every particle of mass attracts every other particle in the Universe. 9 – 1. Causes of Tides. Tides are generated by forces imposed on the earth by the Sun and the Moon (gravitational attraction). The resultant force (difference between the Gravitational and Centripetal) causes tidal bulges on earth, and generates the tides. Gravitational and centripetal forces keep the planet in orbit. Tidal Bulges. As a result of primarily the Moon’s gravity pull, there are two bulges on opposite sides of the earth, around the equatorial region. Most places should experience two hi tides every 12 hr and 25 mins, based on the lunar day (24 hs and 50 mins). Solar effect. – bulges are much smaller than the lunar bulges. (distance from the earth and size of the sun) Earth’s rotational effect - as the earth spins, locations move in and out of the tidal bulges. The max tide is called the Flood tide (Spring) and the lowest tide is the Ebb tide. 9 – 2. How Tides vary during the monthly tidal cycle The monthly cycle is 29.5 days. (how long it takes for the moon to go around the earth). There are 4 phases during the monthly cycle, namely: New Moon – moon is located between the sun and earth. First and 2nd. Quarters – A line drawn from the moon to the earth, and one from the sun to the earth form a right angle. Full Moon - Earth is located between the sun and the moon. When gravitational forces are lined up, the forces are added to each other (Constructive) and tides are very high. (Spring Tide) The opposite is Neap tide when the forces are destructive. Complicating Factors are: Declination of the Moon and Sun. Orbits are elliptical. Distance varies by 2.5% The max tide occurs when earth is closest to the Sun (Perihelion) and closest to the moon. 92.2 Mmiles – 94.5 M miles. January each year. Earth’s tilted axis 23.5 Deg Moon’s orbit relative to the earth is 28.5 Deg. Its tilt is 5. Deg. Elliptical orbit. Variation is 8%. (375,000 km –Perigee, to 405,000 km- Apogee) Effects of Elliptical Orbits. Earth’s distance from the Sun varies 2.5%. The max tide occurs when earth is closest (Perihelion and Perigee resp.) to the Sun and to the Moon. Predicting Tides. The declination of the Moon determines the position of the Tidal Bulges, directly over the 28 Deg N or S Latitudes. 9 – 3. Tides in the Ocean. Tidal bulges are 20,000 km apart – one half the earth’s circumference. The wave speed is affected by depth. Ocean avg. depth is 3.6 km. To be free of interference, depth must be in xs of 22 km. The tide breaks up into units – Cells, the center of each is called the AMPHIDROMIC point. The crest and trough of the wave (tide) rotate around the amphidromic point. A line joining points where the tides are the same height, is called a COTIDAL LINE. In the Northern hemisphere, waves rotate clockwise. A complete rotation occurs once during a tidal period – 12 hrs. Continental effects. They interrupt free movement of the bulges. Their location and shape of coastlines modify the waves. Other factors are sea floor topography, and water temperature. In addition, there are more than 400 other factors. A mathematical model is used to determine the exact time of the tides. Types of Tidal Patterns. Theory: Should be 2 highs and 2 lows (tides) every day. In reality, there are three patterns, which depend on location. Diurnal - GOM ; SE Asia. 1 High and 1 Low tide daily Semi diurnal – Atlantic US Coast. Two high and two low tides Mixed Tidal Pattern – Pacific NA Coast. The most common in the world. Successive high tides have significantly different heights. 9 – 5. Tidal Phenomena in Coastal Regions. When tides enter coastal waters, they are subjected to Reflection Amplification. – Can produce a standing wave phenomenon Large lakes and Rivers also experience tidal phenomenon. Tidal bores affect ecosystems and their inhabitants. An extreme example is: The Bay of Fundy. It has the largest tidal range (17 meters). Coastal Tidal Currents. Currents that accompany the slow turning wave crest in the Northern Hemisphere basins rotate counter-clockwise and produce a Rotary Current. Friction increases in the shallow water, and the rotary current changes to a reversing current. These latter currents are common at the mouth of bays. Whirlpools A rapidly spinning body of water. A vortex occurs in shallow passages connecting two large bodies of water, that have different tidal cycles. Flow rates 10 – 16 km/hr. Ex: the Maelstrom on the west coast of the arctic Norway. 9 – 6. Can Tidal Power be Harnessed as a source of Energy? Boston in the 17th and 18th. Century To generate Power – initially more expensive than Oil or Gas plants. Drawbacks – Harm to wild life Rance River , one of few operating Tidal Power plants in the world. Download 1. Science 2. Earth Science 3. Oceanography Ocean Ch # 9 Tides.doc Chapter 10: Tides Fig. 10-6 Fig. 10-7 Tides Powerpoint Chapter 9: Tides Tides chapter 10 R Topic 17 notes - The University of West Georgia class handout Tides lecture notes Where did the term “lunacy” come from? Chapter 8 Tides Tides studylib © 2017 DMCA Report