Physical Oceanography Flashcards
What is the Coriolis Force
it is a change of direction.
- In Northern Hemisphere, wind is deflected to the right
- In the Southern Hemisphere, wind is deflected to the left
What is Frictional Coupling
when wind stress is transferred down into the water column due to internal friction
Why is the Coriolis force greater at higher latitudes
Due to a larger circumference at the equator, the equator spins faster than the poles do. This is why any water that drifts north of the equator is moving faster as it carries the speed from the equator with it. The Earth underneath is moving slower than the ocean and causes the water to spiral/spin/fan out.
What is a driver of oceanic motion
Solar radiation drives oceanic motion by heating and cooling the oceans.
What type of radiation is incoming radiation?
Shortwave radiation
What type of radiation is outgoing radiation
Longwave radiation
What is the radiation distribution on Earth?
(eg why poles get less concentrated radiation)
the closer to the equator you are, the more radiation you are exposed to.
at higher latitudes, the angle if the suns rays are deflected/scattered as the rays cover a larger surface area. Due to the curvature of the Earth, the rays are more concentrated at the equator and less concentrated towards the poles.
What are the 3 Milankovitch cycles
- Obliquity
- Orbital Precession
- Eccentricity
What is Obliquity? (Milankovitch Cycle)
Obliquity related to the tilt of the Earth
- moves in ~ 41,000 year cycles
- more tilt means more extreme seasons (eg closer/further away from the sun)
- less tilt means less extreme seasons (Earth is less crooked)
What is Orbital Precession? (Milankovitch Cycle)
Orbital precession is the wobble of the Earth
- moves in ~26,000 year cycles
- it makes seasonal contrasts more extreme in one hemisphere and less extreme in the other
- currently, the southern hemisphere experiences hotter summers while the northern hemisphere seasonal variations are more mild
What is Eccentricity? (Milankovitch Cycle)
the orbit around the sun changed to be more elliptical or more circular
- moves in ~ 100,000 year cycles
- more elliptical means more fluctuations
- more round means more equitable
Why is the northern hemisphere more sensitive to changes in climate?
The Northern hemisphere consists of a lot more landmass than the Souther hem. Land heats up faster than the oceans which is why is it more sensitive to changes in the climate and solar radiation.
How/why does the Earth distribute heat to the poles
Because there is an imbalance in the net surface heat flux, global circulation distributes heat from the equator to the poles through:
- wind
- deep ocean circulation
- surface currents
there is a surplus of heat energy at the equator and a net radiative loss at the poles.
think atmosphere and insolation
Why are there higher temperatures over landmasses than oceans?
This is due to:
Insolation
- land mass heats up more and faster in comparison to oceans
Atmosphere
- atmosphere over oceans has more water content so more clouds form over the water which disperse more of the incoming radiation
- water vapour absorbs about 20% of incoming radiation
State the mechanism of how ocean currents disperse heat
Surface waters at lower latitudes (equator) carry the heat polewards. The currents then get cooled in polar areas and get carried back to the equator
What is the albedo effect
It is the ability of a surface to reflect light.
darker surfaces absorb more heat energy, lighter surfaces reflect more heat energy
eg snow has a high albedo
What is the albedo feedback loop
Global warming causes more polar ice to melt. This means more light surfaces that reflect heat are being lost. this means the albedo keeps decreasing until a tipping point is reached and (in our lifetime) the Earth won’t be recovered
What is the layer in the water column called when there is a change in density
Pycnocline
How is density impacted by temperature and salinity?
Colder water is denser
Saltier water is denser
Why are colder waters more salty?
Warm surface waters move to the poles get colder and increase in salinity due to sea ice formation
cooler and saltier water is more dense so it sinks an pushes the bottom waters south
Where does rising of water occur?
the rising of water occurs in the Indian and Pacific Ocean because it warms up
this movement of warm water keeps Iceland and Greenland ice free in the summer
Facts about Broeckers Great Ocean Conveyor Belt
Wallace Broecker came up with it in 1980s
it was suggested that fluxes between heat and freshwater could cause a conveyor belt
What was the Young Dryas and what caused it?
type of circulation caused it…
an abrupt turn to glacial conditions and back to interglacial conditions
it was thought to be caused by a temporary shift in the thermohaline circulation
the temperature decrease and decreased by 10ºC in a decade
What is the Atlantic Meridional Overturning Current (AMOC)?
conveyor belt…
it carries warm water north in the Gulf Stream.
