Oceanography Part three

internal waves

• larger than surface waves

• caused by tides, turbidity currents, winds, ships

What are internal waves associated with

pycnocline

disturbing force

energy that causes waves to form

How are waves generated

mass movement into ocean, shifts in ocean floor, tides, human causes

wave movement

cyclic motion of particles in ocean

particles move:

• longitudinal

• transverse

• orbital

longitudinal

compress and decompress as they travel, coiled spring

transverse

• side to side waves

• energy travels at right angles to direction of moving particles

• mostly through solids not liquids

crest

highest point

trough

lowest points

wave height (h)

vertical distance between crest and trough

wavelength (l)

horizontal distance from crest to crest or trough to trough

wave steepness

H/L

> 1/7= wave breaks

wave period (T)

time for one wavelength to pass a fixed point

wave frequency

number of wave crests passing a fixed location per unit time, = to inverse of period of 1/T

wave speed

wavelength (L)/ period (T)

orbital

• interface waves, on ocean surface, combo of longitudinal and transverse

• diameter of orbital motion decreases with depth of water

wave base

1/2 L

• depth where orbital movement of water particles stops

• have no interference with the ocean bottom

orbital wave characteristics

• water molecules transmit the wave energy but move in a circle and end where they started

• circular orbits of an object floating on the surface have a diameter equal to wave height

If water depth is greater than wave base (>½L)

wave is a deep-water wave

deep water waves

• wind generated waves in open ocean are deep waves

• speed is function of wavelength

• longer wavelength= faster the wave travels

wave development

• as wind increase height and wavelength do too continuous effect

• three factors affect wave energy: wind speed, duration of wind, fetch

fetch

distance over which the wind is blowing (in a single direction, for a period of time)

Biggest waves occur in

the Southern Ocean

shallow water waves

• water depth is less than 1/20 L

• interaction with seafloor interferes with the circular orbital motion, causing orbits to be flattened

• deeper the water= faster the wave

transitional waves

• both deep and shallow water waves

• depth is greater than 1/20 wavelength but less than ½

constructive interference

waves the same wavelength meet in phase and produce a wave of greater height

destructive interference

out of phase waves the same wavelength meets out of phase and eliminate each other

mixed interference

waves of different wavelengths and heights meet and the result is complicated

interference patterns

collision of two or move wave systems interfering with one another

constructive interference

in phase waves with about the same wavelength

rogue waves

massive spontaneous solitary ocean waves

abnormal heights very destructive

hard to forecast

surf zone

zone of breaking waves near shore

shoaling water

water becoming gradually more shallow

• when deep water waves encounter shoaling water less than ½ their wavelength they become transitional waves

deep water wave becomes a shallow water wave

• wave speed decreases

• wavelength decreases

• wave height increases

• wave steepness increases

• when steepness is greater than or equal to 1/7 wave breaks

spilling breaker

break over long distance occur on smooth sloped shore meh surf

plunging breaker

top of wave outruns bottom creating aur pocket occur over moderately steep sloping shores further out best for surf

collapsing breaker

seafloor has a steep slope and lower part of waves is slowed so rapidly that the leading face of the wave collapses before the crest arrives just no

surging breaker

build up and break right at the shoreline not enough time to reach critical steepness to break occur on shores with abrupt slopes

wave refraction

• wave energy unevenly distributed on shore

• bounced back from barrier

• as wave approaches shore, they bend so wave crests are nearly parallel to shore

orthogonal lines

show direction waves travel

• converge on headlands- more energy released here better for surf

• diverge in bays- energy more displaced in bays

tsunamis

seismic sea waves

• long wavelengths >200km

• encompasses whole water column

• acts as shallow water wave

• more common in pacific

tsunamis origins

• Earthquakes – most common cause

• Underwater landslides

• Underwater volcano collapse

• Underwater volcanic eruption

• Meteorite impact – splash waves

Deep ocean Assessment and Reporting of Tsunamis (DART)

• system of sea floor sensors that pick-up pressure pulses from tsunami above

• relay data to nearby buoy which use satellites to get info to land

tides

periodic raising and lowering of sea level that occurs daily

• act like regular shallow water waves

Why tides?

