patterns of water movement Flashcards
what are 3 types of currents depending on the factor that powers the flow?
Tidal currents - small scale (e.g. Race Rocks)
Wind-driven currents - major surface currents
(e.g. Gulf Stream, EAC)
Density-driven currents - major subsurface
currents (e.g. Great Ocean Conveyor)
what are the main gases that can be found in the atmosphere?
Nitrogen: 78.08% Oxygen: 20.94% Water vapor: 0-4% Argon: 0.93% Carbon dioxide: 0.035% Helium: 0.0005% Methane: 0.00015% Krypton: 0.00011% Hydrogen: 0.00005% Ozone: 0.000004%
what is the atmosphere structure?
Five layers characterized by differences in
temperature, composition, movement and density: from down to up
- troposhere (8-8-16)
- stratosphere 8-16-50
- mesosphrere (50 to 80km)
- ionosphere (80-600)
- exosphere (+ionosphere=thermosphere) (600-1000km)
troposphere
- Starts at earth’s surface
- Most dense layer - contains most of
atmosphere’s mass, water vapour and dust - Site and source of almost all weather
-varies with season, highest in summer, lowest in winter - Temperature decreases from 17oC to -75oC in troposphere as the distance from earth increases
- Contains most of water vapour and clouds in atmosphere
- Troposphere means “region of mixing”
- Wind speeds increase with height due to decreased friction
stratosphere
- Less dense than troposphere
- Dry → very low water vapour
- Lacks dust, ash, pollen
- Little vertical mixing - movement by diffusion only
- Temperature remains constant up to 25 km then it increases to -3oC due to UV absorption by ozone layer (at 20-30 km)
- 90% of ozone in atmosphere is the
stratosphere
explain the global wind pattern
- Air near the equator is warmed and rises because it is less dense than the air around
- The rising air creates a circulation cell, called a Hadley Cell, in which the air rises and cools at high altitudes moves outward (towards the poles) and, eventually, descends back to the surface.
- The continual heating and rise of air at the equator create low pressure there, which causes air to move (wind) towards the equator to take the place of the air that rises.
- sinking air creates high pressure at the surface where it descends. A gradient of pressure (high to low) is formed that causes air to flow away from the high and towards the low pressure at the surface.
- the Coriolis effect causes winds (and all moving objects) to be deflected:
- to the right in the Northern Hemisphere
- to the left in the Southern Hemisphere
The Coriolis effect causes winds to deflect as they travel within circulation cells and results in the two large hypothetical Hadley cells breaking into six smaller cells.
explain the unequal heating of Earth’s surface by
the sun
High solar radiation at the equator produces hot
air which rises because of its low density
In contrast, air at the poles is cold because of
low solar radiation - the cold air sinks because of
its high density which results in a high pressure
zone near the poles
Due to unequal heating of the Earth by the sun and the Coriolis force
An area at the equator receives more solar radiation than an equal area at the poles because of:
- The angle of exposure
- The distance the radiation travels through the atmosphere is less at the equator (the atmosphere absorbs part of the energy)
what’s coriolis force?
Objects that are moving relative to the ground are deflected to the right in the northern hemisphere and to the left in the southern hemisphere”
There is no Coriolis force at the equator AND
The amount of deflection increases with speed of the
moving object and with latitude
what’s atmospheric circulation?
the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth.
hadley cell
wind flow pattern of air rising at the
equator and descending at 30oN and 30oS
ferrel cell
at 30oN and 30oS some of the
descending air travels pole-ward - these surface
winds are deflected by the Coriolis force to
become the Westerlies of both hemispheres
polar cell
upper air moving pole-ward cools,
becomes dense and sinks back to the surface at the
poles
explain the global wind pattern
- Heating at equator causes air to warm, causing it to expand and results in a low pressure zone
- Warm air rises, expands and cools, losing moisture by precipitation and resulting in a high pressure zone
- Air flows toward low pressure zones, becoming cooler and drier which increases it’s density
- At 30 degrees N and S, the air sinks
- Much of this air returns to the equator along the surface, becoming warmer and picking up moisture along the way. The Coriolis force deflects the air, resulting in the Northeast Trade Winds and Southeast Trade Winds
- These trade winds converge at the equator resulting in light and variable winds (Doldrums) where wind is being convected upwards
- little wind at 30N/S (Horse Latitudes) because air is moving downwards
where do surface currents blow
Surface winds blow in regular patterns (due to unequal heating of the Earth and the Coriolis
force)
what causes the surface currents
by the drag of the wind on the water and the Coriolis force – water is set in motion by winds and affected by Coriolis force
explain Ekman transport
- The Coriolis force causes a deflection of the water
flow to the right (North) or left (South) - Each layer of water is deflected about 45o
- An Ekman spiral (A) is a rotating column of water that forms when water moves at an angle to the wind direction due to the Coriolis Effect.
