Physical oceanography
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.
Physical oceanography is one of several sub-domains into which
Physical oceanography may be subdivided into descriptive and dynamical physical oceanography.[1]
Descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precisely as possible.
Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and numerical models. These are part of the large field of Geophysical Fluid Dynamics (GFD) that is shared together with meteorology. GFD is a sub field of Fluid dynamics describing flows occurring on spatial and temporal scales that are greatly influenced by the Coriolis force.
Physical setting
External image | |
---|---|
Space and time scales of physical oceanographic processes.[2] |
Roughly 97% of the planet's water is in its oceans, and the oceans are the source of the vast majority of
From sea level, the oceans are far deeper than the
Body | Area (106km2) | Volume (106km3) | Mean depth (m) | Maximum (m) |
Pacific Ocean | 165.2 | 707.6 | 4282 | -11033 |
Atlantic Ocean | 82.4 | 323.6 | 3926 | -8605 |
Indian Ocean | 73.4 | 291.0 | 3963 | -8047 |
Southern Ocean | 20.3 | -7235 | ||
Arctic Ocean | 14.1 | 1038 | ||
Caribbean Sea | 2.8 | -7686 |
Temperature, salinity and density
This section needs expansion. You can help by adding to it. (June 2008) |
Because the vast majority of the world ocean's volume is deep water, the mean temperature of seawater is low; roughly 75% of the ocean's volume has a temperature from 0° – 5 °C (Pinet 1996). The same percentage falls in a salinity range between 34 and 35 ppt (3.4–3.5%) (Pinet 1996). There is still quite a bit of variation, however. Surface temperatures can range from below freezing near the poles to 35 °C in restricted tropical seas, while salinity can vary from 10 to 41 ppt (1.0–4.1%).[5]
The vertical structure of the temperature can be divided into three basic layers, a surface mixed layer, where gradients are low, a thermocline where gradients are high, and a poorly stratified abyss.
In terms of temperature, the ocean's layers are highly latitude-dependent; the thermocline is pronounced in the tropics, but nonexistent in polar waters (Marshak 2001). The halocline usually lies near the surface, where evaporation raises salinity in the tropics, or meltwater dilutes it in polar regions.[5] These variations of salinity and temperature with depth change the density of the seawater, creating the pycnocline.[3]
Circulation
Energy for the ocean circulation (and for the atmospheric circulation) comes from solar radiation and gravitational energy from the sun and moon.[6] The amount of sunlight absorbed at the surface varies strongly with latitude, being greater at the equator than at the poles, and this engenders fluid motion in both the atmosphere and ocean that acts to redistribute heat from the equator towards the poles, thereby reducing the temperature gradients that would exist in the absence of fluid motion. Perhaps three quarters of this heat is carried in the atmosphere; the rest is carried in the ocean.
The atmosphere is heated from below, which leads to convection, the largest expression of which is the
Oceanic currents are largely driven by the surface wind stress; hence the large-scale
Coriolis effect
The
Ekman transport
Ekman transport results in the net transport of surface water 90 degrees to the right of the wind in the Northern Hemisphere, and 90 degrees to the left of the wind in the Southern Hemisphere. As the wind blows across the surface of the ocean, it "grabs" onto a thin layer of the surface water. In turn, that thin sheet of water transfers motion energy to the thin layer of water under it, and so on. However, because of the Coriolis Effect, the direction of travel of the layers of water slowly move farther and farther to the right as they get deeper in the Northern Hemisphere, and to the left in the Southern Hemisphere. In most cases, the very bottom layer of water affected by the wind is at a depth of 100 m – 150 m and is traveling about 180 degrees, completely opposite of the direction that the wind is blowing. Overall, the net transport of water would be 90 degrees from the original direction of the wind.
Langmuir circulation
Langmuir circulation results in the occurrence of thin, visible stripes, called windrows on the surface of the ocean parallel to the direction that the wind is blowing. If the wind is blowing with more than 3 m s−1, it can create parallel windrows alternating upwelling and downwelling about 5–300 m apart. These windrows are created by adjacent ovular water cells (extending to about 6 m (20 ft) deep) alternating rotating clockwise and counterclockwise. In the convergence zones debris, foam and seaweed accumulates, while at the divergence zones plankton are caught and carried to the surface. If there are many plankton in the divergence zone fish are often attracted to feed on them.
