SCM 330 Ocean Discovery through Technology Area F GE

Introduction To Marine Science Goals: Background of the Dynamic Processes at work in the Ocean.

Physical Oceanography Circulation Waves Tides

Physical Oceanography - Circulation Major Ocean Currents

Ocean Circulation Surface Circulation Dynamics Physical Oceanography - Circulation

Surface Ocean Circulation Surface Currents are Wind Driven Physical Oceanography - Circulation

WIND Depth (Z) 2000 m Wind stress + Coriolis + Gravity Drive surface currents Transfer of Energy by friction Physical Oceanography - Circulation

The Ekman Spiral Physical Oceanography - Circulation

How Water is Effected by Wind Physical Oceanography - Circulation

Gyre Formation Physical Oceanography - Circulation

Gyre Formation Physical Oceanography - Circulation

Pressure Within A Gyre Physical Oceanography - Circulation

Equatorial Current Dynamics Physical Oceanography - Circulation

Water piles up the equator due to NEC and SEC Equatorial Current Dynamics Physical Oceanography - Circulation

Largest Current ( sv) Feeds the Peru (Humbolt) and Benguela Currents Antarctic Circumpolar Current Physical Oceanography - Circulation

Differences Between Western and Eastern Boundaries Physical Oceanography - Circulation

Western Boundaries Physical Oceanography - Circulation

N. America Africa Differences Between Western and Eastern Boundaries Physical Oceanography - Circulation

Speed of Gulf Stream Physical Oceanography - Circulation

sv // 250 cm/s The Gulf Stream: sv at Florida (narrow and shallow) sv at Cape Hatteras (wide and deep) Physical Oceanography - Circulation

Kuroshio Western Boundary Physical Oceanography - Circulation

Small Scale Dynamics: Langmuir Cells Up to ~ 2 km long Physical Oceanography - Circulation

Langmuir Cells Physical Oceanography - Circulation

Ocean Circulation Deep – Driven by Differences in Density (Thermo-haline Circulation) Physical Oceanography - Circulation

Thermo-haline Circulation Drives deep, ocean circulation, affecting almost 90% of Ocean’s total volume Temp and Salinity affect density of water masses. Density  as Temp  and Salinity  Deep Water Intermediate Mixed Physical Oceanography - Circulation

Density differences Physical Oceanography - Circulation

Mixing Dynamics Physical Oceanography - Circulation

Density Temperature Physical Oceanography - Circulation

Important Water Masses Physical Oceanography - Circulation

Conveyer Belt Circulation Can take 1,000 years to complete a lap Physical Oceanography - Circulation MOVIE

El Niño (Southern Oscillation) Physical Oceanography - Circulation

Normal Conditions El Nino Conditions Physical Oceanography - Circulation

Physical Oceanography - Waves Waves Wave Movement Wave Characteristics Wind-Generated Waves Tsunamis Internal Waves

Where do Waves Come From? Waves that travel long distances from the storm are Swell Waves large weather systems and winds blow across water and cause waves Physical Oceanography - Waves

Development of Sea and Swell At the source, the wind pushes up large waves, called a forced sea As the waves travel away from the source, the wind no longer pushes them up, so they become smoother, shorter (called dispersion), and longer wavelength, and are called a swell Physical Oceanography - Waves

Wave Train A group of swell waves traveling together form a Wave Train Wave trains travel away from the storm center Travel distance depends on wind energy generated by the storm Short period waves damp out with distance, leaving longer period waves; so near a storm you see a mixture of long and short period swells, but only long period at a distance Physical Oceanography - Waves

Wave Motion Waves move by the transmission of energy by cyclic movement through matter The medium itself (water) does NOT travel Wave motion is NOT water FLOW, but is a flow of energy Progressive Waves Can be longitudinal (push-pull), transverse (side to side), or orbital (interface waves) Orbital waves are the most common type at the sea surface Transmit energy along the interface of two fluids of different density (water and air) Physical Oceanography - Waves

Particle Motion Movie Physical Oceanography - Waves

Wave Characteristics Wavelength (L) = horizontal distance between successive peaks or troughs Wave height (H) = vertical distance between peak and trough Crest = top of waveTrough = bottom of wave Frequency (f) = number of wave crests passing a point in unit time (second) Period (T) = time required for wave crest to travel one wavelength Steepness (S) = ratio of wave height to wavelength (H/L) Speed = wavelength divided by period (L/T) Direction of motion Physical Oceanography - Waves

