Circulation Flashcards
what causes surface tension and capillary action?
water cohesion
when is freshwater most dense?
4 C
Thermocline
is a layer of rapid temperature change between the mixed layer and deep water
Where is the ocean the most salty?
The water with the highest salt content is found where evaporation is greatest. This is in areas such as the Sargasso Sea in the North Atlantic where there is a pronounced high pressure system with lots of sunlight and little rain.
There is more rain at the equator so the ocean is less salty there
Temperature and salinity together have a major influence on seawater density… explain the relationship
As salinity increases, density increases.
As temperature increases, density decreases.
The —– is a zone of rapid salinity change.
halocline
The pycnocline is zone of rapid density change
pycnocline
thermohaline circulation
Temperature and salinity together affect seawater density. Differences in density from one place to another in the ocean drive ocean circulation. Nearer the poles, seawater cools and becomes more dense and it sinks.
how do gasses relate too seawater?
Gasses dissolve in seawater
Most important to life are oxygen, carbon dioxide and nitrogen gasses.
The colder the seawater, the more dissolved gasses it can hold
Because the earth is a sphere, which latitude receive less energy from the sun per area
higher (polar)
convection cell circulatory pattern
the reason we have atmospheric & water temperature differences between these two areas
transfer heat from one place to another by mass motion of a fluid such as water, air or molten rock. The heat transfer function of convection currents drives the earth’s ocean currents, atmospheric weather and geology.
Coriolis force
Because of the rotation of the earth, atmospheric and oceanic circulation becomes more complex.
Coriolis force deflects moving objects to the right in the northern hemisphere and to the left in the southern.
Convection cells
The earths atmospheric circulation cells are broken up into Hadley Cells between the Equator and temperate areas, and Ferrel Cells, between temperate and Boreal areas.
Rising air results in high rainfall. Descending air is dry. Thus rainforests are where air rises and deserts are where it descends.
Where are NE trade winds found under?
Hadley Cells
where are Horse latitudes (doldrums) found?
where the air descends.
where are prevailing westerlies found?
under ferrel cells
wind effects what?
the surface circulation
Ekman Spiral
Because the direction water is deflected turns more to the right as you go deeper in the water, overall, Ekman transport moves water 90 degrees to the wind.
When the Norwegian oceanographer Nansen was frozen into the Arctic ice for 3.5 years (in 1890s), he had a lot of time to watch the ice.
He noticed that when the wind blew over pieces of loose ice, they moved at about 45o to the right of the wind direction.
When he got home he asked a physicist friend, Ekman, about this, and Ekman explained what was happening (because of Coriolus force).
where are the eastern boundary currents?
Benguela…..Off SW Africa
Canary……… Off NW Africa
California….. Off California!
Humboldt …..Off NW South America
eastern boundary currents cause…
upwellings
Langmuir Circulation Cells
Wind blowing on water can set up small convection cells
On a windy day it is easy to see these cells. Buoyant material collects in lines where the water sinks.
monsoons in the Indian ocean
Winter Monsoon: land is cool, water is warm and wind blows from land to ocean.
Summer Monsoon: Land heats up and draws in moist oceanic air, thus causing heavy rains.
Intertropical Convergence Zone, or ITCZ
is the region that circles the Earth, near the equator, where the trade winds of the Northern and Southern Hemispheres come together. The intense sun and warm water of the equator heats the air in the ITCZ, raising its humidity and making it buoyant. Aided by the convergence of the trade winds, the buoyant air rises. As the air rises it expands and cools, releasing the accumulated moisture in an almost perpetual series of thunderstorms.
Equatorial Upwelling
Winds blowing along the equator deflect surface water (Coriolus Force again!) to the right in north and left in south
This leads to upwelling to replace the lost surface water
This nutrient rich water stimulates photosynthesis by phytoplankton
El Niño
Surface winds in tropical Pacific normally move from East to West.
Every 3-8 years High pressure builds up in W Pacific and Low pressure in E Pacific.
Winds then reverse direction (called Southern Oscillation)
This causes a reversal of water currents and warm water that had built up in W Pacific flows to the east and usually arrives around Xmas time and this stops the upwelling off Peru (called El Niño).
El Nino – Southern Oscillation abbreviated to ENSO
Major global effects from El Niño
Changes in weather patterns globally, more tornados in US
Warm water along California coast kills cold water species (i.e. Kelp), much higher rainfall.