While water warms it evaporates and cools further north
- this increases the density and salinity of the seawater which drives the oceanic conveyor belt
Why might the AMOC slow down?
An increase in greenhouse gases warms the atmosphere which causes the surface of the ocean to retain more heat.
This leads to an increase in rainfall. A more active hydrological cycle increases the melting of ice, leading to an increase in freshwater inputs which impacts the density of water. The water will become less dense which leads to a weaker sinking mechanism which impacts the whole conveyor belt.
what happens if the AMOC weakens or collapses
The North will receive less warm water and Europe will get colder
What is Ekman Transport?
It is a wind driven current that shows that water transport from the wind travels at 90º to each other
this is due to friction and the Coriolis force
What are Gyres?
They are rotating current systems compromised of the Earths rotation (Coriolis effect) couples with currents and the prevailing winds
There is one big ‘whirlpool’ in the N. Hem. and one in the S. Hem which are called GEOSTROPHIC GYRES as they are a balance between the coriolis and the horizontal pressure gradient
What are the 6 main gyres?
- North Pacific Sub Tropical Gyre
- South Pacific Sub Tropical Gyre
- North Atlantic Sub Tropical Gyre
- South Atlantic Sub Tropical Gyre
- Indian Ocean Sub Tropical Gyre
- Antarctic circumpolar current (ACC)
What direction does the wind blow in the polar regions?
The winds blow west to east (50-70º N/S)
- this is the same direction in which the Earth spin
Why is circulation better in the south pole than it is in the north pole?
South pole circulation works well as it is a landmass surrounded by an ocean meaning nothing is obstructing the currents
North pole circulation doesn’t as the currents bump into the landmasses as it is an ocean surrounded by a landmass
What are the 4 types of currents?
- geostrophic currents
- western boundary currents
- eastern boundary currents
- transverse currents
Name the 5 Western Boundary Currents
- The Gulf Stream
- Brazil Current
- Agulhas current (Indian ocean)
- Kuroshio current (by Japan)
- East Australia current
What are the properties of WBCs
They are the
- fastest
- narrowest
- deepest
they form in the western side of an oceanic basin
they transfer warm water polewards due to the Coriolis force
Properties of the Gulf stream
- largest WBC
- moves with 2m/s
- 450m depth
- shifts the water 160km per day
- 70km wide and merges with the NA gyre and Sargasso Sea
- transports 55 sverdrups (sv)
- it meanders and loops and creates eddies
- because it is narrow it has distinct boundaries
What is a Sverdrup?
A unit of volume for the transport of 1 million cubic meters of water per second
- eg Gulf stream is 55sv
Why do eddies form?
They form due to the natural tendency of water to be turbulent and chaotic
this happens due to spatial variations in temperature, density and velocity
what is an eddie?
a circular current of water
How do eddies form?
small scale answer…. think what is happening
if one water mass is moving faster than another, horizontal and vertical shear forces can occur. This makes water turbulent and eddies can form.
They begin as small disturbances but will grow and develop into eddies which break off
Eddies need a rigid boundary for the shear force to occur
What direction do warm core eddies spin?
They spin clockwise and break off above the gulf stream
what direction do cold core eddies spin
They spin anti-clockwise and break off below the gulf stream
How big are eddies and how long can they last?
They can range from 10-500km in diameter and can last for more than 3 years.
They can also reach the seafloor
What are the properties of Eastern Boundary Currents?
- carry cold water to the equator
- form in the east of an ocean basin
- wider (~1000km)
- shallower (~2-4km deep)
- slower (eg Canary current only 16sv)
- they have no defined boundary due to width so no eddies form
What are the 5 EBCs?
- Canary current
- California current
- Peru/Humboldt current
- Benguela current
- Western Australia Boundary Current
What are Transverse currents?
they link Western and Eastern boundary currents to form big gyers
ie location and how they form
Properties of Transverse currents
- they move transversely
- they are derived from the stress of the wind with the spin of the earth
- found at the fringes of the tropics and at mid latitudes
- at the tropics, they go WEST
- at the mid latitudes they go EAST
What are the main transverse currents?
- North Pacific current
- North Equatorial Pacific Current
- South Equatorial Pacific Current
- North Equatorial Atlantic Current
- South Equatorial Atlantic Current
- North Atlantic Current
- ACC (also called West Drift)
Properties of the Transverse North and South equatorial current
The North and South equatorial currents are broad and shallow
they transport 30sv westward
Properties of the Transverse mid-latitude currents
they are broader and shallower than the equatorial currents due to the westerly winds (blowing east)