More Wave Characteristics There is a slight net movement of water in the direction of the wave because particle speed decreases with depth Deep-Water Waves occur where water depth (d) is greater than L/2 Are not affected by ocean floor Speed is determined by L and T T easiest to measure, so speed is calculated by S = 1.56*T This applies to most wind waves Physical Oceanography - Waves

Speed of Deep Water Waves Determined by Wavelength Physical Oceanography - Waves

Wave Summary Physical Oceanography - Waves

Shallow & Transitional Waves Shallow-water Waves occur where the water depth (d) is less than 1/20 of the wavelength (L) Includes wind waves that move inshore, tsunamis (seismic waves),and tides (tide waves) Speed equals 3.1 times the square root of the depth in meters, S = 3.1 *  d Particle motion is in the form of a flat, elliptical orbit Transitional Waves (20d < L < 2d) speed is controlled by wavelength and water depth Physical Oceanography - Waves

Shallow & Deep Water Waves Graph shows how wave speed depends on wavelength and whether a wave is shallow or deep water variety Deep water wave speed determined by wavelength Transitional waves are a combination Shallow water wave speed determined more by depth Physical Oceanography - Waves

Wind Generated Waves Capillary Waves - the smallest waves formed at the lowest wind speeds The restoring force (the force that pulls wave down) is surface tension Gravity Waves - the next stage of waves formed by increasing wind speeds Named for their restoring force (gravity) Increasing energy from wind increases wave height, length, and speed Physical Oceanography - Waves

Factors That Increase Wave Energy Major Factors that Increase Wave Energy Wind Speed Duration - amount of time that wind blows in one direction Fetch - the distance over which wind blows in a single direction Fully-Developed Sea - when the maximum fetch and duration are achieved for a given wind speed Physical Oceanography - Waves

Breakers & Swells Open-ocean Breakers (Whitecaps) form when wave steepness exceeds 1/7 of the wavelength (H=1/7L) Swells - waves that move toward the ocean margin and away from the wind source Swells become long-crested waves that may travel great distances with little loss of energy (as much as 8,000 miles!) Ocean Breakers Swells Physical Oceanography - Waves

Interference Occurs when two (or more) waves collide Produce the algebraic sum of the individual disturbances Constructive - waves are in- phase and add crest to crest and trough to trough (waves get bigger!) Destructive - waves are added crest to trough (waves get smaller) Mixed - a combination of constructive and destructive (most common) Physical Oceanography - Waves

Rogue Waves Very rare large waves, probably due to unusual constructive interference Most frequent downwind from islands or shoals where storm waves encounter strong ocean currents Very dangerous to shipping or people on the shoreline Can be up to m tall (8 story building!) Physical Oceanography - Waves

Rogue Waves Artist’s depiction of fishing boat in 100-ft “perfect storm” wave Physical Oceanography - Waves

Surf The energy stored in swells is released in the surf zone and breakers form Occurs when deep-water waves eventually reach shallow depths that are less than 1/2 their wavelength (L/2) Friction removes energy from the waves and wavelength decreases in the surf zone Wave height increases and when steepness (H/L) reaches 1/7 (water depth of 1.3H), the wave breaks as surf When depth <1/20 of the wavelength, waves behave as shallow waves and encounter bottom friction Physical Oceanography - Waves

Surf Drawing shows how wave height increases, wavelength decreases, so the wave becomes steeper and breaks Physical Oceanography - Waves

Wave Refraction Wave Refraction - bending of a wave front Waves seldom approach a shoreline at 90° angle Part of the wave that contacts bottom is bent or refracted Orthogonal lines of equal energy are always bent toward shallower water Energy often focused on headlands Bays receive lower, dispersed energy that may enhance sediment deposition Physical Oceanography - Waves

Wave Refraction Toward Beach Even though waves approach from oblique angle, refraction bends them nearly perpendicular to the beach Physical Oceanography - Waves

Wave Diffraction Wave Diffraction - bending of waves around objects Bending occurs on a smaller scale than refraction Any point on a wave front can be a source which can propagate in any direction Physical Oceanography - Waves

Tides Topics General Features Generating Tides Equilibrium Theory of Tides Dynamical Theory of Tides World Tides Power from Tides Physical Oceanography - Tides