Upwelling off Peru ceases, thus depressing anchovy fishery
Pacific Decadal Oscillation (PDO)
The PDO is detected as either warm or cold surface water north of 20N.
During a warm phase the Western Pacific becomes cool and the eastern Pacific becomes warm
The temperature of these waters shift ~20-30 years.
Warm or Positive PDO
Warm/humid air is advected along the US west coast and temperatures are higher than usual from the Pacific Northwest to Alaska but below normal in Mexico and the SE USA.
Winter precipitation is higher in Alaska Coast range, Mexico & SE USA
Using tree rings from California & Alberta the PDO has been reconstructed to year 993.
There are more frequent and intense El Niños During the warm PDO.
The PDO has been cool or negative since 1998. A strong El Niño could trigger the PDO to the warm phase.
This would lead to more rapid warming of the air in the SW USA.
The deep water circulation is about 90% of total water movement in the oceans and circulation is caused by
density differences from one place to another
Surface water circulation is the remaining 10% of oceanic water movement.
Global circulation of oceans
Major area of sinking of cold dense water which will become the ocean’s deep water is off Iceland & Greenland.
This water travels south and some upwells near Antarctica, then gets colder and more dense. Becomes Antarctic Bottom Water.
Rest of deep water travels to Pacific, slowly comes to surface, then slowly travels through the Indian Ocean, around S tip of Africa, then back to N Atlantic. Takes about 2000 yrs.
The Great Ocean Conveyer Belt
The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. The great ocean conveyor moves water around the globe. … As more warm water is transported north, the cooler water sinks and moves south to make room for the incoming warm water.
AMOC
In the Atlantic Ocean, this circulation system is termed the Atlantic Meridional Overturning Circulation or AMOC
A very cold period occurred called the “Younger Dryas”
The Younger Dryas was the most recent and longest of several interruptions to the gradual warming of the Earth’s climate since the severe LGM, about 27,000 to 24,000 years BP. The change was relatively sudden, taking place in decades, and it resulted in a decline of temperatures in Greenland by 4 to 10°C (7.2 to 18°F)[3]and advances of glaciers and drier conditions, over much of the temperate Northern Hemisphere. It is thought[4]to have been caused by a decline in the strength of theAtlantic Meridional Overturning Circulation, (AMOC) which transports warm water from theEquatortowards theNorth Pole, in turn thought to have been caused by an influx of fresh, cold water from melting of ice sheets in North America, to the Atlantic
Further weakening of the Atlantic Meridional Overturning Circulation (AMOC) could result in
more storms battering the UK,more intense wintersand an increase in damaging heatwaves and droughts across Europe.
Scientists predict that the AMOC will weaken further if global heating continues, and could reduce by about 34% to 45% by the end of this century,
spring tide
full and new moon stages when the sun, earth & moon are aligned. This is time of highest high and lowest low tides.
Neap Tides
(when high and low tides are minimum) occur when there is a half moon
What is a Nautical Mile?
A Nautical Mile has 6080 ft.
A KNOT is 1 Nautical Mile/hr. Remember that position on the earth is determined by latitude & longitude
A Nautical Mile is equal to one minute of latitude (not Longitude!)
Remember that each degree of latitude has 60 minutes
Deep water waves
occur where the orbits of water particles are near circular because the sea bottom (solid) is deeper that ½ wavelength.
Intermediate waves
occur where a wave can “feel” the bottom and the orbits of water particles are elliptical because the sea bottom (solid) is (½-1/20) wavelength.
Shallow water waves
occur where the depth is shallower than (1/20) wavelength.
Examples
1) wind waves in shallow water
2) tsunamis (seismic) waves
3) tide waves
Wave base depth
½ wavelength, where orbits do not move at all. If you get deep you won’t get battered as a scuba diver.
Capillary waves
(ripples) form when wind blows over the water
gravity wave
It forms when the wind strengthens and imparts more energy to the ocean. Unlike capillary waves, these waves have gravity as the major restorative (smoothing) force.
Tsunami
Caused by sudden movement of earth’s crust. Wave initially may be only 3-6 ft.
Incorrectly called a “tidal wave”
Have extremely long wavelengths (60-120 miles), and travel very fast (50-100 mph)
Are classified as a “shallow water wave”
When they come into shallower water, the wave height grows dramatically.
Wave height may be 20-100 ft high!