- The net effect of the rotating water is movement at a right angle to the wind direction. The water turns to the left in the Southern Hemisphere.
what’s ekman transport?
Within each gyre, water piles up in the center and creates its own super intense Ekman spiral that intensifies the currents contributing to it
explain the surface currents
At low altitudes, trade winds produce westward moving currents
Westerly winds produce eastward moving currents at mid latitudes in both hemispheres
Currents are deflected by the continents creating gyres
how do surface currents vary? give examples
they vary in speed, depth and width:
Gulf stream and Kuroshio are the fasted (3-10 km/h), the deepest (1000-2000 m), and the narrowest (50-75 km)
Canary and California currents are slowest (~1 km/hr) and hundreds of kilometers wide
what is the Gulf stream, how does it work?
Western boundary current in the North Atlantic Gyre
Northward flow of warm water from the equator
The Gulf Stream, together with its northern extension the North Atlantic Drift, is a warm and swift Atlantic ocean current that originates in the Gulf of Mexico and stretches to the tip of Florida
what is the importance of the gulf stream?
Helps regulate temperature through this process
Moderates the climate as heat moves onto land
North Atlantic Current also helps push the warmer water out
Together they aid climate regulation in Western Europe and the Eastern USA
San Francisco and Dublin have similar climates despite San Francisco being 1600 km further south than Dublin
How to measure the wind-driven currents?
Current meter mounted on a mooring
ADCP: Acoustic Doppler Current Profiler: measure how fast water is moving across an entire water column.
Dyes, buoys, and drift cards
Davis drifter: A Davis drifter is an instrument designed to measure wind-driven surface currents. It has four major components: (1) body, (2) sails, (3) floats, and (4) a data collection/transmitter package.
what is upwelling?
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface
where does the upwelling occur?
Coastal upwelling occurs where Ekman transport moves water away from the coast
Surface waters are replaced by deep (cold and nutrient rich) water that comes up from below
Common on the west coasts of continents
what is downwelling?
the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. It is the sinking limb of a convection cell
where does downwelling occur?
In contrast, downwelling occurs where Ekman transport moves water toward the coast
Also occurs as water becomes more dense and sinks which occurs at the poles
what’s the el nino?
The periodic, irregular (every 2-7 years) disruption of trade winds due to the breakdown of the atmospheric pressure gradient
Without the wind, water is no longer pushed offshore from eastern Pacific and piled up in the western Pacific
Less upwelling, maybe some downwelling
Bad for plankton: No upwelling, no nutrients for plankton
Results in sea surface temperature anomalies
Very warm waters
what are the impacts of el nino?
Warmer water expands north and south of the equator
Range extensions of warm water species (mola mola), Humboldt squid, great white sharks
Atypical weather patterns
Increased precipitation in Ecuador and NW Peru
Droughts in agricultural regions of Bolivia and Southern Peru
Severe droughts in Australia, southern India, Indonesia, and Southern Africa
Severe coastal storms along west coast of North America, mild winter in Eastern North America
what is la nina?
Intensification of trade winds which results in more water being pushed toward the western Pacific
Colder water is pushed across from the eastern Pacific
Upwelling along west coast of South America is stronger
explain the deep ocean currents (thermohaline circulation)
describes the movement of ocean currents due to differences in temperature and salinity in different regions of water.
Density is a function of temperature and salinity
- Cold, salty water sinks which is what drives the thermohaline circulation
Dense water masses sink and displace less dense water masses
what is thermohaline circulation?
Dense water masses sink and displace less dense water masses
how does sea ice form?
during the thermohaline circulation, When saltwater rises, the salt gets left behind
what happens to the salt the is left behind during the thermohaline circulation?
Left behind salt gets cooled and then forms even more cold salty water
what is the great ocean conveyor?
The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity.
explain the great ocean conveyor belt
Driven by sinking in northern N. Atlantic
Warm salty surface water reaches the N. Atlantic (Gulf Stream) and cools and becomes more dense as salt is excluded during ice formation
This dense water sinks and flows south towards Antarctica (deep current)
There it is cooled further and continues to flow along the bottom of the ocean into Atlantic, Indian, and Pacific basins
Upwelling occurs in Pacific and Indian Oceans and water returns as surface flow to the North Atlantic
what’s the significance of the great ocean conveyor?
Helps oxygenate the deep sea and maintain nutrition levels
redistributes heat from equator to poles
Oxygenates deep oceans
Returns nutrients and CO2 from deep water to surface
how can you measure the great ocean conveyor?
Argo Floats (also used for measuring temp/salinity): Approximately every 10 days, an Argo float dives about 1.2 miles deep, drifts with the ocean currents, and then surfaces to transmit data in real-time via satellite
Moored buoys
how fast does the goc move?
Ranges between 12-20 sverdrups
1 sv = 1 million cubic meters/second
Gulf Stream ranges between 30sv in the Florida Current to a maximum of 150sv
GOC is NOT fast
