Physical Oceanography Flashcards
% of water that the ocean holds
ice
ground water
97.6–> 137010^6km3
2.1
0.5
rest <0.001
Unique properties of seawater
High heat capacity- raise temp of 1g by 1degrees
greater solvent power than any other substance
Why is temperature important
reflects
the amount of heat held and transported by
the ocean.
temperature range in ocean
-2–28
The temperature of the ocean is primarily
influenced by
the heating at the air-sea
interface
define thermocline
a steep temperature gradient in a body of water such as a lake, marked by a layer above and below which the water is at different temperatures
Salinity
Total dissolved solids (mainly sodium chloride,
or “table salt”)
- About 3.5% by weight (average seawater)
- Usually expressed as 35 0/00 (parts per
thousand, ppt or practical salinity units, psu)
- Varies geographically according to
Evaporation, precipitation, rivers, ice
formation and ice melt.
Evaporation versus precipitation
evaporation generally exceeds precipitation
The balance is restored by rain over the
continents, returning water via rivers
Define halocline
a well-defined vertical salinity gradient in ocean or other saline water.
define density (p)
Density is the mass of sea water per unit volume.
Density depends on
Density depends on salinity, temperature and
pressure.
- Density increases with increasing salinity
- Density increases with decreasing temperature
• Seawater density ranges from 1021 – 1070 kg/m³
,
the average density is 1025 kg/m³
increases with pressure
lighter water is
- warmer
- less saline
- shallower
denser water is
colder
• more saline
• deeper
define pycnocline
layer in an ocean or other body of water in which water density increases rapidly with depth
NADW
AABW
North Atlantic Deep Water
Antarctic Bottom Water
3 defining characteristics of GFD
Geophysical Fluid Dynamics
aspect
ratio, stratification, and rotatio
Oceans aspect ratio is large or small
large
horizontal/ vertical scale
like a piece of paper
The Coriolis force (rotation force)
• acts at right-angles to the actual direction
of water motion.
• causes water to move to the right in the
northern hemisphere
• causes water to move to the left in the
southern hemisphere.
How do surface winds drag the ocean
friction
surface winds are
a source of energy for the ocean
The extent to which the wind drags the surface
water depends on:
- wind strength
- wave conditions
- density stratification
give an example of an energy sink
friction- causes mixing in the ocean
Interior friction
depends on the density and the
currents
•Bottom friction
depends on the bottom currents
and the bottom roughness
Ocean pressure
is the weight of seawater per unit area mainly a function of depth Pressure in the ocean increases at a rate of about 1 “atmosphere” per 10 m of water
Pressure=
Heightdensityg
Pressure gradient force
occurs when there is a horizontal pressure difference
high to low p
Explain Ekman transport
• When the wind blows on the ocean, the wind drags the
surface layer with it.
• Rotation causes the surface layer to deflect to the right
(NH) and move at 45o to the wind direction.
• Interior friction causes the surface layer to drag on the
layer below.
• Rotation causes this layer to again deflect to the right
(NH).
• The resulting currents are called Ekman transport
geostrophic balance and the
resulting current is referred to as a geostrophic current
• Suppose we have a difference in sea-level height. Water
will be accelerated from the region of high pressure
towards the region of low pressure.
• As the water starts to move, the Coriolis effect (rotation)
deflects the water to the right (NH) or left (SH).
• The water keeps getting deflected until the force due to
the pressure difference balances the Coriolis force.
Most of earth’s surface wind energies is concentrated in
the easterlies and westerlies
Gyre
Due to wind-generated pressure differences and the
Coriolis effect water typically moves in a circular
pattern
effects of ocean currents
transfer heat from tropical to polar regions
•influence weather and climate
•distribute nutrients
Upwelling
refers to the process where deeper, colder, and
potentially nutrient-rich water is brought to the
surface
Why is upwelling important
it uplifts nutrients to depths where there is light
(recall that both light and nutrients are needed for
photosynthesis to occur).
more nutrients at greater depth
Equatorial upwelling
The winds are predominantly easterly (or westward)
along the Equator.
• In the southern hemisphere the Ekman transport is to
the left of the wind.
• In the northern hemisphere the Ekman transport is to
the right of the wind.
• This corresponds to a divergence in the Ekman transport
at the equator and results in equatorial upwelling
Wind-driven coastal upwelling
In coastal regions, when the wind blows parallel to the
coast the Ekman transport is either directed onshore or
offshore.
• When the Ekman transport is offshore, upwelling results.
• The offshore Ekman transport is “balanced” by an
onshore flow below the surface Ekman layer.
• As a result, colder water is uplifted to the surface.
• When the Ekman transport is onshore, downwelling
results. This is the opposite to upwelling
Spring Tides
Occur When the Moon Pulls along the same Line as the Sun. (new and full moon).
Neap Tides
Occur When the Moon Pulls at 90o to the Sun (first and last quarter moon)
Tidal waves
have wavelengths (L) on the order of
1/2 the diameter of the earth or about 20,000 km.
• Since the ocean is about 4km deep, and since
L/20 is about 1000km, tidal waves are shallow
water waves
What are waves (4 points)
A wave transfers a disturbance from one part of a
material to another
2. The disturbance is propagated through the material
without any substantial overall motion of the material
itself.
3. The disturbance is propagated without any significant
distortion of the wave form.
4. The disturbance appears to be propagated with constant
speed (unless fluid depth is shallow and changing).
what is being transported by a wave
energy
Surface waves
Waves which occur at an interface (wind raindrops earthquakes)
Generating force = Restoring force
Surface waves on water–> 2 restoring forces?
Gravitational force
surface tension
Pressure in the vertical & buoyancy
Archimedes principle:
the upthrust force = the weight of water displaced
capillary waves
For waves with wavelengths less than about
1.7 cm, the principal restoring force is surface
tension
Gravity Waves
Travel On Density Surfaces
Wave Speed
(length of wave) / (wave period)
The period of a wave remains the same
(determined by generating force)
Wave trains
packets of similar waves with approximately the same
period and speed
Wave refraction
close to the shoreline. Waves
approaching shore at an angle first “feel bottom” close
to shore, slowing them down there and causing waves
to align themselves to the coastline
As a wave breaks, the energy it received from the wind is
dissipated.- where does it go
ØSome energy is reflected back out to sea.
ØMost of the energy is dissipated as heat and sound
(the ‘roar’ of the surf) in the final small-scale mixing of
foaming water, sand and shingle.
ØSome energy is used in fracturing large rock or
mineral particles into smaller ones.
ØSome energy is used to move sediments.
