Waves and Water Dynamics

Waves and Water Dynamics

Waves and Water Dynamics Essentials of Oceanography Pebble in Still Water What happened when I dropped the pebble into the still tank? How do the particles move at the point of disturbance? How does the cork move? http://www.brighthub.com/education/k-12/articles/39375.as

px#ixzz1A5lRdeRe Cork in the disturbance How does the cork move? What Causes Waves? Waves are created by releases of energy (disturbances) including:

Wind Movement of fluids of different densities Mass movement into the ocean (splash waves) Underwater sea floor movement (tsunami) Pull of the moon and sun (tides) Human activities Most Ocean Waves Are Wind-generated

Anatomy of a Wave Crest- maximum elevation about still water level Trough- max depression below still water level Wavelength (L)- crest to crest, or trough to trough Height (H)- vertical distance crest to trough Amplitude- H/2, still water to crest or trough Period (T) - time for one wavelength to pass a

point Frequency number of wave crests passing a point in 1 second Anatomy of a Wave Wave Characteristics and Terminology (Continued)

Wave speed frequency x wavelength 1 1 Frequency ( f ) or Period (T) T f Period (T) = the time it takes one full wave one wavelengthto pass a fixed position

How do waves move? 1. The direction of propagation of wave, that is, the direction in which the disturbance travels. 2. The disturbance is transferred due to the oscillation of the particles of the medium involved. The direction of these oscillations is the second direction. Types of Progressive Waves Longitudinal

Back-andforth motion Transverse Side-to-side motion Orbital Combination

Circular Orbital Motion As a wave travels, the water passes the energy along by moving in a circular orbit Floating objects also follow circular orbits

Orbital Motion in Waves Orbital size decreases with depth to zero at wave base Depth of wave base = wavelength,

measured from still water level Tides Essentials of Oceanography What Causes Tides? Tides are created by the imbalance between two forces:

1. Gravitational force of the moon and sun on earth If mass increases (), then gravitational force increases () If distance increases (), then gravitational force greatly decreases ()

2. Centripetal (center-seeking) force required to keep bodies in nearly circular orbits Tides Equilibrium Theory of Tides (Newton) Assumes earth covered by uniform layer of water

No effect from: Interaction with the seafloor Influence of basins (land) Sloshing Contrasts to Dynamic theory of Tides (Laplace) Gravitational Forces on Earth Due to the

Moon Force decreases with increasing distance Force is directed toward the Moons center of mass

Resultant Forces Creates 2 bulges in the ocean (~2m) At the center of mass 0 tractive force On the side facing the moon- gravitational force = 1 bulge On the side away from

the moon- inertial force = 1 bulge Tidal Bulges Solid Earth = small response to these forces (10-12) Oceans and atmosphere = fluids = greater response to forces (ocean = ~2m/ atm = miles) Bulges tend to stay aligned with the moon as Earth spins

Earth turns beneath the bulges Tidal Bulges Tide-generating forces produce 2 bulges: 1. 2. Away from moon on side

of earth opposite moon Toward moon on side of earth facing moon Earth rotates into and out of tidal bulges, creating high and low tides Figure 9-6

The Lunar Day Tidal bulges follow moon as it revolves around earth Lunar day is 50 minutes longer than a solar day because the moon is moving in its orbit around earth Tidal cycle is 12 hrs. 25 min. Add the Sun Tide generating force of the sun also a factor, but

less important than the moon m1m2 T G r3 Sun is 27,000,000x more massive than moon Sun is 387 X farther away than the moon (3873 = 58,000,000) effect of the sun = 27 million/58 million = .46

= Effect of sun = 46% effect of moon (~1/2) Sun also creates a tidal bulge, but smaller than the bulge from the moon Relative Sizes and Distances on Earth, Moon, and Sun The sun is much more massive

than the moon but much further away Solar bulges are 46% the size of lunar bulges The Monthly Tidal Cycle (29 Days)

About every 7 days, Earth alternates between: Spring tide Alignment of Earth-Moon-Sun system (syzygy) Lunar and solar bulges constructively interfere Large tidal range Neap tide Earth-Moon-Sun system at right angles (quadrature) Lunar and solar bulges destructively interfere

Small tidal range Earth-Moon-Sun Positions Combined Tides When sun-moon-Earth aligned (new or full moon) Solar tide added to lunar tide Max high tides and min low tides Spring tides

When sun-moon-Earth at right angles (first and last quarter) Solar trough coincides with lunar crest (and visa versa) High tides not very high Low tides not very low Neap tides Combined Tides

Dynamic Theory of Tides Equilibrium model- idealized Dynamic model- add landmasses, ocean basins, friction ~150 tide generating/tide altering forces- very complicated Cant predict tides mathematically Tide charts based on studies of past patterns Dynamic Theory of Tides

Basin Effects Water can slosh back and forth in a basin Tides can resonate across a basin, shape of the margins can affect the rhythm Tidal Patterns Diurnal One high and one low tide each (lunar) day

Semidiurnal Two high and two low tides of about the same height daily Mixed Characteristics of both diurnal and semidiurnal with successive high and/or low tides having significantly different heights

Tidal Patterns http://tidesandcurrents.noaa.gov/station_retrieve.shtml?type=Tide+Data Monthly Tidal Curves Tidal Range Varies with the shape of the basin Extremes develop where inlets focus tidal energy and

Water resonates at frequency of tidal cycle The Bay of Fundy: Site of the Worlds Largest Tidal Range Tidal energy is focused by shape and shallowness of bay Maximum spring

tidal range in Minas Basin = 17 meters (56 feet) Bay of Fundy http://faculty.gg.uwyo.edu/heller/SedMovs/bayofun1.htm

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