Ocean–atmosphere interface
At the ocean-atmosphere interface, the ocean and atmosphere exchange fluxes of heat, moisture and momentum.
- Heat
The important
. In general, the tropical oceans will tend to show a net gain of heat, and the polar oceans a net loss, the result of a net transfer of energy polewards in the oceans.The oceans' large heat capacity moderates the climate of areas adjacent to the oceans, leading to a
- Momentum
Surface winds tend to be of order meters per second; ocean currents of order centimeters per second. Hence from the point of view of the atmosphere, the ocean can be considered effectively stationary; from the point of view of the ocean, the atmosphere imposes a significant wind
Through the wind stress, the wind generates
- Moisture
The ocean can gain
Planetary waves
- Kelvin Waves
A
Coastal Kelvin waves follow
Equatorial Kelvin waves propagate to the east in the
.Kelvin waves are known to have very high speeds, typically around 2–3 meters per second. They have wavelengths of thousands of kilometers and amplitudes in the tens of meters.
- Rossby Waves
There are two types of Rossby waves,
The special identifying feature of Rossby waves is that the phase velocity of each individual wave always has a westward component, but the group velocity can be in any direction. Usually the shorter Rossby waves have an eastward group velocity and the longer ones have a westward group velocity.
Climate variability
The interaction of ocean circulation, which serves as a type of
La Niña–El Niño
Antarctic circumpolar wave
This is a coupled
Ocean currents
Among the most important ocean currents are the:
- Antarctic Circumpolar Current
- Deep ocean (density-driven)
- Western boundary currents
- Gulf Stream
- Kuroshio Current
- Labrador Current
- Oyashio Current
- Agulhas Current
- Brazil Current
- East Australia Current
- Eastern Boundary currents
- California Current
- Canary Current
- Peru Current
- Benguela Current
Antarctic circumpolar
The ocean body surrounding the Antarctic is currently the only continuous body of water where there is a wide latitude band of open water. It interconnects the Atlantic, Pacific and Indian oceans, and provide an uninterrupted stretch for the prevailing westerly winds to significantly increase wave amplitudes. It is generally accepted that these prevailing winds are primarily responsible for the circumpolar current transport. This current is now thought to vary with time, possibly in an oscillatory manner.
Deep ocean
In the
Also see marine geology about that explores the geology of the ocean floor including plate tectonics that create deep ocean trenches.
Western boundary
An idealised subtropical ocean basin forced by winds circling around a high pressure (anticyclonic) systems such as the Azores-Bermuda high develops a
Equatorwards western boundary currents occur in tropical and polar locations, e.g. the East Greenland and Labrador currents, in the Atlantic and the Oyashio. They are forced by winds circulation around low pressure (cyclonic).
- Gulf stream
The Gulf Stream, together with its northern extension, North Atlantic Current, is a powerful, warm, and swift Atlantic Ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland to the northeast before crossing the Atlantic Ocean.
- Kuroshio
The Kuroshio Current is an ocean current found in the western Pacific Ocean off the east coast of Taiwan and flowing northeastward past Japan, where it merges with the easterly drift of the North Pacific Current. It is analogous to the Gulf Stream in the Atlantic Ocean, transporting warm, tropical water northward towards the polar region.
Heat flux
Heat storage
Ocean heat flux is a turbulent and complex system which utilizes atmospheric measurement techniques such as
Sea level change
Tide gauges and satellite altimetry suggest an increase in sea level of 1.5–3 mm/yr over the past 100 years.
The
Rapid variations
Tides
The rise and fall of the oceans due to tidal effects is a key influence upon the coastal areas. Ocean tides on the planet Earth are created by the gravitational effects of the Sun and Moon. The tides produced by these two bodies are roughly comparable in magnitude, but the orbital motion of the Moon results in tidal patterns that vary over the course of a month.
The ebb and flow of the tides produce a cyclical current along the coast, and the strength of this current can be quite dramatic along narrow estuaries. Incoming tides can also produce a tidal bore along a river or narrow bay as the water flow against the current results in a wave on the surface.
Tide and Current (Wyban 1992) clearly illustrates the impact of these natural cycles on the lifestyle and livelihood of Native Hawaiians tending coastal fishponds. Aia ke ola ka hana meaning . . . Life is in labor.
