WAVES!!! Draw me a picture of a perfect surfing day! No it doesn t have to be a Rembrandt or Monet just try!

Transcription

1 WAVES!!! Draw me a picture of a perfect surfing day! No it doesn t have to be a Rembrandt or Monet just try!

2 Waves Caused by: Wind Earthquakes Gravitational force of the Moon and Sun.

3 Wave = an undulation of the water surface, usually created by wind 1. crest = high point of a wave 2. trough = low point between two crests 3. wave height = height difference between the trough and crest 4. wavelength = distance between two crests 5. wave period = time taken for two crests to pass a stationary object

4 A simple diagram make sure you have it in your notes

5 The wave period is a very useful parameter in the classification of Capillary waves = small wind generated waves that are most readily seen on flat calm water causes by slight breezes and local winds Wave period = <0.1 second waves

6 The wave period is a very useful parameter in the classification of waves Chop = generated locally these waves are bigger than capillary but relatively small Wave period = 1-10 sec

7 The wave period is a very useful parameter in the classification of waves Swell = created by distant storms wave lengths can be up to hundreds of meters do not necessarily have large wave height Wave period = sec

8 The wave period is a very useful parameter in the classification of waves Tsunami = created by seismic activity wavelength can be up to hundreds of km, can be very distructive, known previously as Tidal Wave Wave period = min

9 Believe it or not the water is staying relatively still as a wave travels the energy is moving. Wave energy travels in a circular path That energy cycle causes the water to rise forming a crest And to fall causing a trough

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11 Progressive waves = wind generated waves You can follow the crest of a progressive wave across the ocean, but what is really moving is the energy!

12 Waves Caused by Wind When wind blows across a body of water, friction causes the water to move along with the wind. Wave Height depends on Wind speed Distance over which the wind blows Length of time the wind blows

13 A steady wind of 56 mph is blowing over an ocean and a bathtub, are the same size waves created in each? Why or why not?

14 The type and size of wind generated waves are dictated by 4 main factors 1. wind velocity = how fast the wind is traveling 2. wind duration = how long has the wind been blowing 3. fetch = the area over of water over which the wind is blowing 4. original sea state = how much wave action already exists a: with old seas = sea state originally had waves and new ones are being added b: without old seas = sea state was originally without waves and new ones are being added

15 The life of a wave fetch = the birthplace of waves, this is where wind comes in contact with the surface and transfers energy to the water, causing waves higher wind speed creates higher and longer waves (more powerful) waves formed by winds in the fetch are not often well organized, they are chaotic and mix of size and celerity

16 The speed of a wave is called CELERITY Celerity = the speed of a wave, this term is used because it is energy moving in a wave, not water (mass) EX. Speed = time it takes a car to get down the quarter mile D/T (mass has been transported) D=distance T=time Celerity = time it takes the energy in a wave to travel a distance L/T (no mass as moved) L=wavelength T=wave period

17 Wave interference = interaction of many waves Waves can either work to strengthen one an other or to destroy each other Constructive interference = wave troughs and crests coincide and create stronger waves Constructive wave interference can cause rogue waves Rogue waves = unusually large waves that are actually constructed of many coinciding smaller waves

18 Fully developed sea = the waves have grown to the largest size that the wind speed will allow Significant Wave Height = the average of the highest third of all of the waves The significant wave height will always be more than the average of all Think of your grades. 100, 100, 80, 75, 75, 50, 50, 50, 25 total average = significant average = 93.33

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21 Destructive wave interference = when the trough of one wave meets up with the crest of another, in effect reducing wave height and length and period, making a weaker wave

22 Dispersion = the wave organization outside of the fetch area. Once waves leave an area of high winds no more energy is being added and the wave properties become stable (Think of the regularity of waves crashing on the shore on a calm afternoon) longer waves having higher celerity will separate from shorter waves and will reach the shore faster than other weaker waves

23 Shallow water waves Shallow water wave = waves in water that is 1/20th the wavelength Deep water wave cycles are unaffected by the sea floor

24 Shallow water waves are changed in three ways 1. shallow water wave interference = waves can feel the sea floor a. waves begin to loose celerity speed (the celerity of all shallow water waves is determined by depth) b. waves begin to slow and bunch up as the sea floor saps their energy (waves travel slowest just prior to breaking) c. wave height begins to grow as the wave pushes up on it s self (think about a crowd trying to push through a small door) one thing that does NOT change WAVE PERIOD.. this property of the wave still remains constant

25 2. Shore breakers = waves that have gotten into shallow enough water to cause them to become unstable a. Spilling breaker = upper part of the crest becomes too steep and spills or sweeps down the front of the wave b. Plunging breaker = the crest of the wave steepens curls over and plunges forward c. Surging breaker = the wave never really breaks instead it rides up the beach smoothly and retreats

26 Spilling Breaker

27 Plunging breaker

28 Tides The rise and fall in sea level is called a tide. Caused by a giant wave. One low-tide/high-tide cycle takes about 12 hrs and 25 min. Tidal range is the difference in ocean level between high-tide and low-tide

29 What is the Tidal Range? HT = 30 ft, LT = 20 ft HT = 20 ft, LT = 12 ft HT = 50 ft, LT = 20 ft

30 Types of Tides Spring: 1 st. and 3 rd. quarters Neap: new and full moon

31 Gravitational Effect of the Moon Two big bulges of water form on the Earth: one directly under the moon another on the exact opposite side As the Earth spins, the bulges follow the moon.

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33 Gravitational Effect of the Sun Spring Tides Earth, Moon, and Sun are lined up High Tides are higher and Low Tides are lower than normal

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35 Gravitational Effect of the Sun Neap Tides Earth, Moon, and Sun form right angles High Tides are lower and Low Tides are higher than normal

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37 St. Michel, N. coast of France ~16.8 m highest tidal range in Nova Scotia

38 Nova Scotia Tides Wolfville, NS (16 m tidal range) Diurnal Tides (one high and one low every 12 hours and 25 minutes