General Considerations  Tides are basin-scale waves caused by attraction of Sun and Moon  Tides are the ultimate in shallow-water waves wavelengths = thousands of kilometers wave heights > 15 meters (45 ft)  Occur with a regular, predictable periodicity  Are most noticeable along coastlines because of fixed reference points  Tides are measured in terms of water height relative to a tidal datum  Tidal Datum is the zero depth reference and usually equal to the average depth at low tide (mean low water) - this is the water depth usually printed on coastal navigation charts Physical Oceanography - Tides

Tide Gauge Tides are measured at stations with device called tide gauge Physical Oceanography - Tides

Solar vs. Lunar Tide The Sun has 27 million times greater mass than the Moon But it is located 390 times farther away, which reduces the tide by 59 million times Thus the solar tide is only 46% of the lunar tide Physical Oceanography - Tides

Ideal Tide Ideal tide has two bulges on opposite sides of Earth along Earth-Moon line As Earth rotates, observer not at poles (where tide zero) would see two high tides (the bulges) and two low tides (90° from bulges) go by each day Max at equator Bulges would act as large waves traveling around the Earth Departures from ideal Earth-Moon not lined up 90° from rotation axis Friction Water not uniform depth Continents get in the way Actual tides are more complex because situation not ideal, so we introduce more concepts Physical Oceanography - Tides

Lunar Day Lunar day is 50 minutes longer than solar day Earth rotates in 24 hours, but Moon moves around Earth through 12.2° of its orbit, which requires an extra 50 minutes of rotation to catch up This means ideal tide would occur twice every lunar day (12 hr + 25 min) Thurman & Burton Physical Oceanography - Tides

Spring Tide & Neap Tide Solar and lunar tidal bulges move around Earth according to positions of two bodies Both tides simply add to give net tide Maximum tide (Spring tide) when Sun and Moon lined up (new Moon and full Moon) Minimum tide (Neap tide) when Sun and Moon at 90° angle Approximately 2 weeks between spring and neap tides Physical Oceanography - Tides

Cheesy Tide Animation Physical Oceanography - Tides

Solar and Lunar Tides Add Spring tide Neap tide In between tide Physical Oceanography - Tides

Solar Declination Earth’s rotation axis is tilted but stays pointed toward same point in space Therefore sun’s angle overhead changes Sun overhead at equator at equinoxes (March 21, Sept 23) Sun farthest north June 21 and farthest south December 22 Means that solar tide bulge will be max at different latitudes at different dates Physical Oceanography - Tides

Lunar Declination Moon’s orbit tilted 5° from Earth’s orbit This means that Moon moves in declination also Maximum difference is 28.5° (spin axis tilt 23.5° + lunar orbit tilt 5°) This factor means that lunar tide bulge will move N and S of equator Physical Oceanography - Tides

Predicted Equilibruim Tide When we include the effect of lunar declination, here’s what a tide sequence would look like Observer at 28°N sees highest tide at 0 hr and lower high tide at 12 hr Observer at equator sees two nearly equal high tides Observer south of equator sees highest tide at 12 hr San Francisco tide record below shows variations in tide over month Physical Oceanography - Tides

Dynamic Theory of Tides And yet more complicating factors Tides are shallow water waves Friction with bottom Speed varies because of varying water depth Instead of moving 1600 km/hr (to pace Moon), actual velocity is ~700 km/hr so tides lag Moon & Sun Continents get in the way (disrupt the tidal wave) Coriolis effect (you didn’t forget that, did you?) Tide scientists have built complicated models using both theory and observations (because math model not perfect) Model is sum of many tidal waves with different sources and periods Physical Oceanography - Tides

Amphidromic Points Actual tidal waves rotate around null points (no tidal range) called amphidromic points (this map for lunar L2 tide) Lines radiating from AP are cotidal lines, show crest of tide wave at different hours Tide range shown by colors (highest = red & purple) APCL Physical Oceanography - Tides

Three Tide Types Because of all the various factors, there are three different types of tides Diurnal = one high + one low per day with about equal amplitudes Semi-diurnal = two highs + two lows per day with about equal amplitudes Mixed = combination of high + low tides of different heights (common) Physical Oceanography - Tides

Map of Tide Types Physical Oceanography - Tides

Changing Tides Note how tide changes with time of month and phase of moon Note differences in amplitude between successive spring tides Physical Oceanography - Tides

Tidal Power Tides move much water up and down tidal estuaries Moving water can provide energy when dammed up Tidal power plant allows incoming tide to push turbines, then turbines reverse and make power as tide moves out Trouble is slack and slow waters around high and low tide Tide power plant from St. Malo, France Physical Oceanography - Tides