Tidal resonance occurs in the Bay of Fundy since the time it takes for a large wave to travel from the mouth of the bay to the opposite end, then reflect and travel back to the mouth of the bay coincides with the tidal rhythm producing the world's highest tides.
As the surface tide oscillates over topography, such as submerged seamounts or ridges, it generates
Tsunamis
A series of surface waves can be generated due to large-scale displacement of the ocean water. These can be caused by sub-marine landslides, seafloor deformations due to earthquakes, or the impact of a large meteorite.
The waves can travel with a velocity of up to several hundred km/hour across the ocean surface, but in mid-ocean they are barely detectable with wavelengths spanning hundreds of kilometers.
Tsunamis, originally called tidal waves, were renamed because they are not related to the tides. They are regarded as shallow-water waves, or waves in water with a depth less than 1/20 their wavelength. Tsunamis have very large periods, high speeds, and great wave heights.
The primary impact of these waves is along the coastal shoreline, as large amounts of ocean water are cyclically propelled inland and then drawn out to sea. This can result in significant modifications to the coastline regions where the waves strike with sufficient energy.
The tsunami that occurred in
Surface waves
The wind generates ocean surface waves, which have a large impact on
See also
- Climate change (general concept)
- CORA dataset temperature and salinity oceanographic dataset
- Downwelling
- Geophysical fluid dynamics
- Global Sea Level Observing System
- Global warming
- Hydrothermal circulation
- List of ocean circulation models
- List of Oceanic Landforms
- Marginal sea
- Mediterranean Sea
- Ocean
- Oceanography
- Thermohaline circulation
- Upwelling
- World Ocean Atlas
- World Ocean Circulation Experiment
References
- )
- ^ Physical Oceanography Archived 2012-07-17 at archive.today Oregon State University.
- ^ ISBN 0-7637-2136-0.
- ^ ISBN 0-13-018371-7.
- ^ ISBN 0-393-97423-5.
- ^ Munk, W. and Wunsch, C., 1998: Abyssal recipes II: energetics of tidal and wind mixing. Deep-Sea Research Part I, 45, pp. 1977--2010.
- ^ Talley, Lynne D. (Fall 2013). "Reading-Advection, transports, budgets". SIO 210: Introduction to Physical Oceanography. San Diego: Scripps Institute of Oceanography. University of California San Diego. Retrieved August 30, 2014.
- hdl:1912/5620.
- .
- ^ Goldman, Jana (March 20, 2012). "Amount of coldest Antarctic water near ocean floor decreasing for decades". NOAA. Archived from the original on 4 February 2022. Retrieved 30 August 2014.
- ^ "MyWorldCat list-OceanHeat". WorldCat. Retrieved Aug 30, 2014.
- ^ Stocker, Thomas F. (2013). Technical Summary In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press. p. 90.
- ^ "Tsuanmi Threats". Archived from the original on 2008-07-26. Retrieved 2008-06-28.
Further reading
- Gill, Adrian E. (1982). Atmosphere-Ocean Dynamics. San Diego: Academic Press. ISBN 0-12-283520-4.
- Samelson, R. M. (2011) The Theory of Large-Scale Ocean Circulation. Cambridge: Cambridge University Press. doi: 10.1017/CBO9780511736605.
- Maury, Matthew F. (1855). The Physical Geography of the Seas and Its Meteorology.
- Stewart, Robert H. (2007). Introduction to Physical Oceanography (PDF). College Station: Texas A&M University. OCLC 169907785. Archived from the original(PDF) on 2016-03-29.
- Wyban, Carol Araki (1992). Tide and Current: Fishponds of Hawaiʻi. Honolulu: University of Hawaiʻi Press. ISBN 0-8248-1396-0.
External links
- Way, John H. "Hypsographic curve". Archived from the original on 2007-03-30. Retrieved 2006-01-10.
- NASA Oceanography
- Ocean Motion and Surface Currents
- Ocean World (digital book)
- National Oceanographic and Atmospheric Administration
- University-National Oceanographic Laboratory System
- Pacific Disaster Center
- Pacific Tsunami Museum Hilo, Hawaii
- Science of Tsunami Hazards (journal)
- NEMO academic software for oceanography
- [1] History of Salinity Determination
[category; physicist of the lunar