Issac newtons gravitational explain relationship with lunar cycle

gravitational force

proportional to product of masses

• increase in mass increase in force based on distance

centripetal forces

• center seeking force connects an orbiting body to its parent

• gravity tethers earth and moon to each other

zenith

greatest force

closest to moon

nadir

least force

furthest from moon

resultant forces

• mathematical difference between gravitational and centripetal forces

• significant horizontal component

lunar bulges

result when force pushes water into two simultaneous bulges

• one toward moon

• one away moon

• fixed according to sun and moons positions

• rotation carries specific locations in and out

tide phenomena

tidal period- time between high tides

lunar day- time between two successive overhead moons 24 hrs 50 min

solar day-24 hrs

high tides: 12 hrs and 25 min apart

sun bulge

similar to lunar bulge but smaller

flood tide

water moves toward shore

ebb tide

water moves away from shore

spring tides

new & full moons

tidal range greatest

syzygy

neap tides

quarter moons

tidal range least

quadrature

declination

angular distance above or below the equator

changes between 28.5 north and 28.5 south during year

ecliptic

plane at which earths elliptical orbit around sun is located

Monthly tidal cycle

29.5 days

syzygy

moon, earth, and sun aligned

quadrature

moon in first or third quarter phase

perigee

• moon closest to earth

• tidal range greatest

apogee

• tidal range least

• moon furthest from earth

perigee-apogee cycle

27.5 days

perihelion

earth closest to sun in N. Hemisphere Winter

aphelion

earth furthest from sun in N. Hemisphere

How many high and low tides will a place have a day

two of each per lunar day except at poles

amphidromic point

crests and troughs of tide rotate around

cotidal lines

connect simultaneous high tide points

diurnal tidal pattern

• single high and a single tide each lunar day

• tidal period of 24hrs 50min

semidiurnal tidal pattern

• two high tides and two low tides each lunar day

• tidal period 12hrs 25 min

shore

the zone that lies between the low tide line and the highest area on land affected by storm waves

coast

extends inland as far as ocean related feature are found

coastline

boundary between shore and coast

backshore

part of shore above high tide shoreline

foreshore

part of shore exposed at low tide and submerged high tide

shoreline

water’s edge that migrates with the tide

nearshore

extends seaward from the low tide shoreline to low tide breaker line

offshore

zone beyond low tide breakers

beach

wave worked sediment deposit of the shore area

wave cut terrace

flat wave-eroded surface

berm

dry gently sloping elevated beach margin at the foot of coastal cliffs or sand dunes

beach face

wet sloping surface extending from berm to shoreline

longshore bars

sand bars parallel to coast (might not be present, causes waves to break)

longshore trough

separates longshore bar from beach face

What are beaches composed of?

• local material in transit along the shoreline

• boulder from local cliffs

• sand from rivers

• mud from rivers

swash

water rushes up the beach

backwash

water drains back to the ocean

Light wave activity

• swash soaks into beach so decreased backwash

• creates well developed berm

• movement of sand up beach face

heavy wave activity

• beach saturated from old waves so very little swash soaks in

• backwash dom= sand down beach face= erosion

• eroded sand accumulates in offshore bar

summertime beach

• wide sandy beam

• steep beach face

• swash dominates

• milder storms

wintertime beach

• backwash dominates

• sediment moved away

• stormy weather

• narrower beach

wave refraction

bending of waves from original direction to break nearly parallel to shoreline

refracting waves

move water and sediment up and downcoast

• results zig-zag motion of swash/backwash water and resulting beach sands

longshore current

zig zag movement of water downcoast along shoreline

• speed increases with increasing beach slope, wave energy, and angle of the waves approaching shore

longshore transport (drift)

zig zag movement of beach sands downcast along the shoreline

rip currents

strong narrow current moving directly offshore

form from backwash returning to the ocean under light-moderate swell

• 15-45 m wide

• 7-8 km/h

how to escape rip tide

swim left/right to get out of the narrow rip current then ride waves into beach

depositional shores

where sand deposition exceeds sand erosion

• deposits can be moved around by longshore drift

• modified by other coastal processes